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TAKS Objective 2
TEKS 6C (Mutations)
Presented by:
Alexander Fedorov
Composite Science Teacher
TAKS Objective 2
TEKS 6C (Mutations)
6C The student knows the structures
and functions of nucleic acids in the
mechanisms of genetics. Students
should be able to identify and
illustrate how changes in DNA
cause mutations and evaluate
the significance of these
changes.
Wild Type Head
Mutant Head (Antennapedia)
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Proteins and Mutations:
Some proteins carry out
functions within the cells of an
organism.
Other proteins are exported
out of the cell for other
purposes.
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Still other proteins are used as
activators or repressors, turning
genes on or off.
Therefore, a change in a cell’s
proteins could have dramatic effects
on the cell’s structure or function.
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Changes in the DNA can change the
proteins made by the cell.
A random change in the sequence of
nucleotides in DNA is called a mutation.
Some mutations have little or no
effect on the organism, others
are harmful and very few are
beneficial.
Harmful
mutations,
Ahhhhh!!!
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There are two types of mutations:
1. Chromosomal mutations
2. Gene mutations
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Chromosomal mutations are changes
in the structure of a chromosome.
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Gene mutations are errors that occur
within individual genes in a
chromosome.
Gene mutations can involve a single
nucleotide or they can affect sections
of DNA that include many
nucleotides.
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The deletion or
addition of
nucleotides that
disrupts codons is
called a
frameshift
mutation.
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Because mRNA is read in codons
(three-base sections) during
translation, an addition or deletion of
nucleotides can alter the sequence of
bases, or reading frame, of the
genetic message.
What are the codons in the original reading frame?
What are the codons in the shifted reading frame?
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Recall what happens when a strand
of mRNA is transcribed from DNA.
What might happen if one base is
deleted from the DNA?
The transcribed mRNA would also be
affected.
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Because each mRNA codon
corresponds to an amino acid,
altering the codons may alter the
amino acid sequence.
The end result may be an entirely
different protein product. Frameshift
mutations can have an enormous
impact on an organism’s structure
and function.
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A change in only one
nucleotide is a
point mutation.
Because a point
mutation affects a
single codon, it tends
to be far less
disruptive than a
frameshift mutation
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Some amino acids are coded for by more
than one codon, and substitution may
simply change one codon to another
codon for the same amino acid.
For example:
CUU = Leucine
Any change in the third base: CUC, CUA,
CUG
still codes for the amino acid Leucine.
Third Letter
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About 30% of all substitution
mutations produce no changes in
proteins.
In the remaining 70% of point
mutations, changed nucleotides cause
a different amino acid to be
incorporated into a protein.
The resulting protein may function
normally or may be defective
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The diagram shows
a point mutation
and how it changes
the gene from
normal hemoglobin
production to the
production of
sickle-cell
hemoglobin, which
in turn causes
sickle-cell disease.
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A third and very common point mutation
occurs when a codon in the middle of a
gene is changed to a stop codon.
For example: UGC = Cysteine but UGA =
Stop
When genes with this mutation go through
protein synthesis, translation is halted
before the amino acid chain is completed.
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Here is a sampling of
the more than 200
different mutations
that have been found
in patients with cystic
fibrosis
Unlike sickle-cell disease,
then, no single mutation is
responsible for all cases of
cystic fibrosis. People with
cystic fibrosis inherit two
mutant genes, but the
mutations need not be the
same.
1 Ultraviolet radiation can cause mutations
in the DNA of skin cells that have been
overexposed to the sun. This mutated
DNA has no effect on future offspring
because —
A changes in skin cell DNA are
homozygous recessive
B mutations must occur within the RNA
codons
C offspring reject parental skin cells
D only changes to gamete DNA can be
inherited
1 Ultraviolet radiation can cause mutations
in the DNA of skin cells that have been
overexposed to the sun. This mutated
DNA has no effect on future offspring
because —
A changes in skin cell DNA are
homozygous recessive
B mutations must occur within the RNA
codons
C offspring reject parental skin cells
D only changes to gamete DNA can be
inherited
2 Mutations in DNA molecules can
occur when —
A replication of DNA is exact
B a DNA enzyme attaches to an RNA
codon
C RNA codons are replaced by DNA
nucleotides
D a change occurs in DNA nucleotide
bases
2 Mutations in DNA molecules can
occur when —
A replication of DNA is exact
B a DNA enzyme attaches to an RNA
codon
C RNA codons are replaced by DNA
nucleotides
D a change occurs in DNA nucleotide
bases
AGAUCGAGUACAUCGAGU
3 The chain above represents three codons. Which of the
following changes would be expected in the amino acid chain
if the mutation shown above occurred?
A The amino acid sequence would be shorter than expected.
B The identity of one amino acid would change.
C The amino acid sequence would remain unchanged.
D The identities of more than one amino acid would change.
AGAUCGAGUACAUCGAGU
3 The chain above represents three codons. Which of the
following changes would be expected in the amino acid chain
if the mutation shown above occurred?
A The amino acid sequence would be shorter than expected.
B The identity of one amino acid would change.
C The amino acid sequence would remain unchanged.
D The identities of more than one amino acid would change.
4 The diagram represents the chromosomes of a person
with a genetic disorder caused by nondisjunction, in which the
chromosomes fail to separate properly. Which chromosome set
displays nondisjunction?
A2
B8
C 21
D 23
4 The diagram represents the chromosomes of a person
with a genetic disorder caused by nondisjunction, in which the
chromosomes fail to separate properly. Which chromosome set
displays nondisjunction?
A2
B8
C 21
D 23
5 The assembly of a messenger RNA strand that normally begins
with UAC has been changed so that the newly assembled
messenger RNA strand begins with UAG. Which of the following
will most likely occur?
A The protein will be missing the first amino acid.
B The amino acids that make up the protein will all be different.
C The mRNA will become attached to a ribosome.
D The production of the protein will be stopped.
5 The assembly of a messenger RNA strand that normally begins
with UAC has been changed so that the newly assembled
messenger RNA strand begins with UAG. Which of the following
will most likely occur?
A The protein will be missing the first amino acid.
B The amino acids that make up the protein will all be different.
C The mRNA will become attached to a ribosome.
D The production of the protein will be stopped.
The End