4.) Explain the difference between the following point mutations: Silent Missens

Question

4.) Explain the difference between the following point mutations:

Silent

Missense

Nonsense

5.) Explain the difference between a conditional lethal mutation, suppressor mutation and back mutation.

6.) Explain the difference between somatic and germ line mutations. Which type can be passed on to progeny?

7.) Which of the following amino acid substitutions should you expect to be induced by 5-bromouracil with the highest frequency? (a) Met —> Leu; (b) Met —> Thr; (c) Lys —> Thr; (d) Lys —> Gln; (e) Pro —> Arg; or (f) Pro —> Gln? Why?

Explanation / Answer

Silent Mutation:

These mutations do not change the amino caud sequence of polypeptides thereby do not alter phenotype of organism in which they occur.

For example; Nucleotide sequence CAGCAGCAGCAG in DNA will be transcribed in codons GUCGUCGUCGUC, which will translate into amino acid sequence Val-Val-Val-Val. Substitution of nucleotide G at the third position with A will change DNA sequence into CAACAGCAGCAG that will be transcribed into codons GUUGUCGUCGUC. this codon (GUU) will still code for the same amino acid, valine. So amino acid sequence in polypeptide will be same.

Val-Val-Val-Val

Missense mutation:

It is a type of point mutation, in which there occurs a single nucleotide change in DNA. This single nucleotide change results in transcription of codon that codes for a different amino acid.

For example; Nucleotide sequence CAGCAGCAGCAG in DNA will be transcribed in codons GUCGUCGUCGUC, which will translate into amino acid sequence Val-Val-Val-Val.

Due to substitution of nucleotide A at the 5th position with C, second codon GUC will change into codon GGC that codes for amino acid Glycine.

Amino acid sequence will therefore be Val-Gly-Val-Val.

Nonsense mutation:

A.mutation in which a sense codon that corresponds to one of the twenty amino acids specified by the genetic code is changed to a chain-terminating codon.

For example; codon UAU codes for amino acid tyrosine. Due to substitution of U at the third position by A, codon UAU is changed into codon UAA that is a stop codon and causes termination of synthesis of polypeptide chain.

Related Questions

Navigate

• Browse (All)
• Browse 4
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.