Bacterial Transformation
Using Fluorescent Protein
Teacher Guide
sciencebridge
ScienceBridge/UC San Diego
© 2011
All rights reserved.
Content written/prepared by the following:
UCSD - ScienceBridge
Jeremy Babendure
Alegra Bartzat
Maarten Chrispeels
Heather Gastil
Shelley Glenn Lee
Heather Liwanag
Johnnie Lyman
James Short
Cover Image: Transformed E. coli fluorescing under UV light. Blue, green, and grape fluorescent proteins
are represented here (ScienceBridge PM1 mix).
TABLE OF CONTENTS Table of Contents
1
Program and Lab Overview
5
ScienceBridge Program. . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Lab Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2
Biology Curriculum
7
Lab Goals and Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
CA State Standards Addressed. . . . . . . . . . . . . . . . . . . . . . . . . 7
Content Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Research Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Checklist. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Glossary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
PowerPoint Notes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Teaching Strategies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Student Leader Preparation . . . . . . . . . . . . . . . . . . . . . . . 17
Protocols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Assessment Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Teacher Key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
P1
Protocol 1
21
P2
Protocol 2
27
A1 Appendix 1: Ecology of Fluorescent Proteins
35
1
PROGRAM AND LAB OVERVIEW |
Program and Lab Overview
ScienceBridge Program
About ScienceBridge
S
cienceBridge is a Science Outreach Initiative based at the University of California, San Diego (UCSD) that serves
secondary school teachers and students by connecting students to current and relevant scientific research through classroom
activities, university experiences and community events. The foundation of the ScienceBridge program is our Teacher Professional Development program, from which the following activity was developed at UCSD in collaboration with local science
teachers and is now offered as a training and implementation package for the high school classroom.
One primary goal of ScienceBridge is to create very affordable and accessible labs that engage students with authentic science
experiences. We work to optimize each activity to minimize the dependency on expensive equipment and other resources
sometimes lacking at a school site. In doing so, we have created activities that can be implemented in virtually ANY classroom, but are also able to be “ramped up” or have added complexity to challenge more advanced students or to utilize available classroom resources. ScienceBridge also supports and is helping to optimize student-run biotechnology sites within
specific school districts that will allow materials to be available and sustainable over time, eliminating dependency on external
resources.
Professional development & curricula
ScienceBridge’s Teacher Professional Development strives to create connections between teachers and scientists, increase
teachers’ and students’ access to current scientific information and resources, and encourage the engagement of students as
leaders in the classroom. Each ScienceBridge teacher is trained to use the materials and lab protocol created at UCSD and
brings a handful of students from his or her science classroom. These student leaders will learn to use the resources and serve
as teaching assistants and resident “experts” in the classroom during activity implementation. All student and teacher input is
encouraged and considered at all times, such that our training sessions, curriculum, and resources are the most effective and
useful to the audience.
We are very pleased to offer these resources to you and hope you have a great experience with this lab activity!
For more information and program updates, visit:
http://sciencebridge.ucsd.edu
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| BACTERIAL TRANSFORMATION USING FLUORESCENT PROTEIN
Lab Description
Bacterial transformation using fluorescent proteins
Bacteria have the unique ability to acquire and express new traits by incorporating foreign DNA from the environment into
their cells through their cell membranes. This process is called transformation and scientists utilize this process to create and
study DNA, genes, and gene products such as proteins. In this ScienceBridge lab activity, students will transform wild-type
E. coli bacteria with engineered DNA encoded with a gene for a fluorescent protein. In other words, normal bacteria will be
given the ability to create glowing proteins, resulting in glowing, fluorescent bacteria! The fluorescent proteins originate from
gene sequences that were optimized in the lab of Nobel Prize winner Dr. Roger Tsien at UCSD, and are widely used in scientific research to “tag” proteins of interest inside living cells in order to visualize cellular processes. What sets the ScienceBridge
activity apart from other transformation activities is the rainbow of colors. Instead of just one glowing color, students see an
array of colors that result from just slight mutations to the original fluorescent protein gene.
After completing this lab activity, students will have a better understanding of key biological and chemical processes such as
transcription and translation, the nature of cell membranes, and protein structure and function. Students will also gain important laboratory and technical skills while engaging in experimental design, data collection and analysis, communication of
findings, and sources of experimental error. Students and teachers alike will benefit from learning about and utilizing cuttingedge fluorescent protein technology in their very own classroom.
The ScienceBridge Bacterial Transformation activity can be used in many ways within the biology curriculum (Genetics:
Mutations, Ecology: Biodiversity, Evolution, Biotechnology) but may also benefit a Chemistry or Environmental Biology
classroom. Additionally, the activity can be expanded by utilizing the ScienceBridge Protein Purification protocol, in which
students learn how and why proteins are isolated, studied, and synthesized by scientists, and how these technologies are instrumental to scientific progress.
Green fluorescent protein. Note the barrel shape of the protein, with the chromophore in the center. The image at right
shows a cutaway so the chromophore can be seen more clearly.
2
BIOLOGY CURRICULUM |
Biology Curriculum
Lab Goals and Objectives
Irescent
n this lab, students will insert a gene that codes for a fluoprotein into bacteria, changing the genotype. After
the bacteria reproduce, transcribe, and translate the gene, students will observe the fluorescent color of the bacteria. This
change in phenotype (fluorescence) is due to the fluorescent
proteins inside the bacterial cells.
Lab Objectives
•
Genetics
Genes are a set of instructions encoded in the DNA sequence of each organism that specify the sequence of amino
acids in proteins characteristic of that organism.
•
Students know the general pathway by which ribosomes
synthesize proteins, using tRNAs to translate genetic
information in mRNA.
•
Students know how to apply the genetic coding rules to
predict the sequence of amino acids from a sequence of
codons in RNA.
•
Students know how mutations in the DNA sequence of
a gene may or may not affect the expression of the gene
or the sequence of amino acids in an encoded protein.
After completing this activity students will be able to:
1. Understand the concept of an experimental control.
2. Define, identify, and explain the process of bacterial
transformation.
3. Understand the central dogma of molecular biology
(DNA --> RNA --> protein --> trait).
4. Explain how a change in genotype leads to a change in
phenotype.
Students know the central dogma of molecular biology
outlines the flow of information from transcription of
ribonucleic acid (RNA) in the nucleus to translation of
proteins on ribosomes in the cytoplasm.
The genetic composition of cells can be altered by incorporation of exogenous DNA into the cells. As a basis for understanding this concept:
CA State Standards Addressed
•
The following CA state science standards are addressed in
the Bacterial Transformation Using Fluorescent Protein lab:
Students know the general structures and functions of
DNA, RNA, and protein.
•
Students know how genetic engineering (biotechnology)
is used to produce novel biomedical and agricultural
products.
•
Students know how basic DNA technology (restriction
digestion by endonucleases, gel electrophoresis, ligation,
and transformation) is used to construct recombinant
DNA molecules.
•
Students know how exogenous DNA can be inserted
into bacterial cells to alter their genetic makeup and support expression of new protein products.
Cell biology
The fundamental life processes of plants and animals depend
on a variety of chemical reactions that occur in specialized
areas of the organism’s cells.
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| BACTERIAL TRANSFORMATION USING FLUORESCENT PROTEIN
Investigation and Experimentation
Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding
this concept and addressing the content in the other four strands, students should develop their own questions and perform
investigations. Students will:
•
Select and use appropriate tools and technology (such as computer-linked probes, spreadsheets, and graphing calculators)
to perform tests, collect data, analyze relationships, and display data.
•
Identify and communicate sources for unavoidable experimental error.
•
Identify possible reasons for inconsistent results, such as sources of error or uncontrolled conditions.
•
Formulate explanations by using logic and evidence.
•
Recognize the issues of statistical variability and the need for controlled tests.
Content Information
Introduction
Transformation is a simple yet powerful technology used by scientists to alter the genetic code of a living organism. By understanding the central dogma of molecular biology and other biological and chemical processes, scientists have been able to take
genetic code from one organism and give it to another, resulting in major advances in health, medicine, and agriculture. In this
lab activity, students will alter the genetic makeup of bacterial cells by introducing a gene to produce a glowing protein.
Thymine
Adenine
5' end
O
O_
NH 2
P
_O
O
N
O
3' end
N
O
OH
HN
N
N
O
N
O
O_
O
O
O
_O
NH 2
P
O
N
P
O
N
HN
N
O
N
N
O
O H2N
PhosphateO
deoxyribose O P
_
backbone
O
O
O_
O
O
O
O
NH
H2N
N
N
O
O
O
O
_O
O
P
N
N
P
NH 2
O
O
N
NH
O
O_
O
H2N
N
O
O
O
N
N
O
P
N
N
O
O
O_
O
OH
3' end
Guanine
Cytosine
P
O
_O
5' end
The molecular structure of DNA, showing the specific pairing of the
nitrogenous bases (adenine:thymine, guanine:cytosine).
A comparison of the structure of RNA and DNA. DNA is comprised
of a double-stranded helix based on the sugar deoxyribose, and
utilizes the bases cytosine, guanine, adenine, and thymine. RNA is
comprised of single-stranded helix based on the sugar ribose, and
utilizes the bases cytosine, guanine, adenine, and uracil.
The central dogma of molecular biology
Proteins are the building blocks of living organisms, performing specific functions within the body such as providing structure
and support, carrying out enzymatic functions, regulating hormonal activities, and other vital processes. Proteins are coded by
an organism’s DNA, specifically sequences within the DNA called genes. Every protein is produced through a series of processes called transcription and translation, in which a gene within a strand of DNA is “read” and transcribed into a strand of
RNA, which is then “read” and translated into a protein using a collection of amino acids. This is known as the central dogma
of molecular biology (DNA --> RNA --> protein --> trait). The central dogma applies to all living cells, from the smallest
bacterium to the largest animal.
RESEARCH APPLICATIONS |
Bacteria
Bacteria are single-celled organisms classified as prokaryotes. They do not have nuclei, but they do have DNA. This DNA
is found on a single, circular chromosome that contains all of the genes the bacterium needs for its normal existence (its
genome). In addition, bacteria naturally contain one or more significantly smaller circular pieces of DNA called plasmids.
Plasmid DNA contains genes for traits that may be beneficial to bacterial survival under certain environmental conditions. In
nature, bacteria can transfer plasmids back and forth, allowing them to share these beneficial genes. This mechanism allows
bacteria to adapt to new environments. The recent occurrence of bacterial resistance to antibiotics is due to the natural transmission of plasmids.
DNA can be exchanged between bacterial cells in three ways.
1. Conjugation (bacterial “sex”) involves the exchange of DNA through direct cell-to-cell contact or through a bridge-like
connection between two cells called a sex pilus.
2. Transduction involves the transfer of DNA from one bacterial cell to another through a virus.
3. Transformation is the uptake of DNA from the environment surrounding the cell.
This unique ability of bacteria to move foreign plasmid DNA into their
cells is utilized by scientists to produce and study a variety of proteins,
including human proteins. Genes from one organism (e.g. human) can be
cut from the original DNA strand and inserted into plasmid DNA, which
may result in the bacteria producing the protein of interest (e.g. insulin).
Bacteria reproduce rapidly and are visible as colonies on a growth plate.
Each colony on the plate is the offspring of one original bacterial cell (a
clone of the original). A colony may represent millions of cells, all of which
are genetically identical, since they all came from the same original bacterium. The bacterium replicates not only its own circular chromosome, but
also its plasmid DNA. The bacteria utilized in this lab are Escherichia coli
(E. coli), which are rod-shaped bacteria that are often found in the human
digestive tract. E. coli are commonly used as model organisms in scientific
research.
E. coli colonies on agar
Genetic engineering
Scientists create plasmid DNA “vectors” to transfer genetic information between organisms. Scientists can determine the
unique sequence of a gene, copy or change it, and insert it into another organism’s DNA through genetic engineering. When
done in bacterial cells, this process is called transformation; when transformation is successful, a bacterium will be able to
make proteins it would normally be unable to, possibly giving it traits it did not previously have. When scientists apply this
technique to a multi-cellular organism, such as a plant or a mouse, and successfully alter its genetic makeup, it is called transgenic transformation.
To conduct a transformation, the gene to be transferred is placed into a plasmid DNA vector. This is done with the help of
restriction enzymes, which are naturally occurring enzymes from bacteria that recognize a particular sequence of DNA bases
and cut the DNA at that sequence. Bacteria use restriction enzymes to protect themselves from viruses that inject their DNA
into the bacteria; the enzymes can cut the viral DNA before it can hurt the bacteria. The same restriction enzyme is used to
cut the ends of the gene to be transferred and to cut open the circular plasmid DNA vector. Because the cuts are made using
the same restriction enzymes, the cuts have the same base sequence at the ends. These matching ends will match and reattach
when placed together with the aid of another enzyme, DNA ligase. Plasmid DNA vectors containing fluorescent protein (and
antibiotic resistance genes) have been constructed for use in this transformation lab.
Genetic transformation is used every day in many areas of biotechnology. In agriculture, genes coding for traits such as
drought resistance can be genetically transformed into plants. In bio-remediation, bacteria can be genetically transformed
with genes enabling them to digest hydrocarbons, to clean oil spills. Medical applications of transformation include the
creation of proteins, such as insulin (synthesized by Genentech) and factor VIII (blood clotting protein synthesized by Bayer).
9
10 | BACTERIAL TRANSFORMATION USING FLUORESCENT PROTEIN
Genes can be cut out of human, animal, or plant DNA and placed inside bacteria. Bacteria will then produce the “foreign”
protein coded by the gene in large quantities for therapeutic treatment. For example, a healthy human gene for the hormone
insulin can be put into bacteria and, under the right conditions, these bacteria can make authentic human insulin just as they
would make their own proteins. This insulin protein is then purified from the bacteria (see Protein Purification lab), and used
to treat patients with the genetic disease diabetes, in which the insulin gene does not function properly.
Transformed bacteria under plain light
Transformed bacteria under UV light
Bacterial Transformation
A bacterial cell has a cell wall and plasma membrane, which help the cell maintain an internal environment that is chemically distinct from the external environment. The cell wall and cell membrane serve as barriers that prevent the passage of
foreign material (including external DNA) into the cell. Because of these barriers, transformation can only occur under special
conditions. In the laboratory, scientists use a combination of techniques to help move the plasmid DNA vector through the
bacterial cell membrane.
In this lab, the bacteria are placed into a solution of calcium chloride (CaCl2). In solution, CaCl2 separates into calcium (Ca2+)
and chloride (Cl-) ions. It is thought that the calcium ions help to “shield” the negatively charged phosphates on the DNA,
helping the DNA pass through the phospholipids of the plasma membrane. The use of CaCl2 solution is combined with a
procedure known as heat shock. The heat shock procedure involves placing the bacterial solution on an ice bath, then heating the bacterial solution at a precise temperature for a very short period, and returning the bacterial solution to the ice bath.
This procedure is thought to “loosen” the phospholipids and create spaces between them to allow the DNA to pass through
the membrane. Placing the solution on ice slows the movement of the phospholipids and causes them to move close together.
The heat shock temporarily causes the phospholipids to move very quickly, and this sudden movement makes the membrane
more permeable to molecules like the DNA. Placing the bacterial solution on the ice bath
after the heat shock causes the phospholipids to slow down and helps “seal” the new DNA
FP gene
inside the cell. Note that the heat shock procedure must be carried out very precisely: if the
temperature is too hot or the time on heat is too long, the bacteria can die; if the temperature is too cold or the time on heat is too short, the DNA may not have the chance to move
across the membrane into the cell.
AmpR
Ampicillin
resistance gene
Schematic of the plasmid used in the ScienceBridge transformation lab. The plasmid
contains the gene for a fluorescent protein
and the gene for resistance to ampicillin.
To select only the bacteria that have successfully been transformed with the fluorescent
protein gene (in this lab), the plasmid DNA vector has also been engineered with a gene
for resistance to an antibiotic known as ampicillin (Amp). Ampicillin inhibits the growth
of the bacterial cell wall, which prevents the bacteria from growing. The ampicillin resistance gene codes for the production of the protein beta-lactamase, an enzyme that allows
the bacteria to digest the antibiotic before it can cause any harm. If ampicillin is mixed
into the agar (growth medium) on the bacterial plates, the only bacteria that can survive
on these plates will be bacteria with the gene/plasmid for ampicillin resistance. Therefore,
in the transformation procedure, if bacteria grow on the LB plates containing ampicillin,
they must have been successfully transformed. Any one of the different colored fluorescent
proteins can be inserted into the same place in this plasmid. In this lab, each DNA plasmid
IMPLEMENTATION | 11
vector has the gene that codes for one of six different fluorescent proteins. Plasmid mix 1 (PM1) has three different types of
plasmids: one with the gene for green fluorescent protein (GFP), one with the gene for blue fluorescent protein (BFP), and
one with the gene for Grape (a purple fluorescent protein). Plasmid mix 2 (PM2) is a mix of three more plasmids: one with
the gene for Cherry (a purplish-pink protein), one with the gene for Tangerine (a bright pink protein), and one with the gene
for yellow fluorescent protein (YFP). Your successfully transformed bacteria will fluoresce when exposed to a blacklight or UV
light (see previous page).
Fluorescence
Fluorescence occurs when light of one wavelength (or color) is absorbed and a light at a different wavelength (or color) is
re-emitted, usually at a slightly lower energy. Fluorescence can occur at any wavelength, but humans cannot observe much
of the electromagnetic spectrum visibly and need special instruments to detect fluorescence at other wavelengths outside the
visible spectrum. When utilizing fluorescence for research purposes, UV light is often the preferred wavelength for absorption
because the lower energy wavelength emitted is typically in the visible spectrum. The fluorescent proteins used in this lab can
glow because they contain a chromophore, a functional group which changes the shape of the molecule when excited by light.
Note that the grape fluorescent protein in the ScienceBridge lab does not fluoresce under UV light. A higher energy source
would be needed to cause fluorescence in the grape protein.
Research Applications
With the advent of genetic engineering in the late 20th century, many researchers have been able to place the gene that makes
their protein of interest into a plasmid. This allows them to make high quantities of the protein so that it can be studied
biochemically in isolation from other macromolecules in a cell. For example, if one wanted to study the characteristics of an
enzyme that causes an apple to turn brown after being cut, then he or she could isolate the gene for that enzyme, make a large
quantity of the protein, and then test how changes in temperature or pH affect it in a test tube. Once understood in isolation, that information could be used to devise a way to alter the enzyme’s function within the apple. (See the ScienceBridge
Enzyme/Substrate Reactions lab)
Isolating macromolecules and studying them separately from others has been a highly successful strategy to understand
biological processes; however, some questions cannot be answered in this way. Sometimes studying the macromolecule while
it is within the whole cell or organism would help a researcher answer a question best. But how do you see into a world that
is beyond your eyes’ ability to perceive? Fluorescent proteins have been utilized much like placing a flashlight at the end of
a protein. With the proper microscope, a protein that has been “tagged” with fluorescence can be observed within the cell,
moving around and interacting with other macromolecules. Several labs at UCSD utilize this technology to increase our understanding of cellular processes. The following labs utilize fluorescent proteins to see a new and wonderfully complex world
within living cells.
Klemke Lab
Dr. Richard Klemke, Pathology Department and Moores Cancer Center, UCSD
Utilizing a unique vertebrate model, the zebrafish, Dr. Klemke and his research
team study how cancer cells invade other tissue in a process called metastasis. A
cancer tumor needs a supply of nutrients and gas exchange to allow it to grow and
gain access to the blood system, so that individual cells may move from the original site and grow into a secondary tumor. The Klemke lab utilizes high resolution
microscopy to image zebrafish that have had their blood vessels tagged with GFP
(green fluorescent protein). Two types of human cancer cells are injected into the
fish. One type of human cancer is not metastatic and the other is metastatic; both
are identified by a different color – blue and red, respectively. Therefore, the metastatic cells that attract new blood vessel growth can be studied using microscopy
that allows for the creation of three-dimensional images of green blood vessels and
red tumor cells.
http://klemkelab.ucsd.edu
Transgenic zebrafish with blood vessels in
green with tumor cells in red.
12 | BACTERIAL TRANSFORMATION USING FLUORESCENT PROTEIN
Jin Lab
Dr. Yishi Jin, Division of Biological Sciences, UCSD
Understanding the development of nervous systems is the general area of study for
the Jin laboratory members. Their laboratory website lists four questions that frame
the studies conducted in the lab:
1. How are neurons that possess specific properties generated?
2. How are neurons guided to their targets?
GFP expression in C. elegans
3. How do neurons form synapses?
4. How do the synaptic connections remodel?
The answers to these questions are important because each neuron can form more than 1000 connections (synapses); however, these connections are dynamic. When we learn something new or form memories, we are actively improving or degrading connections between neurons. The model organism that the Jin lab uses is a transparent nematode approximately 1mm
in length that is naturally found in soil. Its transparency allows researchers to see within the organism in all stages of its life
(from fertilized egg to adult). By fluorescently tagging a protein involved in synapse development, scientists can study the
protein’s actions within the whole organism at any developmental stage. Understanding the molecular basis of the processes
involved could lead to significant advances in repairing spinal cord injuries.
http://biology.ucsd.edu/labs/yishijin/
Tsien Lab
Dr. Roger Tsien, Skaggs School of Pharmacy and Pharmaceutical Sciences
Sharing the Nobel Prize in Chemistry with Dr. Osamu Oshimomura and Dr. Martin
Chalfie, Dr. Roger Tsien helped develop the multiple fluorescent protein colors you see
in the following image from GFP (green fluorescent protein) and RFP (red fluorescent
protein). When the original GFP was made available to researchers to light up their favorite protein to study, many researchers wanted to visualize their protein within a living
cell or organism. With the development of the multiple colors, researchers could watch
many proteins interact in real time. Fluorescent microscopes and computer software
allowed for more detailed discoveries and even protein-to-protein interactions could be
identified when two different fluorescent proteins would combine to produce a distinct
color.
http://tsienlab.ucsd.edu/
Agar plate of fluorescent bacterial colonies
A variety of new and old localization methods are
used to visualize components of a cultured human
adenocarcinoma (HeLa) cell. The nucleus is labeled
with a small-molecule dye (blue), the Golgi apparatus
is immunolabeled with quantum dots (yellow), microtubules are genetically tagged with a fluorescent protein (green), and the actin cytoskeleton is labeled with
a tetracysteine/biarsenical pair (red). Image: National
Center for Microscopy and Imaging Research/B. N. G.
Giepmans. April 14, 2006
IMPLEMENTATION | 13
Classroom Implementation
Teacher preparation
One kit will have enough materials for a maximum of one class of 40 students, though it is recommended that you use one
kit per 32 students (eight groups of four students) so that you have extra materials. You can order enough kits for each of your
classes to implement the lab activity. You will have three things to prepare for the lab at least the day before you implement.
Bacterial Transformation Kit Checklist
Please contact your Tech Site immediately if you find that any items are missing or damaged:
Tech Site
Sara Dozier (scitechdozier@gmail.com)
UCSD Lab materials and Curriculum:
Heather Gastil (hgastil@ucsd.edu)
Store at room temperature
Store at 4°C (refrigerated)
___ (40) Transfer pipettes
Agar Plates
___ (10) Sterile transfer loops
___ (20) Small LB/amp agar plates (with red line)
___ (30) 2 mL clear round bottom microcentrifuge tubes
___ (20) Small LB only agar plates (no line)
___ (20) Cotton swabs
Plasmid Mix Bag
___ (10) CaCl2 blue 1.5 mL tubes with 1 mL each [50mM]
___ (1) PM1 green 0.6 mL tube: 15 μL @ 165ng/μL
___ (1) TE Buffer orange 1.5 mL tube with 1 mL total (10mM Tris, 1mM EDTA)
___ (1) PM2 purple 0.6 mL tube: 15 μL @ 165ng/μL
___ (10) Micropipette tips (for pre-streaking class plates)
Items not included in the kit
___ (1) Bacterial Stab (for making pre-streaks)
(Note: one stab/teacher - not one stab/kit)
___ (1) Cup with ice - crushed ice or ice/water mix
___ (1) Sharpie marker
___ (1) Waste container
___ (1) Hot water bath at 42°C
Prior to implementation
___ Print protocols
___ Aliqout DNA for lab groups
___ Make pre-streak bacteria plates (1-3 days before lab)
___ Prepare lab materials for each station
Day Before Implementation
(3 days if not using incubator)
(Do not leave “pre-streak” plates in incubator for more than 24 hrs)
___ Prepare bacteria starter plates or “pre-streaks”
___ Aliquot DNA plasmids for lab groups
14 | BACTERIAL TRANSFORMATION USING FLUORESCENT PROTEIN
Prepare bacteria “pre-streak” plates
Materials needed:
___ (10) LB only plates (no line)
___ Micropipette tips (found in bag of dry materials)
___ Bacterial stab (store at room temperature)
Note: The plates can be left at each lab station throughout the day.
1. Using a permanent marker, label the bacterial plate on the bottom of the plate, along
the edges, with “pre-streak” and the date.
2. Open the stab, and poke a sterile pipette tip down into the stab 3-4 times. Close the
stab.
3. Gently smear the bacteria on one edge of the LB agar plate (see diagram at right).
4. Discard the pipette tip in a biohazardous waste container*.
5. Using a new, sterile pipette tip, gently streak 4-5 lines from your original smear on the
LB agar plate.
6. Discard the pipette tip in a biohazardous waste container*.
7. Using a new, sterile pipette tip, gently streak 4-5 lines from the last set of lines, being careful to avoid the original smear.
8. Discard the pipette tip in a biohazardous waste container*.
9. Using a new, sterile pipette tip, gently streak 4-5 lines from last set of lines, being careful to avoid the original smear.
10. Discard the pipette tip in a biohazardous waste container*.
11. Incubate the pre-streak either at 37ºC overnight or 2-3 days if left at room temperature.
Note: Do not store plates in the refrigerator - only store plates at room temperature.
* Any materials that have touched bacteria are considered biohazardous waste. For safety compliance, you should collect these
materials in a rigid container and sterilize them by soaking them in a 10% bleach solution prior to discarding them. Once
sterilized, the materials may be discarded with the regular trash.
Aliquoting DNA Plasmids for lab groups
Materials Needed:
___ (1) PM1 tube (green)
___ (1) PM2 tube (purple)
___ (10) Clear 2 mL round bottom microcentrifuge tubes
___ (1) Orange 1.5 mL microtube TE buffer (1.0 mL of TE)
1. Add 0.5 mL of TE buffer to each PM1 and PM2 tube. This will almost fill up the PM1 and PM2 tubes. Gently
pipette up and down and then firmly close the tubes and invert them several times to ensure mixing. Make sure
to change pipette tips between mixes, so as not to transfer plasmids between tubes.
2. Using the provided clear 2 mL round bottom microcentrifuge tubes, label the caps: (5) tubes PM1 and (5) tubes
PM2.
3. Aliquot 0.1 mL into your labeled PM1 and PM2 tubes. You should have a total of (10) aliquots - 5 PM1 and 5
PM2. Again, make sure to change pipette tips between plasmid mixes to avoid transferring extra plasmids.
Note: The plasmid DNA in both PM1 and PM2 is concentrated (165 ng/μL), so there is only 15 μL present in the tube
before diluting. This is a small amount, so check the tubes for the 15μL before diluting. Often, some of the liquid gets caught
in the cap of the tube. It helps to spin the tubes briefly in a centrifuge, to bring the liquid down into the bottom of the tubes.
IMPLEMENTATION
| 15
Assembly of station materials
Have students label and assemble their group’s materials into a plastic bag. This acquaints them with the materials and helps
expedite set-up.
Note: There should also be at least one hot water bath or heating block set at 42°C (no higher). A hot water bath can be made
with a beaker of water and a hot plate.
Group materials
___ (1) Bacterial pre-streak (with bacterial colonies)
___ (2) LB/Amp plates (red line=ampicillin)
___ (1) LB only plate (no red line)
___ (2) 2.0 mL round bottom microcentrifuge tubes
___ (4) Disposable transfer pipets
___ (1) Sterile inoculation loop
___ (2) Cotton swabs
Place the following on ice
Items not included in kit
___ (1) Sharpie marker
___ (1) Cup with ice - crushed ice or ice/water mix
___ (1) Waste container
___ (1) Hot water bath at 42°C
FOR CLASS WASTE:
Prepare a 10% bleach solution in a tub or sink to soak all
waste materials. Soak materials (pipettes, plates, etc.) for
about 20 min in the solution and then they can be thrown in
a regular trash.
___ (1) 0.1 mL plasmid aliquot (PM1 or PM2)
___ (1) Blue 1.5 mL tube containing CaCl2
Glossary
Ampicillin (Amp)
An antibiotic (chemically similar to penicillin) that works
by inhibiting the synthesis (building) of bacterial cell walls.
Mixed with LB agar, it is used in this lab to select for transformed bacteria possessing the antibiotic resistance gene (the
gene for beta-lactamase) on the plasmid. Those that do not
have the plasmid with the antibiotic resistance gene (untransformed bacteria) will die in the presence of ampicillin.
Bacterial Stab
A small vial containing the ScienceBridge E. coli strain, untransformed, within LB agar. It is used for long-term storage
of bacteria and can be kept at room temperature (for several
weeks) or refrigerated (for a few months).
Bacterial Colony
A visible cluster of bacteria growing on an LB agar plate,
cultured from a single bacterium. Each colony should contain
only bacteria that are genetically identical. Even a small
colony can contain hundreds of thousands of bacteria.
Bacterium
The singular form of bacteria. A single E. coli bacterium is
rod-shaped, approximately two microns (μm) in length, and
half a micron wide.
CaCl2
Calcium chloride. During the transformation procedure, the
Ca2+ ions, formed when CaCl2 is put into the solution theoretically neutralize the negatively charged DNA, therefore
facilitating the movement of the DNA from outside of the
bacterial membrane to the inside of the cell. Also, the ions
can shield the negative charges on the phospholipids of the
cell membrane, once the movement of the phospholipids is
slowed by placing the sample on ice.
Central Dogma
The central dogma of molecular biology. This idea, first put
forth by Francis Crick in 1958, states that information in
living cells flows from DNA to RNA to protein, and never
in the reverse direction. This is the basis for a fundamental
understanding of molecular biology.
Escherichia coli
A gram-negative, rod-shaped bacterium that is commonly
found in the lower intestine of endothermic (warm-blooded)
animals. Commonly used as a model organism and more
commonly known as E. coli, this bacteria can also be found
outside the human body among fecally contaminated environments. Most strains of E. coli, including the one used in
this lab, are not harmful. The laboratory strain of E. coli has
had its entire genome sequenced.
16 | BACTERIAL TRANSFORMATION USING FLUORESCENT PROTEIN
Fluorescence
The absorption of electromagnetic radiation (light) by an
atom at a higher energy and the re-emission of electromagnetic radiation at a lower energy. See Appendix 1
Plasmid
A stretch of DNA that codes for a particular product (usually
a protein) that serves a function inside or outside the cell.
A small circular piece of DNA that replicates autonomously
within the bacterium. It is referred to as extrachromosomal
DNA because the bacterium has a single, circular chromosome that contains all of its regular genes. Plasmids replicate
themselves (separately from the bacterial chromosome), so
bacteria usually have multiple copies of the same plasmid in
a single cell.
Genome
PM1 (Plasmid Mix 1)
Gene
All of an organism’s hereditary information (its genes).
Genotype
The genetic makeup of an organism, usually in reference to a
particular characteristic. In other words, the genotype refers
to the specific “versions” of the genes in an organism’s DNA.
Heat Shock
The plasmid DNA mixture containing three different plasmids with three different fluorescent protein genes: grape,
blue, and green.
PM2 (Plasmid Mix 2)
Plasmid DNA mixture containing three different plasmids
with three different fluorescent protein genes: cherry, tangerine, and yellow.
A procedure used during bacterial transformation to facilitate the movement of DNA across the plasma membrane. In
this procedure, the bacterial cells are kept on ice, then placed
at 42°C for 45 seconds, and immediately put back on ice.
Theoretically, heat shock helps to open spaces between the
phospholipids of the plasma membrane, through which the
DNA can pass into the cell.
TE Buffer
LB Agar
The process by which RNA is synthesized (made) by copying
a sequence of an organism’s DNA (a gene).
LB stands for lysogeny broth, which contains nutrients that
support bacterial growth. While there is not one standard
mix for LB, it generally contains peptides and casein peptones, vitamins, trace elements such as nitrogen and sulfur,
and minerals. Agar is a gelatinous substance that most bacteria cannot digest.
Model Organism
A non-human organism used in scientific research to understand key aspects of biology, with the anticipation that the
results can help scientists understand the workings of other
organisms as well.
Phenotype
A characteristic that results from the expression of a gene. A
phenotype could manifest in the organism’s appearance (e.g.
color) or some other function (e.g. antibiotic sensitivity or
resistance).
A buffer containing Tris base [10 mM], a common pH buffer, and EDTA [1mM], a molecule that chelates cations, that
is used to dilute the plasmid DNA. It helps maintain the pH
and preserves the DNA.
Transcription
Transformation
A process in which bacteria take up foreign DNA from the
environment. Once that happens, the genes may be expressed. Introduction of foreign DNA into eukaryotic cells is
usually called transfection.
Translation
The process by which a protein is synthesized (made). During translation, messenger RNA (mRNA) is decoded by a
ribosome, which coordinates the binding of transfer RNA
(tRNA) to bring together amino acids in the correct sequence.
IMPLEMENTATION
| 17
PowerPoint Notes
The PowerPoint presentations that were given at both the teacher and student modules of the ScienceBridge training are
available on our website for your use in the classroom.
Embedded in the notes section of the student PowerPoint presentation are talking points for the presentation that can
printed out to use for your classroom lecture.
Download the files at http://sciencebridge.ucsd.edu. Once at the website, scroll over the top menu where it says
Programs=>ScienceBridge Labs=>Content Areas=>Transformation
On the page you will see a link titled PowerPoints. Click on the button and download the student PowerPoint.
Teaching Strategies
We suggest that you organize students in groups of four and have no more than eight lab groups. We give you enough materials for 10 groups, but using only eight groups is best to have extra materials on hand.
We have found that if you have the time, it helps to give the protocol to your students before the day of the implementation
so they can read through the steps. Assigning roles to the students ahead of time also helps the lab run smoothly on the day of
implementation.
It is also useful to print the Transformation Protocol Flow Chart (pg. 34 of this guide) for each lab station.
The curriculum is designed to be completed in three, 50-minute periods.
•
Day 1 – Prepare the students with the Student PowerPoint and pre-lab material. Organize lab groups and prepare
station materials.
•
Day 2 – Lab protocol
•
Day 3 – Results, analysis and conclusion
Student leader preparation
•
Meet with your student leaders before the implementation to answer any questions and review the
lab procedure with them.
•
Discuss how they can guide their fellow classmates
rather than just taking over the step or telling them
the answer.
•
If you are not having your classes prepare their
station materials, this a good task with which your
student leaders can assist you.
•
If you have student leaders assisting you in the
classroom for implementation, we suggest assigning
them to certain lab stations to guide the students at
each station through the protocol.
Protocols
There are two versions of the Bacterial Transformation Using
Fluorescent Protein protocol. All protocols contain pre- and
post-lab questions to guide student learning.
•
Protocol 1 – This protocol is text only with no
pictures.
•
Protocol 2 – This protocol is the same as the protocol that you used in the training, and has pictures to
assist your visual learners.
Assessment Strategies
This lab includes two stages of assessment in the protocol. Within the lab protocol, a pre-lab question set is designed to assess
student understanding of the Powerpoint material and prior knowledge of the lab subject area. A post-lab is provided for two
reasons: (1) to assess student understanding of results from the lab and (2) to allow for a comparison between all groups’ data
and promote sharing of data among groups. This will allow students to check their understanding of the results and to see all
six fluorescent protein colors.
18 | BACTERIAL TRANSFORMATION USING FLUORESCENT PROTEIN
Bacterial Transformation Using Fluorescent Protein
Teacher Key
Student pre-lab questions
1. What is a bacterial colony? How do the genotypes of individual bacteria in the same colony compare to each other?
A bacterial colony is a cluster of bacteria that originated from a single bacterial cell. All the bacteria in the same
colony should be genetically identical, so their genotypes should be exactly the same.
2. What is a gene? What processes occur to make a protein from a gene?
A gene is a section of DNA that codes for a product (often a protein) that serves some function for the cell. To
make a protein, the gene must first be transcribed into messenger RNA (mRNA) and the mRNA must be translated into the protein.
3. What is a plasmid?
A plasmid is a small, circular piece of DNA that is separate from the main chromosome in a bacterial cell.
4. What is transformation?
Transformation is a process in which bacteria take up foreign DNA from the environment.
5. What do the “+” and “-” on the microtubes indicate about the contents of each tube in the transformation procedure?
The “+” indicates that the plasmid has been added to the tube, and the “-” indicates that no plasmid has been
added.
6. What genes are present on the plasmid in this lab, and what is the function of each protein product?
The plasmid has a gene for a fluorescent protein, which makes the bacteria fluorescent (glows under UV light).
The plasmid also has a gene for ampicillin resistance, which allows the bacteria to grow in the presence of the
antibiotic ampicillin.
7. What does the red line on two of the plates indicate?
The red line means there is ampicillin in the plate.
8. What is the purpose of ampicillin (antibiotic) in the transformation procedure?
Ampicillin is used to select for the bacteria that have been transformed. Because the plasmid with the fluorescent
protein gene also has a gene for ampicillin resistance, only the transformed bacteria can survive in the presence of
ampicillin.
TEACHER KEY | 19
Plate #
Plasmid present?
Ampicillin present?
#1 LB/Amp (+)(red line)
YES
YES
NO
NO
#2 LB/Amp(-)(red line)
YES
YES
Expected Plate Results
(Drawing)
Students should draw a
plate with many individual colonies.
Expected Plate Results
(Description)
Transformed colonies (col- No growth
ored bacteria)
NO
NO
Students should draw a
plate with no growth.
#3 LB/No Amp(-)(no red line)
YES
YES
NO
NO
A plate with continuous
bacterial growth.
Bacterial “lawn”
Post-lab questions
1. Estimate the number of fluorescent colonies that grew on your experimental plates.
Transformation efficiency varies. If students have too many colonies to count, they can estimate the total number
of colonies by counting the colonies on one quadrant of the plate and multiplying by four.
2. Which plasmid mix did you have (PM1 or PM2) and which three colors of fluorescent colors of bacteria did you observe?
(Yes, three colors are present! Look again if you did not see them all!)
PM1: Green fluorescent protein (GFP), Blue fluorescent protein (BFP), Grape
PM2: Cherry, Tangerine, and Yellow fluorescent protein (YFP)
Note: The bacteria expressing BFP will look like “normal” colonies under white light but glow blue under UV
light. The Grape protein looks purple under white light and does not fluoresce under UV light (it requires a higher
energy light than UV to fluoresce).
3. What made it possible for the colonies to be different colors?
Each colony came from a single transformed bacterial cell that took in one of the plasmids with a fluorescent protein gene. There were three different kinds of plasmids in each mix (one for each color).
4. Describe how the plasmid was able to enter the cell. (Hint: There are two processes in the protocol that were designed to help the
plasmid get into the cell. What are they?)
Placing the bacteria in a solution of calcium chloride helped to neutralize the DNA, because the calcium (Ca2+)
ions “shielded” the negative charge on the DNA phosphates. Since charged molecules usually cannot pass through
the hydrophobic barrier of the plasma membrane, neutralizing the charge helps the plasmid move into the cell.
20 | BACTERIAL TRANSFORMATION USING FLUORESCENT PROTEIN
The heat shock procedure also helps the plasmid enter the cell. During the heat shock, the phospholipids in the
plasma membrane go from moving very slowly (when on ice) to moving very quickly (during the heat shock)
and then moving slowly again (when back on ice). When the phospholipids suddenly move very quickly, spaces
are created in the plasma membrane through which the plasmid can pass.
5. There are two controls in this experiment: the LB/Amp (-) plate and the LB/No Amp (-) plate. What are they testing?
Assuming the lab procedure was performed correctly, what would it mean if bacteria grew on the LB/Amp (-) plate? What
would it mean if no bacteria grew on the LB/No Amp (-) plate?
The LB/Amp (-) plate tests whether the ampicillin is working properly. The LB/Amp (-) plate contains ampicillin and the bacteria were not given the plasmid. If bacteria grow on the LB/Amp (-) plate, it could mean that
the ampicillin was not working because the ampicillin should kill any bacteria that do not have the plasmid.
The LB/No Amp (-) plate tests whether the bacteria are viable. The LB/No Amp (-) plate does not contain ampicillin and the bacteria were not given the plasmid. If no bacteria grow on the LB/No Amp (-) plate, it could
mean that the bacterial cells were unable to grow. (If the heat shock procedure is too hot or too long, the bacterial
cells can die.)
6. How can transformation be used in the medical industry or in research?
Because transformation allows bacteria to express a gene that has been engineered, it is widely used in medicine
and research to produce proteins in bacterial cells. Many proteins (e.g. insulin, epinephrine) can be produced in
bacterial cells. Scientists can also insert a gene into a cell to see what it does - they change the genotype to observe
the effects on the phenotype and learn the purpose of the gene. Fluorescent proteins are produced by bacteria and
used in research to “tag” other proteins or molecules and to visualize cellular processes.
PROTOCOL 1
| 21
Bacterial Transformation Using Fluorescent Protein Central question
How does a change in the genotype of an organism affect its phenotype?
Overview of experiment
In this lab, you will insert a gene that codes for a fluorescent protein into bacteria, changing the genotype. After the bacteria
reproduce, transcribe, and translate the gene, you will observe a change in the phenotype (appearance) of the bacteria.
How will the addition of a gene for a fluorescent protein affect the phenotype of the
bacteria? − Hypothesis
Student pre-lab questions
1. What is a bacterial colony? How do the genotypes of individual bacteria in the same colony compare to each other?
2. What is a gene? What processes occur to make a protein from a gene?
3. What is a plasmid?
4. What is transformation?
5. What do the “+” and “-” on the microtubes indicate about the contents of each tube in the transformation procedure?
22 | BACTERIAL TRANSFORMATION USING FLUORESCENT PROTEIN
6. What genes are present on the plasmid in this lab, and what is the function of each protein product?
7. What does the red line on two of the plates indicate?
8. What is the purpose of ampicillin (antibiotic) in the transformation procedure?
Based on your answers to the questions above, predict the results of your transformation procedure in the table below.
Plate #
Plasmid present?
Ampicillin present?
Expected Plate Results
(Drawing)
Expected Plate Results
(Description)
#1 LB/Amp (+)(red line)
YES
YES
NO
NO
#2 LB/Amp(-)(red line)
YES
YES
NO
NO
#3 LB/No Amp(-)(no red line)
YES
YES
NO
NO
PROTOCOL 1 | 23
Lab Procedure
Group #
Assign group roles:
Materials: Gathers and organizes group materials, and assists with disposal.
Reader: Reads the protocol aloud so group members can follow the steps.
Timer: Keeps track of timing for all timed steps. This is especially important for the heat shock!
Technician: Carries out the actual steps of the protocol.
Role in Group
Student Name
Materials
Reader
Timer
Technician
Materials checklist
___ (1) ScienceBridge Transformation Protocol
___ (1) Bacterial pre-streak plate with bacterial colonies
___ (1) Agar plate containing LB/No Amp (no red line)
___ (2) Agar plates containing LB/Amp (red line)
___ (1) Sterile inoculating loop
___ (4) Plastic transfer pipettes
___ (2) Clear 2.0 mL microtubes
___ (2) Cotton Swabs
___ (1) Piece of tape for sealing plates after inoculation
___ (1) Waste container
___ (1) Styrofoam cup with ice
ON ICE
___ (1) Blue 1.5 mL tube of CaCl2
___ (1) Clear 2.0 mL tube of plasmid DNA labeled either “PM1” or “PM2”
Shared materials for class
___ Hot water bath at 42ºC
___ (1) Sharpie
NOTE: When labeling plates, write on the BOTTOM of
the plate (not the lid) and keep writing small and close to the
edges!
1. Label plates all three plates with the date, class period
and your group number or initials as listed below:
Plate #
Label
1
“LB/Amp (+)” (positive)
2
“LB/Amp (–)” (negative)
3
“LB/No Amp (–)” (negative)
(+)
LB/Amp
(-)
LB/Amp
Name/Period
Name/Period
#2
#1
Amp (-)
LB/No
#3
Name/Perio
d
24 | BACTERIAL TRANSFORMATION USING FLUORESCENT PROTEIN
2. Close the caps on two microtubes and label each cap: one tube with a “+”, other tube with a “–”
3. Using a plastic transfer pipette transfer 0.5 mL of CaCl2 to each tube, close and place both tubes on ice for at least 2
minutes. Discard the pipette in the waste container.
4. Using a sterile loop, gently collect ONE colony (“dot”) of bacteria from the top of your bacterial starter plate, being careful not to gouge the agar. Transfer the collected colony to one tube of CaCl2. Swirl and twist the loop to make sure all the
bacteria mix with the CaCl2 solution. Mix the contents by inverting the tube or flicking. The solution should look cloudy
with no chunks.
5. Transfer ONE additional colony to the second tube by repeating instruction #4. Place the tubes back on ice.
6. Using a clean plastic pipette, add all of the plasmid mix solution (labeled either “PM1” or “PM2”) into the positive (+)
tube with CaCl2. BE SURE THAT THE PLASMID IS ONLY TRANSFERRED TO THE + TUBE. Mix. Discard
the used pipette.
7. Incubate both tubes on ice for 10 minutes. Make sure the tubes are immersed in the ice.
8. The timer and one other group member will:
•
Check the water bath temperature to ensure it is at 42ºC.
•
Hold the tubes in the hot water for exactly 45 seconds. Make sure that the tubes are in contact with the hot water.
•
Immediately return the tubes to the ice for 2 minutes.
9. Invert your tubes gently to mix. Using a new pipette, transfer 0.25 mL of the cell mixture from the (-) negative tube to
the LB/Amp (-) agar plate. Spread the mixture around the plate gently with a clean cotton swab.
10. With the same pipette, transfer 0.25 mL of the cell mixture from the (-) negative tube to the LB/No Amp (-) agar plate.
Spread the mixture around the plate gently with the same cotton swab. Make sure to completely finish the two “-“ (negative) plates before spreading the cells on the “+” (positive) plate.
11. With a new clean pipette, transfer 0.25 mL of the cell mixture from the (+) positive tube to the LB/Amp (+) plate.
Spread the mixture around the plate gently with a clean cotton swab.
12. Stack your plates, tape them together, put plates UPSIDE DOWN to grow overnight in 37ºC incubator.
PROTOCOL 1
| 25
Post lab questions
Now that you have performed a transformation, fill out the table below to describe your results.
Plate #
Plasmid present?
Ampicillin present?
Actual Plate Results
(Drawing)
#1 LB/Amp (+)(red line)
YES
YES
NO
#2 LB/Amp(-)(red line)
NO
YES
YES
NO
NO
#3 LB/No Amp(-)(no red line)
YES
YES
NO
NO
Actual Plate Results
(Description)
1. Estimate the number of fluorescent colonies that grew on your experimental plates.
2. Which plasmid mix did you have (PM1 or PM2) and which three colors of fluorescent colors of bacteria did you observe?
(Yes, three colors are present! Look again if you did not see them all!)
3. What made it possible for the colonies to be different colors?
26 | BACTERIAL TRANSFORMATION USING FLUORESCENT PROTEIN
4. Describe how the plasmid was able to enter the cell. (Hint: There are two processes in the protocol that were designed to help the
plasmid get into the cell. What are they?)
5. There are two controls in this experiment: the LB/Amp (-) plate and the LB/No Amp (-) plate. What are they testing?
Assuming the lab procedure was performed correctly, what would it mean if bacteria grew on the LB/Amp (-) plate? What
would it mean if no bacteria grew on the LB/No Amp (-) plate?
6. How can transformation be used in the medical industry or in research?
Conclusion / summary (revisit hypothesis)
PROTOCOL 2 | 27
Bacterial Transformation using Fluorescent Protein Central question
How does a change in the genotype of an organism affect its phenotype?
Overview of experiment
In this lab, you will insert a gene that codes for a fluorescent protein into bacteria, changing the genotype. After the bacteria
reproduce, transcribe, and translate the gene, you will observe a change in the phenotype (appearance) of the bacteria.
How will the addition of a gene for a fluorescent protein affect the phenotype of the
bacteria? − Hypothesis
Student pre-lab questions
1. What is a bacterial colony? How do the genotypes of individual bacteria in the same colony compare to each other?
2. What is a gene? What processes occur to make a protein from a gene?
3. What is a plasmid?
4. What is transformation?
5. What do the “+” and “-” on the microtubes indicate about the contents of each tube in the transformation procedure?
28 | BACTERIAL TRANSFORMATION USING FLUORESCENT PROTEIN
6. What genes are present on the plasmid in this lab, and what is the function of each protein product?
7. What does the red line on two of the plates indicate?
8. What is the purpose of ampicillin (antibiotic) in the transformation procedure?
Based on your answers to the questions above, predict the results of your transformation procedure in the table below.
Plate #
Plasmid present?
Ampicillin present?
Expected Plate Results
(Drawing)
Expected Plate Results
(Description)
#1 LB/Amp (+)(red line)
YES
YES
NO
NO
#2 LB/Amp(-)(red line)
YES
YES
NO
NO
#3 LB/No Amp(-)(no red line)
YES
YES
NO
NO
PROTOCOL 2 | 29
Bacterial Transformation Group #
Assign group roles:
Materials: Gathers and organizes group materials, and assists with disposal.
Reader: Reads the protocol aloud so group members can follow the steps.
Timer: Keeps track of timing for all timed steps. This is especially important for the heat shock!
Technician: Carries out the actual steps of the protocol.
Role in Group
Student Name
Materials
Reader
Timer
Technician
Materials checklist
___ (1) ScienceBridge Transformation Protocol
___ (1) Piece of tape for sealing plates after inoculation
___ (1) Bacterial pre-streak plate with bacterial colonies
___ (1) Waste container
___ (1) Agar plate containing LB/No Amp (no red line)
___ (1) Styrofoam cup with ice
___ (2) Agar plates containing LB/Amp (red line)
ON ICE
___ (1) Sterile inoculating loop
___ (1) Blue 1.5 mL tube of CaCl2
___ (4) Plastic transfer pipettes
___ (1) Clear 2.0 mL tube of plasmid DNA labeled either “PM1” or “PM2”
___ (2) Clear 2.0 mL microtubes
___ (2) Cotton swabs
Shared materials for class
___ Hot water bath at 42ºC
___ (1) Sharpie
Lab procedure
NOTE: When labeling plates, write on the BOTTOM of
the plate (not the lid) and keep writing small and close to the
edges!
1. Label plates all three plates with the plate number, date,
class period and your group number or initials as listed
below:
Plate #
Label
1
LB/Amp (+) (red line)
2
LB/Amp (–) (red line)
3
LB/No Amp (–) (no red line)
+)
LB/Amp (
(-)
LB/Amp
Name/Period
Name/Period
#2
#1
Amp (-)
LB/No
#3
Name/Perio
d
30 | BACTERIAL TRANSFORMATION USING FLUORESCENT PROTEIN
2. Close the caps on two microtubes and label each cap
with a sharpie: one tube with a “+”, other tube with a “–”
3. Using a plastic transfer pipette transfer 0.5 ml of
CaCl2 to both tubes, close and place them on ice for
at least 2 minutes. Discard the pipette in the waste
container.
+
0.5 mL
CaCl2
+
-
-
4. Using a sterile loop, gently collect ONE colony (“dot”)
of bacteria from the top of your bacterial pre-streak
plate. Transfer the collected colony to one tube of CaCl2.
Swirl and twist the loop to make sure all the bacteria mix with the CaCl2 solution. Mix the contents by
inverting the tube or flicking the bottom of the tube. The
solution should look cloudy with no chunks.
5. Transfer ONE additional colony to the second tube and
repeat instruction #4. Place the tubes back on ice.
6. Using a clean plastic pipette, add all of the plasmid
mix solution (labeled either “PM1” or “PM2”) into the
positive (+) tube with CaCl2 BE SURE THAT THE
PLASMID IS ONLY TRANSFERRED TO THE +
TUBE. Mix. Discard the used pipette.
DNA
+
(plasmid)
7. Incubate both tubes on ice for 10 minutes. Make sure
the tubes are immersed in the ice.
10 minutes
PROTOCOL 2 | 31
8. The timer and one other group member will
•
•
•
Check the water bath temperature to ensure
it is at 42ºC.
42o
Hold the tubes in the hot water for exactly
45 seconds. Make sure that the tubes are in contact with the hot water.
Immediately return the tubes to the ice for
2 minutes.
2 minutes
45 seconds
Plate #3
9. Invert your tubes gently to mix. Using a new pipette,
transfer 0.25 mL of the cell mixture from the (-) negative tube to the LB/No Amp (-) agar plate. Spread the
mixture around the plate gently with a clean cotton
swab.
LB/No Amp (-)
0.25 mL
-
Plate #2
10. With the same pipette, transfer 0.25 mL of the cell mixture from the (-) negative tube to the LB/Amp (-) agar
plate. Spread the mixture around the plate gently with
the same cotton swab. Make sure to completely finish
the two “-” (negative) plates before spreading the cells on
the “+” (positive) plate.
LB/Amp (-)
0.25 mL
-
Plate #1
LB/Amp (+)
11. With a new clean pipette, transfer 0.25 mL of the cell
mixture from the (+) positive tube to the LB/Amp (+)
plate. Spread the mixture around the plate gently with a
clean cotton swab.
+
0.25 mL
37o
12. Stack your plates, tape them together, put plates
UPSIDE DOWN to grow overnight in 37ºC incubator.
Amp (-)
LB/No
#3
Name/Perio
d
32 | BACTERIAL TRANSFORMATION USING FLUORESCENT PROTEIN
Post-Lab Questions
Now that you have performed a transformation, fill out the table below to describe your results.
Plate #
Plasmid present?
Ampicillin present?
Actual Plate Results
(Drawing)
#1 LB/Amp (+)(red line)
YES
YES
NO
#2 LB/Amp(-)(red line)
NO
YES
YES
NO
NO
#3 LB/No Amp(-)(no red line)
YES
YES
NO
NO
Actual Plate Results
(Description)
1. Estimate the number of fluorescent colonies that grew on your experimental plates.
2. Which plasmid mix did you have (PM1 or PM2) and which three colors of fluorescent colors of bacteria did you observe?
(Yes, three colors are present! Look again if you did not see them all!)
3. What made it possible for the colonies to be different colors?
PROTOCOL 2 | 33
4. Describe how the plasmid was able to enter the cell. (Hint: There are two processes in the protocol that were designed to help the
plasmid get into the cell. What are they?)
5. There are two controls in this experiment: the LB/Amp (-) plate and the LB/No Amp (-) plate. What are they testing?
Assuming the lab procedure was performed correctly, what would it mean if bacteria grew on the LB/Amp (-) plate? What
would it mean if no bacteria grew on the LB/No Amp (-) plate?
6. How can transformation be used in the medical industry or in research?
Conclusion / summary (revisit hypothesis)
34 | BACTERIAL TRANSFORMATION USING FLUORESCENT PROTEIN
Transformation Protocol Flow Chart
Positive tube (+)
Negative Tube (-)
500 μL CaCl2
ON ICE!
500 μL CaCl2
ON ICE!
One (1) Bacteria Colony
Vortex or Shake to Mix
One (1) Bacteria Colony
Vortex or Shake to Mix
+
-
FP gene
100 μL Plasmid (PM1 or PM2)
Tap Tube Gently
No Plasmid
AmpR
Ampicillin
resistance gene
ICE
HEAT
ICE
45 Second Heat Shock
ICE
HEAT
ICE
45 Second Heat Shock
100 μL on LB/Amp (+) Plate
100 μL on LB/Amp (-)
and
LB Only (-) Plates
LB/Amp (+)
LB/Amp (-)
LB Only (-)
APPENDIX 1
| 35
Appendix 1 - Ecology of Fluorescent Proteins
The discovery of fluorescent proteins has been revolutionary
in its applications for medical and biological research (biotechnology). But where did the original proteins come from?
Why do they exist? How do they work in nature? And what
organisms use fluorescence and why?
The many-colored fluorescent proteins used in the transformation activity all originated from one of two proteins found
in nature: the green fluorescent protein (GFP)— discovered
in and isolated from a marine jellyfish (Aequorea victoria)
and red fluorescent protein (dsRed), a protein more recently
discovered in a particular group of corals (“mushroom” corals,
Discosoma spp.). These fluorescent proteins are light harnessing and light emitting molecules whose function in nature
remains a mystery. Meanwhile, fluorescent proteins have
been and continue to be extensively studied and engineered
in the research lab as powerful molecular markers.
While studying the bioluminescence of the crystal jelly,
Shimomura found it odd that the light created by the jelly
was blue, yet the color being expressed by the jelly was green!
How and why does this jelly convert its blue light to green?
The answer to “how” is that the jelly was producing a protein
that absorbed the blue light and emitted green light. Shimomura discovered this protein and named it “GFP” (green
fluorescent protein). He described its structure and function which provided the foundation for decades of scientific
progress in molecular research. However, no scientist has yet
figured out why the jelly prefers green light to blue, or how
the jelly uses its light in the ocean.
Fluorescence vs. bioluminescence
In the deep sea, more than 90% of organisms are capable of
producing their own light through bioluminescence. From
bacteria to squid to fish, bioluminescence is an adaptation
for survival and is used for either finding food by locating or
attracting prey (e.g. lure of anglerfish, below), for protection
against predators (e.g. counter-illumination in the hatchetfish), or for communication between individuals of a given
species (e.g. light patterns in firefly squid.)
Aequorea victoria
Discovery of GFP
In the 1960’s, a marine biologist named Osamu Shimomura
was interested in the bioluminescent behavior of the crystal
jellyfish Aequorea victoria. Bioluminescence is the ability of
a living organism to create its own light through a chemical
reaction. In the sea, this adaptation (a behavior or structure
that is passed from one generation to another and allows
an organism to better survive within a particular environment) is prominent in the sea, especially the deep sea, where
fish, shrimp, and other organisms use light to attract mates,
find food, or protect themselves from harm. The crystal jelly
studied by Shimomura is not a deep sea organism, but is
abundant in the waters of the Pacific Northwest.
Female angler fish
In most cases of bioluminescence, the light is created through
a chemical reaction between a substrate (“luciferin”) and an
enzyme (“luciferase”) in the presence of oxygen. The light
is produced in an organ called the photophore and one or
more photophores are strategically located on the body of an
organism depending on how the light is used.
36 | BACTERIAL TRANSFORMATION USING FLUORESCENT PROTEIN
Although organisms are seemingly capable of producing different colors of light, blue is the most common color used by
marine organisms. Blue light (short wavelength light) tends
to scatter in water and penetrate farther than colors such as
red and orange (long wavelength light), which tend to be absorbed by water rather quickly. If you take a red object under
water with you, the deeper you go the less red it will appear.
This happens because there is a decreasing amount of red
light available to reflect back to your eye. (Remember that a
red apple appears red because it absorbs all other colors and
reflects red light. If there is no red light available, the apple
will look gray or black). To take advantage of this phenomenon, many deep sea organisms are red in color, as there is
no red light available to reflect off of them, thus they “blend”
into the darkness rather well. In the sea, the blue light created by bioluminescence is definitely meant to be seen!
microscopic plants which are usually found swimming and
floating in the sea. Organisms that live like this are called
plankton, and those that are plants are called phytoplankton.
Like most plants, phytoplankton are able to convert the sun’s
energy into food through a process called photosynthesis, so
to survive they are only found in the upper layers of the sea
and lakes where sunlight can penetrate.
If blue light is more effective than others when it comes to
animal adaptations and the use of light in the sea, why are
fluorescent proteins (FP’s) used to produce green, red, orange,
and other colors of light?
Cnidarian biology and biodiversity
The many-colored fluorescent proteins used in this activity
originated from jellyfish and corals, related organisms that
belong to the phylum Cnidaria--stinging celled animals that
are mostly found in the ocean and include sea anemones. In
a research laboratory at UC San Diego, GFP (from jellyfish)
and dsRed (from coral) were genetically altered (mutated)
to create a library of proteins that would both absorb and
emit different wavelengths (colors) of light under different
environmental conditions. Scientists continue to research the
existence, diversity and function of FPs in nature, especially
as it relates to animal biology and ecology.
Research on the function of FPs in coral biology and health
is currently being pursued by researchers at several universities, including UCSD’s own Scripps Institution of Oceanography. Some hypotheses regarding the function of fluorescent
proteins in corals include: they act as sunscreen, protecting
the coral from the suns harmful rays; they act to convert the
energy of the sunlight into light that can drive photosynthesis; they provide a beacon to coral symbionts or other coralinhabiting microbes that can detect light.
To understand why scientists are studying these potential
functions, you may want to know more about coral biology.
The coral reef habitat is unique because it is warm, shallow,
and crystal-clear (nutrient-poor) water. Corals and anemones have a special symbiotic relationship (a relationship that
is beneficial to both species) with unicellular algae called
zooxanthellae. These organisms are dinoflagellates, a group of
A healthy reef environment.
Photo courtesy of Birch Aquarium at Scripps
APPENDIX 2 | 37
Appendix 2 - Structure determines function of fluorescent proteins
The science within GFP
Green fluorescent protein (GFP) is a barrel-shaped protein with a unique ability: when exposed to blue light, it can fluoresce green. The structure of GFP is
quite elegant. Proteins are made up of amino acids that are linked together via
an amide bond (N-C). There are 20 amino acids, and they are linked sequentially in different and distinct combinations to produce a long peptide polymer.
Each amino acid has a different side chain, which has a certain chemistry to it
that makes each amino acid different. GFP is made of 238 amino acids.
The 238 amino acids are linked together to form the basis for GFP. This sequence is called the protein’s primary structure. There is a secondary structure, dictated by the chemistry of the protein’s amino
acids’ amide bonds. Since proteins are hydrophilic, or water loving, the amino acids arrange themselves to hydrogen bond in
the most energetically favorable state with water molecules. That is to say, hydrogen bonds are formed with water molecules
to form what is called a “beta sheet”. This beta sheet can be thought of as ribbons of amino acids that stabilize themselves, via
structure, in water, through hydrogen bonding.
The sequence of the 238 amino acids is GFP’s primary structure. The hydrogen bonding by these amino acids with water
molecules is GFP’s secondary structure. Most every protein has a tertiary structure. The beta sheet of GFP folds back upon
itself to form what is called a “Beta Barrel.” This formation is again driven by the interaction of the protein with itself and the
water environment. Remember, all these amino acids have distinct side chains, and these side chains have distinct chemistries.
So in the tertiary structure, the protein folds to form a structure to make sure all of the amino acid side chains that like water
face outwardly and interact with water, and side chains that do not like water are shielded from water. So for GFP, looking at
the beta barrel illustration above, the water hating part is shielded because it is located between “ribbons”and thus, shielded
from water. The water loving part is hanging off the ribbons, interacting with water (this is an oversimplification, but generally works). As a final note, the ribbons could have folded up into any structure, but the beta barrel is the most energy efficient
structure given GFP’s primary structure (sequence of amino acids). Nature is elegant.
If you remember nothing else, just know that the GFP is a beta barrel with a chromophore protected in the center of the barrel. The chromophore in this case is formed via an interaction between amino acid #65 (Serine 65), Tyrosine #66, and Glycine
#67 that absorbs blue light and emits green, giving GFP its green glow.
You can create different chromophores to GFP and have the protein emit different colors of light. Think red, blue, green, yellow, etc., any wavelength that is visible. So the big picture goes like this:
1. You can create any visible fluorescence you want, given changing the chromophore by changing amino acids 65, 66, or 67,
or some combination of the three.
2. You can link green fluorescent proteins to other molecules.
3. You can link green fluorescent protein variant that emits color
x,y, z, etc. to any molecule.
4. Build a detector that looks for a molecule via colored light, and
now you can do some targeted science!
A simple example is DNA sequencers. DNA is made up of
A,C,T,G base pairs. Tag each molecule with green, blue, red, or yellow, and then you can determine the sequence of any DNA molecule based upon the color pattern. Link GFP to a drug that targets
cancer cells, and then inject the drug into biopsied tissue. If the drug
lights up in cancerous cells, but not normal cells, you have success.
The drug might or might not work, but at least you know the drug
is targeting the bad cells and not the good cells. The applications are
limitless.
Fluorescence image of gray fox lung fibroblast. a) Transfection b) transcription c) translation d) trafficking and localization e) incorporation
into actin filaments. Scale bar is 10 microns.
38 | BACTERIAL TRANSFORMATION USING FLUORESCENT PROTEIN
Appendix 3 - Fluorescence
light
light
Sulfur
When a substance emits light after absorbing light or other electromagnetic radiation of a different wavelength, the process is
called fluorescence. In most cases, the emitted light has a lower energy (longer wavelength). When an atom absorbs radiation,
an electron may be excited and move to a higher energy level. When that atom returns to its lower energy (or ground state), a
photon (or packet) of light is emitted (see illustration above right). This illustration shows the more simplified Bohr model of
electron orbitals, but helps demonstrate the general idea of fluorescence.
Fluorescence may also occur outside the visible spectrum, and has a wide variety of uses within many scientific fields. Many
scientific uses take advantage of fluorescence within the visible spectrum, usually caused by absorption of ultraviolet (UV)
light (see illustration above left). The growing field of fluorescence microscopy has led to many discoveries about processes
which are otherwise very difficult to visualize. Fluorescent substances can be introduced into an organism and made to fluoresce, allowing visualization of processes within cells while an organism is still alive.
Endothelial cells tagged with a variety of fluorescent
markers, viewed with a fluorescent microscope.
APPENDIX 4 | 39
Appendix 4 - Chemistry of GFP
Once you understand the general structure of GFP (see Appendix 2), it is important to understand the chemical reactions involved in making GFP glow. How is a chromophore formed? Chemically, it involves a multi-step reaction. In the illustration
below, the chromophore is shown in stick representation, with carbon in gray, oxygen in red, and nitrogen in blue. Heim et al.
(1994) suggested this mechanism for chromophore formation: after translation of the protein takes place, a series of modifications converts the serine 65, tyrosine 66, and glycine 67 tripeptide sequence into a fluorescent chromophore. The final appearance of the chromophore is show in part A. In part B, dashed lines represent connections to the polypeptide chain.
To achieve the variation in color between different chromophores, slightly different chemicals are needed. Each chromophore
shown below represents a different source or a different color:
A. Aequorea victoria’s green fluorescent protein chromophore (Shimomura, 1979).
B. Discosoma (a coral) red fluorescent protein chromophore.
C. Zoanthus (a marine mat formed of individual polyps) yellow fluorescent protein.
D. Anemonia sulcata (an anemone) fluorescent protein chromophore
E. Trachyphyllia geoffroyi (open brain coral) red fluorescent protein chromophore.
F. Two stereoisomers of fluorescent protein chromophores.