Question

Benzene, a known carcinogen, mutates a sequence of dna in a gene. the previous sequence contained tac ggc acg ttt att, and the mutation caused the seventh nucleotide (with an adenine base) to be replaced by a nucleotide with a cytosine base. how will the final mutated polypeptide be different from the original polypeptide?

Answer 1

This would change the type of amino acid in the third position of the polypeptide chain. ACG codon codes for Threonine while CCG codes for Proline. This mutation will change the conformation of the protein especially because threonine is a polar amino acid (hydrophilic) while proline is hydrophobic

Answer 2

Mutations are changes in the orders of the nucleotides in the DNA. It could be done by physical or chemical factors, like UV, Benzene, or chemotherapy agents.

Let's take a look at the DNA sample:
tac ggc acg ttt att
the seventh nucleotide will be replaced by cytosine.
tac ggc ccg ttt att

So this change will affect the resulting polypeptide. the amino acid which is coded by ACG will be changed by the amino acid coded by CCG.

ACG code for threonine, and CCG code for proline.

Threonine and proline are different in structure and property so it could affect the protein, especially if the amino acid is located in the active site.
It should be known that the majority of mutation in the first nucleotide of the codon will cause changes in the resulting protein.