Name ______________________
Lab Partner _________________
This is the Yeast of Your Problems:
The effects of media components on Saccharomycescerevisiae
Summary
Students will design and prepare a growth medium for the culture of the yeast, Saccharomyces cerevisiae.
In doing so, they will reflect on the nutrient requirements of eukaryotic cells, on how they obtain these
nutrients, and which essential molecules can be synthesized and which must be provided to them. They will
culture the yeast and compare their media with the commercial medium, Yeast Extract Peptone Dextrose.
The students may also design an experiment to test the effects of removing, or changing, a single
component of their media. The students will utilize their experiences to identify the difficulties presented to
scientists attempting to culture mammalian cells and examine the culture media used to culture HeLa cells,
the first human cells to be grown in tissue culture.
This activity may be used with many units throughout the biology curriculum, specifically the
characteristics of living things, cell chemistry, cell biology, cell respiration, the use of energy, digestion,
literacy in science in conjunction with the text "The Immortal Life of Hennrietta Lacks".
This lab may also be used as a long term science activity combinined with other yeast and biotechnology
experiments and computer applications (BLAST).
Background
Saccharomyces cerevisiae, more commonly known as baker’s yeast, is a singled celled eukaryote organism.
Yeast has long been studied in labs, it is considered a model organism. Normal cell division is central to
normal growth and development in all cells. Human versions of a number of yeast cell cycle and DNA
repair genes have been found to be directly involved in human cell division. Malfunctions in either of these
processes can lead to cancer or birth defects. The normal activity of these genes are studied in yeast cells,
which are easily manipulated in the laboratory. This provides important insights into how these genes work
in humans. In order to study cells the cells must be given nutrients as well as an environment conducive to
growth. The substance that provides this is media.
Purpose
You will determine the components that media must include and describe why these components are vital
to the yeast and allow the yeast to survive and thrive. You will also determine the effect of the different
media components on growth and survival of Saccharomyces cerevisiae. You will design and prepare your
own media, grow yeast on your media and compare growth, survival, and morphology of the yeast to that
of yeast grown on commercially prepared defined media presenting your findings to your classmates.
(Variation: have students design media with different groups leaving out one major component of media,
prepare the media, plate the media, then compare growth of your media to that of the yeast grown on
commercially prepared defined media and present result to the class).
Objectives
Upon completing this project, students will
1.
identify
i.
the major macromolecules found in yeast cells as well as the structure and function of
these molecules.
ii.
the major nutrients required by yeast cells.
iii.
the major nutrients supplied by the media used to culture HeLa cells.
2.
design and prepare a growth medium for yeast.
3.
culture yeast on agar plates, comparing the growth and morphology of the yeast with those
cultured on YPD plates.
4.
experimentally determine the effects of removing, or changing , one of the components of their
culture media.
Materials: Overnight culture of S. cerevisiae Permanent marker
YPD Plate Agar
Pipets Glucose
“Hockey stick” spreader Fructose
Sucrose Albumin
Dried milk powder Baby formula
Salt-free beef broth Soy protein
Vitamin, mineral supplement Sea salt
Peptone Whey
Procedure:
Part I. Introductory Questions
Work with your partner to write your ideas for the following: Be prepared to discuss your ideas in class.
1.
2.
3.
What are the basic macromolecules found in yeast?
How do yeast normally obtain these molecules?
What additional nutrients may be required by yeast?
Part II: Designing your media
Work with your partner to write your ideas for the following: Be prepared to discuss your ideas in class.
4.
5.
6.
7.
How will your yeast obtain nitrogen, phosphorous and minerals, such a s Ca++?
Will your yeast be able to digest the proteins, carbohydrates, etc. that you are supplying to them?
How will you adjust the pH of your media? Will you use a buffer?
How will you adjust the tonicity of your media?
8.
Fill out the form provided to you for your yeast media formula.
i.
Choose from the following for your media:
a. Carbohydratess
a. Glucose, sucrose, fructose
b. Proteins
a. Albumin, soy protein, egg white, peptone, dried milk, powdered baby
formula, salt-free beef broth or beef extract
c. Salts
a. NaCl, sea salt, etc.
d. Vitamins and minerals
9.
What should be the pH of the media? How will you adjust the pH of your media? Will you use a
buffer?
10. How will you adjust the tonicity of your media
Part II: Comparison with Yeast Extract Dextrose (YED) media
Part II: Preparation and testing of student media.
11. Prepare your media.
i.
Check the pH.
12. Grow yeast on your media and on YED media. Follow the directions given to you by your teacher.
Compare:
i.
Growth rate
ii.
Colony morphology
iii.
Cell morphology
Note: In this experiment an hypothesis is not important. You are trying to develop
simple, defined, media for the culture of yeast cells. You will be comparing the growth
of the yeast cells cultured with your medium with those cultured with commercially
available YPD medium. Your goal is to be able to grow healthy yeast cells using your
medium.
Part III: Comparison of Your Media with Yeast Extract Dextrose (YED) media
13. Compare your media with commercial Yeast Extract Dextrose media.
Work with your partner to write your ideas for the following: Be prepared to discuss your ideas in class.
i.
ii.
iii.
How are they similar?
How are they different?
Why do you think that some nutrients were provided in a different, or more complex
form, such as peptone and yeast extract?
iv.
v.
What is peptone? Why is it used in some culture media?
Do you want to make any changes to the composition of your media? Describe why you
would make these changes.
Extension 1:
14. Look at culture media designed for mammalian cells, as described in “The Immortal Life of
Henrietta Lacks”..
i.
Read excerpt for “The Immortal Life of Henrietta Lacks”.
a. What was used as culture media for the HeLA cells?
b. Discuss the reason for each ingredient used.
c. Why do you think that such undefined components are used?
d. Describe and support with examples from the text what you think the greater
challenge to scientists in tissue culture at the time-technology or the lack of
appropriate and standard cell growth media.
ii.
What is serum?
a. What is in serum?
b. Why is this important for mammals and not for yeast?
IMPORTANT: Be sure to WASH HANDS Before AND After working with S. cerevisiae
AND to wear goggles.
Variation Procedure for culturing yeast cells.
Student Experiment
Meet with your group members and share your hypothesis and experimental plans. As a group collaborate
to develop a hypothesis and experimental plan that YOU will carryout to determine the effect media on the
growth, tonicity, and colonization and survival ofS.cerevisiae.
Hypothesis:
You may only have ONEindependent variable. To help make this process easier list your
variables FIRSTthen write your hypothesis.
Independent variable (what you change):
Dependent variable (what you measure):
Control variables (what you keep the same):
Hypothesis:
***** STOP here and obtain teacher approval before continuing.****
Procedure:
Write a procedure (step by step) for your experiment. Include how you will set it up, what materials you
will use, and how many trials you will do.
Data Table:
Construct a data table, chart, or graph to organize the data you will collect.
**** STOP here and obtain teacher approval before continuing.****Experiment
Carry out your experiment and collect your data.
Observations & Questions:
Obtain your group’s YPD plate which contains your culture of S.cerevisiae. Sketch the plate with your
media and sketch the plate with commercially prepared defined media. Describe what you observe on the
plate and write down any questions you may have.
Analysis/Conclusion:
Each group member will write a paragraph concluding your lab. Include the following:
•
Was your hypothesis supported by the data?
•
How could you improve your experiment? (Were there any sources of error?)
•
What new questions or ideas do you have?
Each GROUP will make and present a mini-poster to report their findings to the class. This will
include:
•
Title
•
Methods/Procedure
•
Data
•
Analysis and Interpretation of Data
Assessment:
-Students will be assessed based on brainstorm and modified brainstorm which should show demonstration
of objectives.
-A prelab quiz with terminology and basic concepts (depending on what topics the lab is used for)
-Data collection and analysis
-Lab questions
-Student presentation of findings and application of key concepts.
-Homework assignment reviewing macromolecules
Key Concepts: (may be modified or adjusted as to time, material covered, and depth of topic)
•
Charicteritics of living things
•
Scientific Method
•
Structure and function of Macromolecules
•
Cell biology
•
Metabolism and Respiration
•
Energy
•
Digestion
Topics to discuss may also include
how cells grow inside and outside the body (in vitro and in vivo)
how drugs, diseases, and mutations are investigated
challenges that have faced scientists (reference The Immortal Life of Henrietta Lacks)
role of technology and how advances in technology lead to advances in science
genetic components -BLAST
What do
YEAST CELLS
Need to STAY ALIVE