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Biology 1002B Lecture Notes - Lecture 18: Silent Mutation, Reading Frame, Codeine

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Western University
Department
Biology
Course
Biology 1002B
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Document Summary

Missense mutation: a snp (single base pair change) might change a codon which might result in a different amino acid, silent mutations: change in dna that leads to no change in the phenotype. Frameshift mutation: base pairs are read in increments of 3 bases, if a base is deleted, the reading frame shifts and the whole phenotype is changed as all codons downstream are changed. Resulting protein will be either long or short. Splicing will not be affected by the base insertion. Short: reading frame shorts and creates bases at the end that can"t be read and then wont be able to add a protein. A stop codeine might be added in the middle of the gene and the protein might end up being too short. Long: if frame is shifted, the stop coding might not be in the frame and then translation would not stop at the usual spot making the gene longer than it is supposed to be.

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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.

The effect of base-pair substitution mutations on protein function varies widely from no detectable effect to the complete loss of protein function (null allele).

Part A Why do the functional consequences of base-pair substitution vary so widely? Select the four correct answers.

1. Nucleotide substitutions might not cause changes in the amino acid sequence of the protein.

2. The reading frame of the gene could be affected by base-pair substitution mutations, which almost always leads to lack of function.

3. Nucleotide substitutions in exons always lead to changes of amino acids in the protein.

4. The reading frame of the gene could be affected by base-pair substitution mutations, which rarely leads to lack of function.

5. Missense mutations create amino acid substitutions, which might affect protein functionality.

6. Mutations that occur in the intron sequences generally do not affect protein functionality.

Predict which type of mutation is most likely to result in adisasterous change in a protein?

a) Substitution that does nto change the protein sequence

b) Missense mutation that changes protein sequence by onenucelotide

c) One nucleotide insertion that causes frame shift

d) Three nucleotide deltion that oes not change the readingframe