The amino acid sequences below come from the middle of a protein. Several differ
ID: 68652 • Letter: T
Question
The amino acid sequences below come from the middle of a protein. Several different mutants have been identified with changes in this protein.
Codon
1
2
3
4
5
6
7
8
9
Wild type
Phe
Leu
Pro
Thr
Val
Thr
Thr
Arg
Trp
Mutant 1
Phe
Leu
His
His
Gly
Asp
Asp
Thr
Val
Mutant 2
Phe
Leu
Pro
Thr
Met
Thr
Thr
Arg
Trp
Mutant 3
Phe
Leu
Pro
Thr
Val
Thr
Thr
Arg
1) For each of the mutants (1-3), state what the effect of the mutation will be at the polypeptide level (frameshift, missense etc), and in which codon the mutation occurred. Use the genetic code to help you.
2) For each mutant, state what exact change has occurred at the DNA level (what nucleotide has been added, substituted, etc). Specify the exact nucleotide change.
3) If these changes happened during the translation of a the protein, and didn’t affect the DNA sequence of the gene, would this change how much they might affect the phenotype of an organism? Explain your answer.
4) Why do insertions and deletions often have more drastic phenotypic effects than do base substitutions?
Codon
1
2
3
4
5
6
7
8
9
Wild type
Phe
Leu
Pro
Thr
Val
Thr
Thr
Arg
Trp
Mutant 1
Phe
Leu
His
His
Gly
Asp
Asp
Thr
Val
Mutant 2
Phe
Leu
Pro
Thr
Met
Thr
Thr
Arg
Trp
Mutant 3
Phe
Leu
Pro
Thr
Val
Thr
Thr
Arg
Explanation / Answer
4) nsertions and deletions can results in frame shifts which would cause every codon to code for a different protein, drastically changing the original phenotype. However, base substitutions only affect one codon
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