Mutations
(Chapter 5.6)
What are Mutations?
 Errors in DNA
 They can be inherited if they occur in the sex cells
 Can be caused by mutagens or occur spontaneously
Effects of Mutations:
 Silent Mutation
 No effect on the cell
 A change in an intron
 A change in a base which results in the production of
the same amino acid (due to the redundant nature of
DNA)
 Missense Mutations
 Single substitution of one amino acid in a polypeptide
(sickle cell anemia)
 Nonsense Mutation
 Stop codon is substituted and as a result the
polypeptide is incomplete
Types of Mutations:
1. Point Mutations: the mutation occurs at a specific base
pair in the genome
 Frameshift mutations occur when the reading frame of
the codons is shifted – all amino acids after the mutation
will be altered.
This can be caused by an insertion (addition of a
base) or a deletion (removal of a base).
 Substitution mutations occur when one base is
replaced by a different base.
2. chromosomal mutations:
 Translocation – chromosomes swap chunks (usually
between non-homologous chromosomes which is why
they are mutations). Some types of leukemia are
associated with translocation mutations.
 Transposable genes (transposons) – chunks of DNA
that are always moving from one location to another
(disrupting the correct sequences of DNA) … once
called “jumping genes”
*1983: Barbara McClintock was awarded the Nobel Prize
for discovery of transposable elements in corn.
Aside: One class of transposable genes called retrotransposons behave very
similarly to retroviruses, such as HIV. This may provide a clue as to the
possible evolutionary origins of this virus and other related ones.
 Inversion – a section of DNA in reversed
*See pg. 260 – have a look at the summary pictures of
different types of mutations that can occur.
Causes of Mutations
Mutations can be induced by exposure to different things,
or they can occur spontaneously.
Spontaneous
Errors of this kind are simply caused by error of the genetic
machinery. DNA polymerase I rereads the duplicated DNA
to check for mistakes, but occasionally it misses them!!
This may result in point mutations.
Mutagenic Agents (mutagens)
 Exposure to things like UV radiation, cosmic rays, X
rays, and certain chemicals, including some pesticides
can induce mutation.
 The mutagens attack and damage the DNA in different
ways. Your cells will try to repair the DNA, but they are
not always successful.
 Mutations at certain sites within the genome may lead to
cancer. Mutated versions of genes that control the cell
cycle are referred to as oncogenes: these are the “cancer
causing” genes.
What is cancer?
 Interesting:
o Some chemicals acts as mutagens because they
resemble building blocks of the DNA (like evil
molecular twins) and may be incorporated into the
DNA.
o This capability has been used in AIDS therapy:
How? Some of the chemicals in AIDS drugs resemble
nitrogenous bases found in DNA. They insert
themselves into the viral DNA and then when it
comes time for the virus to copy, the DNA
polymerase stops because it does not recognize the
imposter nitrogenous base.
 Complete questions on pg. 263 AND make sure that you are
comfortable with all the summary points on the same page.
 Read section 5.7 and 5.8 on your own and make summary
notes.
 Make sure that you have read ALL of chapter 5 … and check
out pages 272-273 for summary and self quiz.
Mutations
(Chapter 5.6)
What are Mutations?
Effects of Mutations
 Silent Mutation

 A change in an intron

 Missense Mutations
 Single substitution of
 Nonsense Mutation
 Stop _______________________ and as a result the polypeptide is
incomplete
Types of Mutations
Point Mutations: the mutation occurs at a specific base pair in the genome
 Frameshift mutations occur when the ____________________ of the codons
is shifted – all amino acids after the mutation will be altered.
This can be caused by an insertion (________________) or a deletion
(_________________________________).
 Substitution mutations occur when __________________________ by a
different base.
Mutations at the chromosomal level:
 Translocation – chromosomes swap chunks
(_________________________________________________________________________
____). Some types of leukemia are associated with translocation mutations.
 Transposable genes (transposons) – chunks of DNA that are always
_________________________________________________ (disrupting the
correct sequences of DNA) … once called “jumping genes”
*1983: Barbara McClintock was awarded the Nobel Prize for discovery of
transposable elements in corn.
Aside: One class of transposable genes called retrotransposons behave very
similarly to retroviruses, such as HIV. This may provide a clue as to the
possible evolutionary origins of this virus and other related ones.
 Inversion –
*See pg. 260 – have a look at the summary pictures of different types of
mutations that can occur.
Causes of Mutations
Spontaneous
Errors of this kind are simply caused by error of the ____________________. DNA
polymerase I rereads the duplicated DNA to check for mistakes, but
occasionally it misses them!! This may result in _____________________________.
Mutagenic Agents (mutagens)




Exposure to things like _______________, cosmic rays, X rays, and certain
chemicals, including some ________________ can induce mutation.
The mutagens attack and damage the DNA in different ways. Your cells will
try to _____________________, but they are not always successful.
Mutations at certain sites within the genome may lead to cancer. Mutated
versions of genes that control the cell cycle are referred to as
____________________: these are the “cancer causing” genes.
What is cancer?
Interesting:
o
o This capability has been used in AIDS therapy: How? Some of the
chemicals in ___________________ resemble nitrogenous bases found in
DNA. They insert themselves into the ______________ and then when it
comes time for the virus to copy, the __________________________
because it does not recognize the imposter nitrogenous base.
 Complete questions on pg. 263 AND make sure that you are comfortable
with all the summary points on the same page.
 Read section 5.7 and 5.8 on your own and make summary notes.
 Make sure that you have read ALL of chapter 5 … and check out pages
272-273 for summary and self quiz.