2. After cloning the Citrate Synthase gene you consulted the genome databases an

Question

2. After cloning the Citrate Synthase gene you consulted the genome databases and find that the human Citrate Synthase enzyme (found in the Krebs Cycle) primary conformation begins with the amino acid sequence Met-Trp-Lys-Trp- Trp-Met. But the protein made from your plasmid begins with Met-Trp-Met-Trp-Irp-Met! A mutation must have occurred! Write out the most likely DNA sequence of the non-templated strand for the beginning of the actual (unmutated) Citrate Synthase gene. Don't forget 5' and 3' ends. (10 Points)

Explanation / Answer

Amino acid sequence for mutated Citrate synthase is:

N-Met-Trp-Met-Trp-Trp-Met-C

mRNA is

5’ AUG UGG AUG UGG UGG AUG 3’

mRNA strand has the same sequence as non-template strand that runs in 5’ to 3’ direction

Non-template strand

5’ ATG TGG ATG TGG TGG ATG 3’

Lysine is substituted by methionine in the mutated protein. Lysine is coded by AAG or AAA, while methionine is coded by AUG. Hence, the codon for this lysine in the unmutated strand should be AAG as there is a substitution of A with U (or T in DNA).

Amino acid sequence for unmutated Citrate synthase is:

N-Met-Trp-Lys-Trp-Trp-Met-C

mRNA is

5’ AUG UGG AAG UGG UGG AUG 3’

Non-template strand

5’ ATG TGG AAG TGG TGG ATG 3’

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