Assume that the following is the entire sequence of a short protein which did no

Question

Assume that the following is the entire sequence of a short protein which did not require mRNA splicing prior to its translation: NH2-Met-His-Leu- Tyr-Ile-His-Cys-Trp-Gln-Lys-Phe-COOH

a. Write out the sequence of a possible mRNA molecule encoding this protein. You do not need to write out 5’-UTR or 3’-UTR sequences. Be sure to label 5’ / 3’ directionality.

b. Write out the sequences of both strands of the double-stranded DNA molecule corresponding to the mRNA and protein. You only need to write the portion of the double-stranded DNA molecule which corresponds to the mRNA sequence in part (a). Label the template and non-template strands as well as 5’ / 3’ directionality.

c. Identify three bases in the DNA molecule, each of which, if mutated, will result in a nonsense mutation. Above each of these nucleotides, write the base which will result in a nonsense mutation.

Explanation / Answer

1. a. The sequence of a possible mRNA molecule encoding the given protein NH2-Met-His-Leu- Tyr-Ile-His-Cys-Trp-Gln-Lys-Phe-COOH is,

5'- AUG CAU UUG UAU AUA CAU UGU UGG CAG AAA UUU - 3'

The 5' end corresponds to amino acid end and the 3' end corresponds to carboxylic acid end.

b. The strand of double stranded DNA are,

5'- ATG CAT TTG TAT ATA CAT TGT TGG CAG AAA TTT - 3' ----------> Coding strand

3- TAC GTA AAC ATA TAT GTA ACA ACC GTC TTT AAA -5' ------------> Template strand

c. The coding strand sequence is, 5'- ATG CAT TTG TAT ATA CAT TGT TGG CAG AAA TTT - 3', in which replacement of cytosine with thymine (T) turns it into a stop codon (nonsense mutation).

5'- ATG CAT TTG TAT ATA CAT TGT TGG TAG AAA TTT - 3' -----------> Nonsense mutation.

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