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BIOL 039 Lecture Notes - Lecture 17: Trinucleotide Repeat Disorder, Tandem Repeat, High Fidelity

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pucemallard867
7 Jan 2021
School
Pasadena City College
Department
Biology
Course
BIOL 039
Professor
Lgoe

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Document Summary

Missense mutation: a base-pair change that alters a single amino acid for another one in the protein. Nonsense mutation: a base-pair change that creates a stop codon in place of a codon specifying an amino acid. Silent mutation: a base-pair change that does not alter the resulting amino acid sequence due to the redundancy of the genetic code. Forward mutation wild type to mutant type. Reverse mutation mutant type to wild type. Neutral mutation a single aa change (missense mutation) that does not alter protein activity/function. Base-pair substitutions can cause (a) missense, (b) nonsense, and (c) silent mutations. Effects of mutations (base-pair insertion and deletion mutations) Insertion or deletion of one or more base pairs in the coding sequence leads to addition or deletion of mrna nucleotides, altering the orf of the message. The wrong amino acid sequence and premature stop codons are produced downstream of the altered nucleotides. Forward mutation: converts a wild-type to a mutant phenotype.

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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 mutation has resulted in changes to both the size (number of amino acids) and the amino acid composition of the protein encoded by a gene. This mutation is most likely a (an) ---------.

A.

Deletion of the promoter
B.

Insertion or deletion of a base pair in an exon

C.

Single missense mutation in the transcription region
D.

A base substitution, which has changed the start codon to 5'ACG3'
E.

Insertion or deletion of a base in the middle of an intron

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.