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BIOL 2040 Lecture Notes - Lecture 12: Pyrimidine Dimer, Frameshift Mutation, Dna Replication

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School
York University
Department
Biology
Course
BIOL 2040
Professor
Tamara Kelly

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Document Summary

Visible mutation: most easily observed mutations are those affective a morphological trait. Are recognized by their ability to alter a normal or wild-type visible phenotype: regulatory mutation: affect the regulation of gene expression, can disrupt normal regulatory processes and inappropriately activate or inactivate expression of a gene. Lethal mutation: a mutation may adversely affect a gene product that is essential to the survival of the organism: conditional mutation: mutations exerts effects on the organism that depend on the environment in which the organism finds itself. Thus, during gamete production, the egg cells will bear the same sex chromosome, which is the x-chromosome: hetero, spontaneous vs. induced mutations, spontaneous: are changes in the nucleotide sequence of genes that appear to occur naturally. Tautomeric shifts: purines and pyrimidines can alternate chemical forms that differ by only a single proton shift in the molecule tautomeric forms. These shifts allow hydrogen bonding with non-complementary bases.

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Related Questions

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?

a) A substitution missense mutation causes the protein to be shorter and thus non-functional.
b) A frameshift missense will cause the codons to be out of order, but a substitution missense does not change the order of the codons.
c) A frameshift missense mutation will cause an early Stop codon, but a substitution missense might be silent.

d) A substitution missense affects only one codon, but a frameshift missense affects all codons downstream of the frameshift.

Part D

Which of the following sequences shows a frameshift mutation compared to the wild-type mRNA sequence?

a) wild-type 5’-AUGCAUACAUUGGAGUGA-3’
mutant 5’-AUGCAUACAGAGUGA-3’
b) wild-type 5’-AUGCAUACAUUGGAGUGA-3’
mutant 5’-AUGCAUACGUUGGAGUGA-3’
c) wild-type 5’-AUGCAUACAUUGGAGUGA-3’
mutant 5’-AUGCAUACAUCUGGAGUGA-3’
d) wild-type 5’-AUGCAUACAUUGGAGUGA-3’
mutant 5’-AUGCAUGUGACAUUGGAGUGA-3’

Part F

Suppose that the triplet of nucleotides indicated in bold (AGC) spans two codons, that is, CTA and GCC. If the triplet AGC were deleted from this DNA coding sequence, what effect would it have on the resulting protein?

5’-ATGCTAGCCTATCGTAAC-3’

a) The two flanking codons would be altered, but the rest of the amino acid sequence would be the same because there would be no frameshift.
b) The entire amino acid sequence would be altered due to the frameshift.
c) All of the amino acids after the deletion would be altered due to the frameshift.
d) All of the amino acids up to the deletion would be altered due to the frameshift.

A. What is the name of the main enzyme that performs transcription?

B. What is a mutation?

C. Why is the genetic code said to be degenerate?

D. How can a single base mutation (a change in a single nucleotide or base) result in a silent mutation, i.e. that does not result in a change in the amino acid sequence?

E. How can a change in a DNA nucleotide lead to a change in the protein?

F. How can knowing the 3D structure of a protein help scientists design effective drugs?

The amino-acid sequence shown in the following table was obtained from the central region of a particular polypeptide chain in the wild-type and several mutant bacterial strains: Codon 1 2 3 4 5 6 7 8 9

a. Wild-type: Phe Leu Pro Thr Val Thr Thr Arg Trp

b. Mutant 1: Phe Leu His His Gly Asp Asp Thr Val

c. Mutant 2: Phe Leu Pro Thr Met Thr Thr Arg Trp

d. Mutant 3: Phe Leu Pro Thr Val Thr Thr Arg

e. Mutant 4: Phe Pro Pro Arg

f. Mutant 5: Phe Leu Pro Ser Val Thr Thr Arg Trp

Each mutant represents a single nucleotide change from the original wild-type gene. For each mutant, explain what SINGLE nucleotide mutation at the DNA level accounts for the change(s) in amino acid sequence. Also, state in which codon and which position the mutation took place and then fully characterize the mutation as a base-pair substitution mutation (transversion or transition; and missense, nonsense, etc.) or a frameshift mutation. Finally, recreate as much of the original wild-type mRNA sequence as possible.