UNIT 8 NOTES – MOLECULAR BIOLOGY AND EMBRYONIC DEVELOPMENT
FROM GENES TO PROTEINS
I.
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Overview
Although all cells with a nucleus in our body contains the same genetic information but the
same set of genes may be expressed very differently at different stages in an organism’s life or
in different cells.
Mendel discovered that traits are passed from one generation to the next or could skip a
generation.
Hershey and Chase discovered that DNA is responsible for passing the genetic information on
from one generation to the next.
Archibald Garrod – as he studied alkaptonuria, he observed that some diseases are caused by
defective enzymes that stopped metabolic pathways.
Beadle and Tatum – used bread mold to cause mutations in them. Came up with the “One gene
– one enzyme hypothesis” with a set of experiments that followed the procedure below:
As more information was discovered, this hypothesis was modified to one gene only determines
one polypeptide, not necessarily a fully functioning protein.
II.
The Central Dogma of Biology
 Francis Crick created the term. According to the central dogma information is always inherited
from the DNA to the RNA to the proteins.
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DNA is considered a permanent molecule in the cell’s life while RNA is temporary and breaks
down quickly after it is used.
Different types of cells make different proteins depending on their functions. So different genes
are active in them.
Review the structure of RNA and its types (mRNA, tRNA, rRNA and siRNA)
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III.
Transcription is the process that converts the information from the DNA into RNA.
Translation converts the information from RNA to proteins.
Transcription
A. Molecular Components:
 An enzyme called RNA polymerase opens the two strands of the DNA molecule and hooks
together the RNA nucleotides as they base-pair along the DNA. RNA polymerase can only
assemble the polynucleotide chain from the 5’ → 3’ direction but they don’t need priming to
start the assembling. ONLY THE 3’
5’ DNA TEMPLATE IS COPIED.
 There are specific regions on the DNA where the assembling of the new mRNA molecule starts.
The sequence where RNA polymerase attaches and initiates transcription is the promoter. In
prokaryotes, the sequence that ends transcription is called the terminator. The promoter
region is said to be “upstream” from the terminator region. The stretch of DNA that is being
transcribed into an mRNA molecule is called the transcription unit.
B. Synthesis of an RNA Transcript:
 The three stages of transcription are: initiation, elongation and termination of the RNA chain.
 Initiation: It starts at the promoter region of a gene. This region includes the actual start point
of transcription and several dozen other nucleotides “upstream”. The promoter region binds
the RNA polymerase and determines which DNA strand will be copied. In prokaryotes the RNA
polymerase directly recognizes the promoter region and binds to it. In eukaryotes, a collection
of proteins called transcription factors mediate the binding and initiates transcription. The
transcription factors, RNA polymerase and the promoter region together are called
transcription initiation complex. The specific region of the promoter that has a set of repeating
TATA bases is called the TATA box.
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IV.
Elongation: RNA polymerase moves along the DNA molecule, it continues to untwist the DNA 10
– 20 nucleotides at a time and adds nucleotides to the 3’ end of the RNA molecule. The
nucleotides are used in a form of ATP, GTP, UTP and CTP, so energy is provided by them to form
the new bonds of the forming RNA molecule. Several polymerase molecules can transcribe the
same gene at the same time. Once the RNA molecule is ready, it peels off of the DNA molecule
and the DNA twists back again.
Termination: This mechanism is different in prokaryotes and eukaryotes. In prokaryotes, the
process of transcription continues through the terminator sequence of DNA. This sequence
makes the RNA polymerase detach from the DNA molecule and release the transcript which is
completely done. In eukaryotes, the pre-mRNA is made by the RNA polymerase but there is a
long additional sequence of polyadenilation signal (AAUAAA) and other additional nucleotides
“downstream” from the original gene that was copied. These additional nucleotides make the
proteins that were associated with the transcription fall off and the pre-mRNA released.
However, the pre-mRNA has to go through an editing process before it can be used as a
functional mRNA molecule.
RNA modification
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Alteration of mRNA ends: The 5’ end that is transcribed first gets a modified guanine nucleotide
forming a 5’ cap. The 3’ end gets additional 50 – 250 adenine nucleotides forming a poly-A tail.
The 5’ cap and the poly-A tail seem to facilitate the export of the mature mRNA from the
nucleus. They also help to protect the mRNA molecule from degradation by hydrolytic enzymes.
They also help ribosomes to attach to the 5’ end of the mRNA molecule.
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RNA splicing: the removal of a large portion of the RNA molecule by a “cut-and-paste” method.
The removed noncoding sequences of mRNA nucleotides that lie between the coding regions
are called introns. Exons are the coding sequences. The signal for cutting is a set of small
sequences of nucleotides that are recognized by small nuclear ribonucleoproteins (snRNP’s or
“snurps”). These snurps join with other proteins to form a spliceosome – molecular units that
cut introns out and attach exons to each other.
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The consequence of DNA splicing is that a single gene can encode more than one kind of
polypeptide. Depending on which segment of the gene is treated as an exon, it can give rise to
multiple polypeptide – alternative RNA splicing.
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Great, detailed movie on transcription: http://vcell.ndsu.nodak.edu/animations/transcription/movie.htm
Same site on RNA processing: http://vcell.ndsu.nodak.edu/animations/mrnaprocessing/movie.htm
http://highered.mcgrawhill.com/sites/0072507470/student_view0/chapter3/animation__mrna_synthesis__transcription___quiz_
1_.html
RNA splicing: http://www.sumanasinc.com/webcontent/animations/content/mRNAsplicing.html
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V.
The Genetic Code
 Translation is the process of converting information from mRNA into proteins.
 The information on the mRNA molecule is read in 3 nucleotide sequences called codon.
 All codons and what amino acids they determine is included in a table of codons. This table also
includes 1 start codon (AUG) that codes for methionine amino acid and starts the synthesis of
every polynucleotide chain. 3 stop codons are also included on the table. If these codons are
reached, the translation process will stop even if there is some more mRNA remains.
 The genetic code is nearly universal to all known species on the planet – another evidence of the
uniform origin of life.
 Once the mRNA code is being read, every nucleotide is only part of one codon and the reading
of codons is continuous, no leftover nucleotides between codons.
VI.
Translation
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Transfer RNA (tRNA): Its function is to transfer amino acids from the cytoplasmic pool of amino
acids to a ribosome. The tRNA molecules are not identical. Each tRNA molecule attaches to a
specific mRNA codon and carries a specific amino acid that matches that codon. One end of the
tRNA molecule is attached to a specific amino acid while the other end has a nucleotide triplet
called anticodon that is complementary to the codon of the mRNA molecule.
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Ribosomes – Small organelles that attach the proper tRNA molecules with the mRNA codons.
Ribosomes are made up of two subunits that are made in the nucleus of eukaryotes from
proteins and ribosomal RNA (rRNA). The large and small subunits bind only when they are
attached to an mRNA molecule. Prokaryotic ribosomes are smaller and lighter than eukaryotic
ones. Each ribosome has a binding site for the mRNA molecule and three binding sites for tRNA:
P site (holds the tRNA carrying the growing polypeptide chain), A site (holds the tRNA carrying
the next amino acid to be added to the polypeptide chain) and E site (the site that releases the
tRNA molecule.
A. Building a Polypeptide:
 Ribosome association and initiation: This stage brings together mRNA, a tRNA bearing the first
amino acid and the two subunits of a ribosome. First the small subunit binds with the mRNA
and the tRNA molecule that brings methionine. The small subunit than moves downstream
along the mRNA until it reaches the start codon. Once the tRNA binds to the initiation codon
with hydrogen bonds the large subunit also attaches to the small subunit. Proteins called
initiation factors are also important for this process. Energy is provided by GTP molecules.
 During elongation amino acids are added one at a time. Each addition involves the participation
of several proteins called elongation factors.
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Elongation continues until a stop codon on the mRNA molecule is reached on the A site of the
ribosome. A protein called a release factor binds to the stop codon and causes the addition of a
water molecule instead of another amino acid to the polypeptide chain.
A single mRNA molecule can be used to make many copies of a polypeptide simultaneously
because several ribosomes can work on the same mRNA molecule. These strings of ribosomes
are called polyribosomes or polysomes.
B. Modifications of the polypeptide chain:
 During the translation, the polypeptide chain begins to fold into its 3D shape. Additional steps
may be required such as adding carbohydrates (glycosylation), lipids, phosphate groups
(phosphorylation) to some amino acids.
 One polypeptide chain can be cut into multiple pieces or more than one polypeptide chains can
come together to form a functional protein.
 Some proteins are made in a form of an inactive precursor and activated only if some parts of it
are cleaved off – used in some enzyme activations.
 There are two types of ribosomes available. One type is free moving in the cytosol, the other is
attached to the ER or to the nuclear envelope. Free ribosomes synthesize proteins that are free
moving in the cytosol. Membrane-bound ribosomes make proteins of the endomembrane
system and proteins that are released for secretion. However, both types start out as free
ribosomes and attach the rough ER only during the translation process when certain signal
molecules make it.
 Western Blot – is a technique that is used to identify particular proteins in a cell or tissue
sample. Steps of this method:
o First proteins are separated by using gel electrophoresis by size.
o Next, the gel with the separated proteins is transferred to a blotting paper. The paper
absorbs the proteins in the same pattern as they were in the gel. This is the blot
o The paper than blocked by inactive proteins
o To look for one specific protein of interest on the blot, an antibody is added that will
only bind to the specific protein. Than a secondary antibody is added that binds to the
primary antibody. This secondary antibody will bind to a dye molecule or some other
substrate that makes the protein visible on the blot paper.
Animation: http://www.dnatube.com/video/1511/Western-blot
PROKARYOTIC GENE EXPRESSION
As a related topic please review bacterial genetic recombination including transformation, transduction
and conjugation
I.
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Gene Regulation in Bacteria
In bacteria transcription and translation are not separated by a barrier. In fact, these two
processes can take place at the same time. As soon as part of an mRNA is copied it can be
translated into a protein.
Also, RNA modification does not occur in bacteria
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Bacterial genes are organized into operons – a sets of genes that are transcribed together under
one regulatory unit of an operator and a promoter. These genes determine proteins that are
part of the same metabolic pathway.
 Promoter – is the region of the DNA that RNA polymerase binds with and transcription factors
also attach to it to start transcription.
 Operator – a specific sequence within the DNA that binds transcription factors to turn
transcription on or off. It is found within the promoter or between the promoter and the coding
region.
 An operon = promoter + operator + coding genes
II.
Repressible operons
 Repressible operons usually have their transcription on and they are repressed by a small
molecule that binds allosterically to a regulatory protein.
 Repressible operons produce important molecules such as certain amino acids that are
necessary to build macromolecules. If the final product (such as an amino acid) is available in
the environment, the bacterium does not need to produce it so it shuts down (represses) the
operon that results in the important molecule.
 When the operon is working (not repressed), the RNA polymerase can bind to the promoter
region, slide along the operator and copy the five genes for five different polypeptides to make
the enzymes of the tryptophan making metabolic pathway.
 During the working condition of the operon, there is an inactive repressor protein in the cell.
This repressor protein cannot bind alone to the operator so it just remains inactive.
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When tryptophan is available in the environment, the bacterium takes it in and uses it. In this
case the bacterium does not need to make tryptophan. One of the tryptophan molecules binds
with the repressor protein and activates it. This active repressor binds to the operator and acts
as a roadblock to the RNA polymerase. The polymerase cannot transcribe the gene so mRNA is
not produced.
http://highered.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120080/bio26.swf::The
%20Tryptophan%20Repressor
III.
Inducible Operons
 These operons are usually turned off and the genes are not being actively transcribed.
However, these genes can become active when an allosteric activator (effector) is introduced
into the cell.
 For example, bacteria usually don’t use lactose as a source of sugar, so they don’t have enzymes
to digest it. However, if lactose is introduced in the environment, they can activate genes to
produce lactose digesting enzymes.
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So when the operon is turned off, a repressor protein is attached to the operator and does not
allow transcription of RNA molecules.
When the bacterium finds lactose in the environment and eats it, one of the lactose molecules
can bind with the repressor and detach it from the operator. As the roadblock is removed, the
RNA polymerase can move along the gene and transcribe RNA molecules to make enzymes to
digest lactose.
Once the lactose is used up the repressor becomes active again and attaches back to the
operator and stops transcription.
https://highered.mcgraw-hill.com/sites/dl/free/0072835125/126997/animation27.html
EUKARYOTIC GENE REGULATION
I.
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Mechanisms of Gene Regulation in Eukaryotic Cells
Cell differentiation – multicellular organisms have very different cells with a wide range of
shapes and functions. They all contain the same DNA but different genes are turned on or off in
each. The process of cell differentiation turns some genes on and others off.
While prokaryotic gene regulation is mostly determined by environmental factors and involve
activators, repressors and operons; eukaryotic gene regulation can occur in different stages and
can occur for many different reasons.
The following table is a great review of the different stages at which gene regulation can take
place:
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II.
Regulation of Chromatin Structure:
Heterochromatin -- tightly packed parts of chromatin that stains dark under the microscope. Genes
here are usually not expressed.
Euchromatin -- part of the chromatin that is more loose and usually holds actively transcribing genes
Histone acetylation -- acetyl groups can be attached to histone proteins to prevent the histones to
bind with each other and tightly pack up. As a result, the chromatin remains lose and easily
transcribed.
Histone methylation -- methyl groups (-CH3) are attached to the histone tails. This promotes the
condensation (close packing) of the chromatin and makes it less active.
DNA methylation -- enzymes can also methylate certain bases of the DNA molecule. The
methylated sections of DNA are usually not transcribed. This can lead to long-term inactivation or
genomic imprinting -- the inactivation of the mother's or father's genes in diploid cells at the start of
development.
Epigenetic inheritance -- the modification of the chromatin can be inherited although these
modifications do not change the nucleotide sequence of the DNA. These modifications however,
can also be reversed. Epigenetic inheritance is changes in the phenotypic expression of a trait, but
this change is not due to changes in the DNA sequence. Other examples: all of what comes in these
notes, Barr body deactivation, lac operon in bacteria, Trp operon in bacteria.
III.
Regulation of Transcription Initiation:
 In a eukaryotic genes can be turned on or off during the initiation of transcription. The
complete initiation complex (several transcription factors and RNA polymerase II) have to be
assembled on the promoter region of the gene to initiate transcription. If only a few general
transcription factors bind to the TATA box, only a few mRNA molecules will be produced. To
have high efficiency translation performed, several specific transcription factors need to be
attached to the promoter region.
 The enhancer region can also improve the efficiency of transcription if activator proteins bind to
the enhancer region and those make the enhancer region bind to proteins of the transcription
initiation complex. As a result, the transcription can occur faster, more efficiently.
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Some specific transcription factors can also function as repressors to inhibit expression of a
particular gene. These repressors can prevent the binding of activators or other transcription
factors to the promoter region.
http://www.hhmi.org/biointeractive/regulation-eukaryotic-dna-transcription
IV.
Mechanisms of Post-Transcriptional Regulation
Transcription alone will not result in gene expression. To have a functional protein, many things need to
take place after the pre-mRNA is made. Any one of the steps of making a functional mRNA or a
functional protein can be shut down or sped up as part of gene regulation. The following are a few
examples of these regulatory processes:
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RNA processing – Alternative RNA splicing is a good example of a way to form different mRNA
molecules.
mRNA degradation – mRNA has a limited life span to form proteins. Prokaryotic mRNA can be
broken down within minutes after transcription. In eukaryotes, however, mRNA can survive
longer, sometimes for weeks. This degradation of mRNA can be done by enzymes gradually
breaking down the 5’ cap, poly-A tail than the entire segment of mRNA. Small segments of RNA
molecules (microRNA’s or miRNA) can also attach to the mRNA and prevent translation or can
actually break down the mRNA.
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Initiation of translation – regulatory proteins can bind to mRNA and prevent it to bind with the
ribosome during the initiation of translation
Protein processing and degradation – To activate proteins, they need to be modified by either
cleavage of certain parts off (pepsinogen to pepsin) or by attaching phosphate groups to the
protein (protein kinase receptors). Regulatory proteins can stop any of these steps and can
make proteins dysfunctional.
Quiz 1 is on the notes up to this point.
EMBRYONIC DEVELOPMENT
I.
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Stages of Embryonic Development
Embryonic development describes the earliest stages of development after fertilization. Some
of the steps of embryonic development are similar is all animals.
The initial stage is fertilization – the process in which gametes, the egg and sperm fuses
together to form a zygote.
The zygote than undergoes a series of mitotic cell divisions without growing this process is called
cleavage. Cleavage forms a structure called the blastula -- a hollow ball with cells only on the
outside.
The next phase is called the gastrulation – during this process one side of the hollow ball moves
inside and creates first two than later three tissue layers. This form of the embryo is called the
gastrula. The tree tissue layers are the ectoderm (outer layer), mesoderm (middle layer) and
endoderm (inner layer)
The three tissue layers eventually give rise to the various organs during organogenesis.
Although different species have different body plans, they follow very similar developmental
steps.
II.
Fertilization
 During fertilization, an egg and a sperm fuse together to form a zygote. Each gamete has half
the typical number of species, so when they fuse, the typical chromosome number of diploid
cells is restored.
 The sperm uses enzymes to dissolve some of the egg’s outer coating. These enzymes are in the
acrosome of the sperm’s head. Both the egg and the sperm cell membrane has specialized
receptors. Once these receptors bind, they start to fuse together. If more than one sperm fuses
with an egg, polyploidy occurs that is not a viable condition in animals.
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Once the receptors of each cell bind, the plasma membranes of these cells fuse together and
the sperm nucleus enters the egg. At the same time, sodium ion channels open on the egg cell
membrane and sodium ions move into the egg, decreasing the membrane potential of the egg.
This depolarization prevents other sperm cells from entering the egg. Vesicles inside of the egg
cytoplasm are also activated to merge with the cell membrane of the egg. These vesicles
release enzymes that separate the outer coating of the egg from the cell membrane forming a
thicker, protective layer. This layer also prevents other sperm cells from entering – cortical
reaction
Finally the genetic material of the egg and sperm combine.
http://www.youtube.com/watch?v=_5OvgQW6FG4
Interesting discussion: http://www.sciencefriday.com/playlist/#play/segment/7931
III.
Cleavage
 After fertilization, the zygote undergoes a series of mitotic divisions called cleavage. This
process initially results in a large number of cells that are very small in size. These fast divisions
continue until a blastocoel an asymmetrical cavity forms inside the zygote. At this point we call
the structure a blastula.
http://www.hhmi.org/biointeractive/human-embryonic-development
IV.
Gastrulation and Germ Layers
 Gastrulation and the development of germ tissue layers influence cell and tissue arrangement
and the shape of the animal’s body.
 During gastrulation three tissue layers, the ectoderm, mesoderm and endoderm form. The
following organs form from these layers:
o Ectoderm – exterior of the body such as skin but also forms the central nervous system
o Mesoderm – forms the muscles and bones
o Endoderm – forms the internal organs such as lungs, digestive system parts
http://www.hhmi.org/biointeractive/differentiation-and-fate-cells
 At this stage, cells clearly start to differentiate and move to various positions to form the
animal’s body plan.
 As the gastrulation completes, the neural tube starts to form. This tube becomes the central
nervous system.
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Once the central nervous system is in place, organogenesis – the formation of organs occurs.
The first organs that develop are the brain, spinal cord and related structures. Than the heart,
lungs and other organs continue. The lungs are not functioning until birth and many of the
other organs will continue to develop until later stages of development.
http://www.hhmi.org/biointeractive/development-human-embryonic-brain
V.
Morphogenesis
 Morphogenesis – the process that encompasses developmental processes that involve cell
movements to specific locations, cell maturation to perform a particular function.
 Two main forces direct morphogenesis:
o Autonomous specification – various regulatory proteins within the cell influence the cell
to mature and specialize. These regulatory proteins are produced by active genes
within the cell.
o Conditional specification – involves external signal molecules and cell signaling
pathways and other growth factors to turn on cell machinery (various developmental
genes) to change the cell into its mature form.
 Many of these processes can only take place if three main axes are determined and the body
has particular regions assigned. These regions include the anterior-posterior (front and back)
axis, medial-lateral axis (middle/left, right), dorsal-ventral axis (stomach area and back area).
These directions will initiate the production of specific proteins by specific genes, ex. Dorsal
gene of the fruit fly moves proteins into the ventral area, so if the gene is broken only the dorsal
side of the animal develops properly.
 Morphogens – signaling molecules that trigger autonomous specification but also can trigger
nearby cells to differentiate. Morphogens seem to move in one direction from one cell to the
next by one. This way the concentration of morphogens is gradually decreasing as we move
away from the releasing cell. A well-known morphogen called the sonic hedgehog homolog
influences the production of transcription factors needed for cell differentiation while
suppressing other transcription factors.
 Hox genes – specific genes that determine the body plans of the animal (such as the location of
various parts of the body).
http://www.pbs.org/wgbh/evolution/library/03/4/quicktime/l_034_04.html
I. Understanding and Manipulating Genomes
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Biotechnology is a booming field of science with constantly improving technology and new
discoveries weekly.
Some key terms to know:
o Recombinant DNA – DNA in which nucleotide sequences from two different sources, often
different species, are combined in vitro into the same DNA molecule.
o Genetic engineering – the direct manipulation of genes for practical purposes
o Biotechnology – the manipulation of organisms or their components to make useful products
(from wine and cheese making to analyzing personal genomes and fixing mutations)
Radiolab: http://www.wnyc.org/flashplayer/player.html#/play/%2Fstream%2Fxspf%2F92351 –
35:00 min
II. DNA Cloning
A. The Method of DNA Cloning:
 Gene cloning – methods for preparing well-defined, gene-sized pieces of DNA in multiple
identical copies.
 Most commonly bacteria and their plasmids are used:
o Plasmid is isolated
o Foreign DNA is inserted into the plasmid – recombinant DNA
o Plasmid is returned into the bacterium
o Bacterium reproduces to form clones of identical cells
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Cloned bacteria can make many copies of a certain gene and can produce certain proteins.
B. Using Restriction Enzymes:
 Restriction enzymes – enzymes that cut DNA molecules at a limited number of specific
locations. In nature, these enzymes protect the bacterial cell against intruding DNA from other
organisms, by cutting this DNA segments up.
 Restriction sites – short segments of DNA that are recognized by the restriction enzyme.
 The bacterium’s own DNA is protected by methylation from restriction enzymes.
http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter16/animations.html#
C. Cloning a Eukaryotic Gene in a Bacterial Plasmid
 The original plasmid is called a cloning vector – this plasmid has the ability to carry foreign DNA
into a cell and replicate it there. Bacterial plasmids are widely used cloning vectors, because
they are easy to isolate, manipulate and can be reintroduced back into the bacterium after
isolation. Because bacterial cells reproduce quickly, the inserted gene or its proteins can be
obtained in large quantities. Use: http://highered.mcgrawhill.com/sites/0072437316/student_view0/chapter16/animations.html#
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After genes are inserted into bacteria by using DNA cloning, the success of the experiment can
be analyzed by two methods:
a. Looking for the inserted gene in the bacterial colonies
b. Looking for the synthesized proteins in the new bacterial colonies
Nucleic acid hybridization – is the process that detects certain sequences of the DNA molecule
by using nucleic acid probes that are radioactively labeled. These probes can bind to denatured
DNA molecules (two strands of DNA separated) and radioactively label the colonies that contain
the inserted gene.
Animations:
DNA cloning: http://www.sumanasinc.com/webcontent/animations/content/plasmidcloning.html
III. THE POLYMERASE CHAIN REACTION (PCR)
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When the source of DNA molecule is impure or there is only a small amount of DNA present, PCR is
the most effective way to amplify one or many segments of DNA.
This method can make millions of copies of a segment of DNA in a few hours.
PCR is a three-step cycle that brings about a chain reaction that will produce an exponentially
growing number of copies of identical DNA molecules.
Steps:
a. first the target sequence is denatured (separated to individual polynucleotide
chains) by heat
b. second, cooling allows short segments of DNA primers to attach by hydrogen
bonding at the 5’ → 3’ direction
c. Heat-stable DNA polymerase is used to assemble the nucleotides of the new
strands
Animations:
PCR -- http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter16/animations.html#
http://www.dnalc.org/ddnalc/resources/pcr.html
PCR song:
http://bio-rad.cnpg.com/lsca/videos/ScientistsForBetterPCR/
I.
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GEL ELECTROPHORESIS
This process uses a gel to separate various segments of DNA molecule or protein based on their
size and electrical charge.
A mixture of DNA segments of different sizes can be injected into the wells of the gel than put in
an electric current. The electric current is running from the – to the + electrode and drags the
molecules with it.
The smallest pieces of molecules run the furthest. A fluorescent dye can be used to dye the
DNA segments and make them visible.
Gel electrophoresis can be used to locate mutations on various DNA molecules, separate certain
segments of DNA from the others for further examination, purify DNA, the band pattern can
help in identifying a person etc.
Interactive lab: http://learn.genetics.utah.edu/content/labs/gel/
Animation:
http://www.dnalc.org/ddnalc/resources/electrophoresis.html
II.
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SOUTHERN BLOTTING
This technique combines gel electrophoresis and DNA hybridization to allow researchers to find
a specific human gene. It can be used to identify individual nucleotide differences (mutations) in
the DNA molecule. It can also compare particular DNA fragments from different sources that
were digested by restriction enzymes.
http://highered.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120078/bio_g.swf::Sout
hern+Blot