Genetic variation and biotechnology

GENETIC VARIATION

IN VIRUSES

UNIT 6.3 GENETIC VARIATION & BIOTECHNOLOGY

Use the information on the slides to take notes and to complete the following in your notebook:

1. Create a concept map explaining how viruses are categorized according to their genome.

2. Create a flow diagram explaining the flow of genetic information in retroviruses.

3. Explain why viruses have a high rate of mutation.

4. Research a DNA and an RNA virus that cause human diseases. Provide information about their type (spherical, helical...), how they infect their host, the diseases they cause, and their prevention.

Genetic Diversity of Viruses

●There is a huge variety of viruses that exist, but
they can be broadly categorized by the type of
genetic material they carry.

○There are DNA virus that carry either
single-stranded DNA (ssDNA) or
double-stranded DNA (dsDNA)

○There are RNA viruses, that carry either
single-stranded RNA (ssRNA) or
double-stranded RNA (dsRNA).

Flow of Genetic Information in Retroviruses

●A retrovirus is a type of RNA virus that
inserts a copy of its genome into the DNA
of the host cell that it is infecting.

●To accomplish this, the virus’ RNA
genome must be converted into DNA.

○This is accomplished by an enzyme
that retroviruses carry, called reverse
transcriptase.

●The DNA can then be integrated into the
host cell’s chromosomes, and will
ultimately be transcribed and translated
for the assembly of new viral progeny.

Genetic Variation in Viruses

Viruses evolve quickly, and often faster than their hosts. How?
1.Viruses, just like cells, can acquire mutations.

○Just like other cells, a large majority of these mutations occur from
mistakes that are made when their genomes are replicated inside host
cells.

○DNA viruses are replicated using the cell’s DNA polymerase enzymes,
which have proofreading functions.

○RNA viruses must use their own special enzymes called RNA-dependent
RNA polymerases to make copies of their genetic material. These
polymerases generally do not have a proofreading function and end up
making many more mistakes as a result. Thus, RNA viruses generally
mutate much faster than DNA viruses.

Genetic Variation in Viruses

2.

Viruses reproduce very quickly,
and with high mutation rates,
many new genetic variants can
arise just from mutations alone.

3.

Viruses can also undergo
recombination, a process that
happens when similar viruses
infect the same cell and their
genetic material ends up
packaged together in new
viruses being made.

○Ex: influenza viruses.

BIOTECHNOLOGY

UNIT 6.3 GENETIC VARIATION & BIOTECHNOLOGY

Use the information on the slides to take notes and to create a concept map explaining each biotechnology tool:

1. PCR

2. Gel electrophoresis

3. Bacterial transformation.

4. DNA sequencing.

Remember that the "stars" indicate important information to be written in your notes!

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●Genetic engineering
techniques can be used to
analyze and manipulate DNA
and RNA. These include:

○Polymerase Chain
Reaction (PCR)

○Electrophoresis

○Bacterial Transformation

Biotechnology

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Polymerase Chain Reaction (PCR)

●Polymerase chain reaction (PCR) is a widely used method that rapidly makes
millions to billions of copies of a specific DNA sample in a test tube.

○This allows a very small sample of DNA to be amplified to a large enough
amount to study in detail.

●PCR requires the following components: the DNA sample to be amplified; DNA
primers, DNA nucleotides, and Taq polymerase.

○Taq polymerase is a thermostable polymerase isolated from a
heat-tolerant bacteria (Thermus aquaticus). It is able to function without
denaturing at high temperatures.

●PCR involves repeated cycles of heating and cooling that allow DNA to be
synthesized.

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Polymerase Chain Reaction (PCR)

●The basic steps of PCR are:
1.Denaturation (96°C): Heat the reaction to
separate, or denature, the DNA strands.
This creates single-stranded template DNA.

2.

Annealing (55°C): Cool the reaction so the
primers can bind to their complementary
sequences on the single-stranded template
DNA.

3.

Extension (72°C): Raise the reaction
temperatures so Taq polymerase extends
the primers, synthesizing new DNA strands.

4.

Repeat!

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Polymerase Chain Reaction (PCR)

PCR

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Gel Electrophoresis

●Gel electrophoresis separates molecules by their size
and charge.

○Type of molecules that can be used in
electrophoresis: DNA, RNA, and proteins.

●Molecules are “loaded” into wells in the gel. Then an
electrical current pulls the molecules through the gel.

●Molecules will travel in the gel at different speeds (thus
taking them different distances) based on their:

○Size: smaller molecules travel faster than larger ones

○Charge: stronger charged molecules travel faster
than weaker charged molecules

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Gel Electrophoresis

●In DNA gel electrophoresis, DNA samples are
cut using restriction enzymes before being ran
through a gel, producing DNA fragments of
different sizes.

●Restriction enzymes are proteins that cut DNA
at specific sequences, called restriction sites.

○Ex: The restriction enzyme EcoRI cuts at
the restriction site: GAATTC

●DNA is pulled towards the positive cathode,
because DNA is negatively charged. Smaller
DNA fragments travel further than larger
fragments.

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Gel
Electrophoresis

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Gel Electrophoresis

●One application of DNA gel electrophoresis is to determine what alleles are
carried by an individual (their genotype).

●Different alleles for a gene can have different restriction sites that produce
different sets of fragments when cut by restriction enzymes.

Allele 1

Allele 2

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Bacterial Transformation

●Bacterial transformation
introduces DNA into bacterial
cells.

●Recombinant DNA plasmids
can be made to introduce new
genes into bacteria.

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Bacterial Transformation

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Adding GFP Gene to Recombinant Plasmid

DNA Sequencing

●DNA sequencing determines the order of nucleotides
in a DNA molecule. There are several techniques, but
the Sanger sequencing technique is the simplest.

●This technique requires special “chain-terminating”
nucleotides called dideoxynucleotide triphosphates
(ddNTPs), which are missing the important 3’ hydroxyl
group needed to make a phosphodiester bond with
other nucleotides.

○Normal DNA nucleotides are called
deoxyribonucleotides triphosphates (dNTPs),
which are assembled together by DNA polymerase
to synthesize a DNA strand.

Terminates synthesis

Extends DNA strand

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DNA Sequencing

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