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Mutations
Changes in DNA may result in disease
Mutations: Page 96
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1) Define mutation from page 224 in your
textbook.
2) Decide from paragraph 2 if all mutations
are bad. Write down on your left side page
what you determine
3) If there is a mutation, what can happen to
a protein?
Point Mutations: 3 Types
Substition, Insertion,
or deletion
of a nucleotide.
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Point Mutations: Substitution
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One N-base is substituted for
another.
The change in DNA results in
a different mRNA codon.
The different codon may
result in a different amino
acid.
A change in the amino acid
sequence of a protein will
likely change the protein’s
shape. (Remember-shape
determines function!)
Point Base Mutation:
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From the Insulin Lab Section #3
The first 9 DNA bases where:
TACAAACAT
Find the mRNA, then find the 3 amino acids
Now replace the first letter with another base.
Record what happens to the amino acids.
An Example of Substitution: Sickle cell
anemia
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A disease resulting from
an incorrect amino acid
in the hemoglobin
protein (the protein in
red blood cells that
carries oxygen).
The protein has the
wrong shape, so the
blood cells become
“sickled”, causing
numerous physiological
problems.
Another Type: Frame-shift mutations
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Results from either:
A. Insertion
A N-base is inserted
B. or deletion
A N-base is deleted.
Shifts the “reading-frame” of
mRNA codons.
All codons “downstream” are
affected.
Causes many amino acids
to be incorrect in the
protein.
Write out the same DNA sequence
:TACAAACAT
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1st: Insert one extra base at the beginning,
what happens?
Write down the resulting amino acids
2nd: Take out 3 bases from the beginning,
what happens?
Write down the resulting amino acids
What can point mutations cause?
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Sequence of the amino acid changes
Number of the amino acid changes
Type of amino acid changes
What does this cause to happen in the
protein?
Genetic disease and frameshift mutations
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Cystic fibrosis: deletion
of 3 bases results in a
protein that is missing
one amino acid.
Muscular dystrophy:
caused by
insertions/deletions in a
critical muscle protein.
Cancer is a disease that results from
mutations
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All types of cancer have one thing in
common; control of the cell cycle is defective.
Cell division goes “out of control” resulting in
tumors.
The cell cycle is regulated by proteins. If
these proteins are defective, cells divide
prolifically.
Developing cancer is a multi-step process
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It takes more than a single mutation for
cancer to develop. This helps explain a few
things:
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Older people are more likely to get cancer. The
longer someone lives, the more mutations
accumulate in their DNA.
Some people have a predisposition to get certain
types of cancer, such as breast cancer. If
someone inherits a mutation they need only get
one or two more to develop cancer.
Causes of mutations
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Errors in DNA replication.
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X-rays, UV light, and other types of radiation.
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DNA polymerase “proofreads” during replication
and catches most errors.
Sunscreen helps prevent melanoma, skin cancer.
Toxic chemicals
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Smokers are more likely to get lung and mouth
cancers, etc.