Answer to Question #161568 in Molecular Biology for Virat

Question #161568

Task 1. When nitrous acid acts on DNA molecules, cytosine is replaced by guanine. Determine the type of mutation. Explain the mechanism. What structure will a section of the synthesized protein have if a polypeptide with the following amino acid sequence was to be formed: ser - ile - tre - proser, but all cytosine nucleotides of the corresponding DNA region underwent the specified chemical transformation? Determine the type of mutation.








1
Expert's answer
2021-02-08T10:26:55-0500

Nitrous acid reacts with bases that contain amino groups leading to deamination. Adenine is oxidatively deaminated to hypoxanthine, cytosine to uracil, and guanine to xanthine. As a result, nitrous acid leads to the substitution of one base pair for another causing mismatch pairing. The replacement of cytosine to guanine is a transversion mutation (the replacement of a pyrimidine by a purine).

As ser is encoded by the codon UCA, the mutation will lead to the formation of stop codon UGA. As a result, the polypeptide will not be synthesized and the protein will lack the required structure. The type of mutation is called a nonsense mutation.


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