Mutations and Viruses
Essential Questions:
What are the different types of mutations?
What are the effects of changes in the DNA code?
What causes these changes in DNA?
How do viruses play a role in mutation and knowledge
of DNA?
Remember…
The Central Dogma of Cell Biology
From gene to protein
aa
aa
transcription
DNA
aa
translation
aa
protein
mRNA
aa
aa
aa
ribosome
A C C A U G U C G A U C A GU A GC A U GGC A
tRNA
nucleus
cytoplasm
aa
trait
What are Mutations?

Any change to the Nitrogen Bases
(“letters”) in DNA are called mutations
change the DNA
 changes the mRNA
 may change protein
 may change trait

DNA
TACGCACATTTACGTACG
mRNA
AUGCGUGUAAAUGCAUGC
protein
aa aa aa aa aa aa aa
trait
Types of Mutations:
• Point mutation: change in a single base
pair in DNA (substitution)
THE DOG BIT THE CAT
 THE DOG BIT THE CAR

Point Mutations typically only affect 1 amino acid in the protein…
Causes no change in the function of the protein or
Partial function of the protein. (Example: Sickle Cell Anemia.)
Missense mutation =
changes amino acid
Missense mutation =
changes amino acid
This is due to the “Wobble” in the DNA code!
Silent mutation = no
change in protein
Nonsense mutation =
change to STOP
Your Turn!
• Look at the following sequence of Amino acids.
What type of mutation is this?
Check your
Answer
• Point Mutation, Missense
Your Turn!
• Look at the following sequence of Amino acids.
What type of mutation is this?
Check your Answer
• Point Mutation, Nonsense
Your Turn!
• Look at the following sequence of Amino acids.
What type of mutation is this?
Check your Answer
• Point Mutation, Deletion
Types of Mutations
• Frameshift mutation: a single base pair is
added or deleted and shifts the reading of the
codons.
– Adding a base is called an insertion.
– Removing a base is called a deletion.
Your Turn!
• Look at the following sequence of Amino acids.
What type of mutation is this?
Check your Answer
• Frameshift Mutation, due to a Deletion
Frameshift Mutations affect many amino acids in the protein…
Causes a non-functional protein.
(Example: Phenylketenuria PKU.)
Types of Mutations
• Chromosomal mutations: any change in the
structure or number of chromosomes,
common in plants, dangerous in humans.
deletion: part of a chromosome is removed
 duplication: part of a chromosome is repeated
 inversion: part of a chromosome breaks off and
is reinserted backwards
 insertion and translocation: part of a
chromosome breaks off and attaches to another
chromosome

Examples of chromosomal
mutations
deletion
duplication
inversion
translocation
12.4
What causes DNA to Mutate?
• There are various ways to create
a change in the genetic code.
– Some can mutate certain bases or
genes.
– Some can turn on the wrong
expression of certain genes.
• Keep in Mind, there are 3
possible outcomes for a mutation
in a(n) individual / gene pool:
Remember the Wobble of the
code in Silent Mutations?
This redundancy adds some
protection to our DNA!
– Beneficial (good)
• The natural environment can favor certain
changes in allelic frequencies.
• natural selection!!
– Harmful (bad)
– Neutral (neither good or bad)
Mutation: Radiation
• Radiation alters genes through
mutation and can turn on
oncogenes (genes promoting
cancer)
– UV Radiation from repeated,
overexposure to the sun.
– X-Ray Radiation from repeated,
overexposure to radioactive materials
& machines.
– Electromagnetic Radiation from
repeated, overexposure to high
frequency machines.
– Mutagens from toxic substances
(carcinogens) such as smog, pollution
and other man-made substances.
Example: Lead Poisoning
• Heavy metals are known
mutagens for genes.
• Many are poisoned by
their home environment
(old houses contain lead
paint)
• Modifies ALAD gene (on
Chromosome 3) which
alters hemoglobin
protein synthesis
– What symptoms would
manifest from this change
in protein synthesis?
Mutation: Viruses
• Viruses can live in the
body for long periods of
time up to an organism’s
entire lifetime.
• Some viruses have been
linked to changes in the
DNA causing diseases
and disorders:
– Example: Epstein Barr virus
has been linked to certain
types of cancer.
• Viruses are non-living particles
of nucleic acid, protein and
some lipids that cause
influenza.
• Composed of DNA or RNA in a
protein coat called a capsid.
• Named after their disease or
discoverer.
– Example: Viruses that only infect
bacteria are called
bacteriophages.
• Likely evolved later since they
are dependent on living
things.
• They cause changes in the
DNA of living things by the
methods in which they
replicate themselves…
What is a
Virus?
Viral “Reproduction”: Hiding
• Lysogenic cycle
– Virus attaches to host cell
– Inserts viral nucleic acid and
inserts it into the host
cell’s chromosome
(prophage)
– Gets replicated as host cell
divides (through mitosis)
– Can remain inactive for a
long period of time.
Like Bacteria, Viruses produce disease by disrupting the body’s normal
equilibrium. They either directly attack cells or cause cells to change their
patterns of growth or influence their function in the body.
Viral “Reproduction”: Attacking
• Lytic cycle
– Starts as the lysogenic
cycle until triggered.
– Takes over cell
machinery to make
virus only! (Chops up
cell’s DNA to shut
down all defenses.)
– Viruses are assembled
in the host cell
– Burst out of the host
cell releasing new
virus
• 30 min = 200 viruses
HIV virus
• Retroviruses
– Use RNA instead of DNA
– Reverse transcriptase
creates DNA from the RNA in
the host cell
• In Sub-Saharan Africa over
23 million living with
HIV/AIDS, 4 million
infected each year.
• HIV contact via
– Saliva/Sexual Contact
– Mucus Membranes
– Shared hypodermic
needles
– Blood transfusion (rare)
Remember
Viruses are Not Living!
• But wait, I thought containing DNA is a
component of all living things!
– Like the strawberry DNA!
• However, Viruses do not have these
components of living things…
– Are not made of cells (mostly protein and DNA)
– Cannot reproduce without a host cell.
• You cannot have one virus to make another virus (Mitosis)
• You cannot have a “male” and “female” virus to make new virus (Meiosis)
– Do not grow and develop.
• “Baby” viruses don’t grow up to become “adult” viruses.
So, is Mutation a good or a bad thing?
Changes in
DNA does
foster Genetic
Diversity in a
changing
environment!
How might
these
mutations be
beneficial for
these aliens
depending on
what type of
planet they
evolved on?