Question

You are a bioengineer and ask your student intern to reverse-engineer all possible mRNA sequences for a synthetic gene that can be used to express the peptide with the amino acid sequence Met-Lys-His in bacterial cells. The student brings you three possible sequences, but you know there should be four possible sequences. What would be the fourth sequence. 1. AUGAAACAU 2. AUGAAGCAU 3. AUGAAGCAC 4. ???

Answer 1

Peptide amino acid sequence is Met-Lys-His. Amino acids are coded by codon pressent on mRNA sequence. Each codon is made up of three nucleotides. There are several codon which code for same amino acid. Methionine (Met) which is also a start codon is coded by only single codon that is AUG. Lysine (Lys) amino acid is codedd by two codons which are AAA and AAG. Similarly Histidine (His) is coded by two codons which are CAU and CAC.  There are total four possible combinations of these codon which on translation can produce peptide Met-Lys-His.

these combinations are

AUGAAACAU

AUGAAACAC

AUGAAGCAU

AUGAAGCAC

So the combination which is missing is AUGAAACAC