Question

Genetic code: 1. How many silent mutations can be made starting from the codon TGG? (2 points) A. O B. 1 C. 2 D. 3 Answer: 2. How many single base changes result in nonsense mutations for the codon TCA? (2 points) A. O B. 1 C. 2 D. 3 E. 4 Answer: 3. How many single base change missense mutations are possible for codon ATG resulting in how many different amino acids? (2 points) A. 3,3 B. 5, 3 C. 7,4 D. 8,5 E. 9,6 Answer:

Answer 1

1. Silent mutation - In this type of mutation, substitutions of nucleotide bases do not change the amino acids coded from the codon.

TGG codon codes for tryptophan protein. Tryptophan is coded only from TGG codon. That's why any base substitution in TGG codon will change the translated protein.

Hence, the option 'A' is the correct one, i.e., no silent mutation can be made starting from the codon TGG.

2. Nonsense mutation - In this type of mutation a sense codon will be mutated to one of the chain-terminating codons. There are three chain-terminating codons. They are TAA, TAG, TGA. TAA is called ochre, TAG is called amber, TGA is called opal.

Mutation from TCA to TAA and from TCA to TGA can be resulted by single base change. Mutation from TCA to TAG can not be resulted by single base change. Hence, the option 'C' is correct, i.e., two single base changes result in nonsense mutations for the codon TCA.

3. Missense mutation- In this type of mutation change of a nucleotide base change the amino acids coded from that codon.

Possible single base change missense mutations of the codon ATG and translated proteins from those codons are listed below.

1. TTG - Leucine

2. GTG - Valine

3. CTG - Leucine

4. AAG - Lysine

5. AGG - Arginine

6. ACG - Threonine

7. ATA- Isoleucine

8. ATT - Isoleucine

9. ATC - Isoleucine

ATG codes for methionine protein.

The number of possible single base change missense mutations of the codon ATG is 9 and the number of translated proteins from those codons is 6.

Hence, the option 'E' is the correct one.