BIOL3150 Lecture Notes - Missense Mutation, Replica Plating, Silent Mutation
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Part B
Think about the DNA coding sequence of a gene. If an A were swapped for a T, what kind of mutation could it cause and why?
a) It could cause a frameshift nonsense or frameshift missense mutation because it would change the reading frame of the codon triplet. | ||||||||||||||||||||||||||||
b) It could cause a silent, missense, or nonsense mutation because those are the types that can be caused by a nucleotide-pair substitution like this one. | ||||||||||||||||||||||||||||
c) It could cause a nonsense mutation because the sequence would no longer be the same, so the protein would be shorter and non-functional. | ||||||||||||||||||||||||||||
d) It could cause a silent mutation because A and T are complementary to each other so it is not really a substitution mutation. Part C Why is a frameshift missense mutation more likely to have a severe effect on phenotype than a nucleotide-pair substitution missense mutation in the same protein?
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1.) Choose the best response for each.
a.) The Ames test is commonly used to test whether a particular chemical is mutagenic. When you conduct an Ames test, you need two groups of plates. One group of plates contains bacteria that are exposed to the chemical of interest, while the other plates contain bacteria that are not exposed to the chemical. Why is the latter group needed if you are just interested in the rate of mutation caused by the chemical?
The group without the chemical can be exposed to mammalian liver extract to see the effects of liver enzymes on the bacteria. |
Having two groups allows researchers to compare the effects of different environments on the mutation rate |
It is important to compare the rate of mutations with the chemical to the normal background mutation rate. Mutations occur spontaneously even without the presence of a mutagen. |
The second group is used as a control to make sure that the replica plating technique is done correctly. |
b.) Frameshift mutations can be very severe. What is one reason why they are often so serious?
When a frameshift mutation occurs, it causes transition mutations to occur. These are particularly severe. |
When a frameshift mutation occurs, it causes changes in many bases downstream and can affect many of the amino acids in the protein. |
Frameshift mutations always occur in the regulatory region, so they cause a gene to be turned off and then the protein is not produced at all. |
When a frameshift mutation occurs, it causes changes in many bases upstream and can affect many of the amino acids in the protein. |
c.) An organism that cannot synthesize methionine is called __________.
a mutant |
a prototroph |
an auxotroph |
an autotroph |