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Question

Structural diagram: amino acid with R group: CH₃

a mutation in the gene coding for a single-polypeptide enzyme results in the substitution of the amino acid serine, which has a polar R group, by the amino acid phenylalanine, which has a non polar R group. When researchers test the catalysis of the normal enzyme and the mutated enzyme, they find that the mutated enzyme has much lower activity than the normal enzyme does. Explain how the amino acid substitution might have resulted in decreased activity by the mutated protein.

Answer 1

In the given question, the mutation of the gene causes the substitution of serine by phenylalanine amino acid, which causes a decrease in the activity of the enzyme. Serine is polar, hence it will be involved in the formation of bonds with the substrate. Hence, the substitution changed the enzyme's secondary and tertiary structures, causing the mutant enzyme to fold in a different way than the normal enzyme.