Question

a chemical mutagen causes a point mutation in a dna molecule that changes the nucleotide adenine into guanine, as shown.

what effect will such mutation have on the function of the dna?

o the dna will code for the same protein.
o the dna will code for a nonfunctional protein.
o the dna will code for an incomplete protein.
o the dna will code for the same protein but of a different shape.

Explanation:

A point mutation changes one nucleotide in DNA. Here, adenine is changed to guanine. Looking at the normal and mutated DNA - mRNA - polypeptide sequences, we check if the amino acid sequence changes. In the normal DNA (5' - AUG UGC GAU AGC UUC CUA CUC - 3'), the mRNA codons code for specific amino acids (Met - Cys - Asp - Ser - Phe - Leu - Leu). In the mutated DNA (5' - AUG UGC GGU AGC UUC CUA CUC - 3'), the third codon changes from GAU (Asp) to GGU (Gly). Since the amino acid sequence changes (Asp to Gly), the protein will be non - functional as protein function is highly dependent on its amino acid sequence (primary structure which determines higher - order structures like secondary, tertiary, and quaternary). A change in a single amino acid can disrupt protein folding and its ability to perform its biological function.

Answer:

The DNA will code for a nonfunctional protein.