Question

The sequence below represents the coding DNA strand of the start of a gene, including part of the 5' untranslated region.

(5')...TCGGAAGGAGGTAGCGGCAATGGGGAAAAGTATTGCTT...(3')

In studying variants of this gene in disease, a nucleotide mutation of A→T was detected in the first base of the third codon. What effect would this mutation have?

(When considering your answer, assume standard initiation of translation is numbered as codon 1.)

Select one:

a. Terminates translation

b. No effect

c. Disrupts ionic interactions at physiological pH

d. Disrupts disulphide bond formation

Answer 1

5'-TCGGAAGGAGGTAGCGGCAATGGGGAAAAGTATTGCTT-3'     DNA Coding Strand

3’-AGCCTTCCTCCATCGCCGTTACCCCTTTTCATAACGAA-5’       DNA Template Strand

5'-UCGGAAGGAGGUAGCGGCA-AUG-GGG-AAA-AGU-AUU-GCU-U-3'     mRNA Strand

                                                     N-Met-Gly-Lys-Ser-Ile-Ala-C                       Polypeptide

Upon nucleotide mutation of A→T in the first base of the third codon,

5'-TCGGAAGGAGGTAGCGGCAATGGGGTAAAGTATTGCTT-3'     DNA Coding Strand

3’-AGCCTTCCTCCATCGCCGTTACCCCATTTCATAACGAA-5’       DNA Template Strand

5'-UCGGAAGGAGGUAGCGGCA-AUG-GGG-UAA-AGU-AUU-GCU-U-3'     mRNA Strand

                                                     N-Met-Gly-STOP                                         Polypeptide

This mutation terminates translation prematurely, due change of AAA (Lys) to UAA (STOP codon).