Question 4

Codon CUC to CUG represents a silent mutation.

A silent mutation occurs when a change in the nucleotide sequence does not alter the amino acid that is produced. The codon change from CUC to CUG both encode for the amino acid leucine, thus classifying it as a silent mutation.

A) GAA to GGU

This change results in a different amino acid being produced; GAA encodes for glutamic acid while GGU encodes for glycine. Therefore, this represents a missense mutation, not a silent mutation.

B) AGA to AGU

This codon change alters the amino acid produced; AGA encodes for arginine and AGU encodes for serine. This represents a missense mutation, as the change results in the substitution of one amino acid for another.

C) CUC to CUG

Both CUC and CUG codons encode for the same amino acid, leucine. This change does not affect the protein's primary structure, making it a silent mutation.

D) UUA to UUU

This change results in the production of different amino acids; UUA encodes for leucine while UUU encodes for phenylalanine. This represents a missense mutation, which alters the resulting protein.

Conclusion

The change from CUC to CUG is definitively a silent mutation because it does not alter the amino acid sequence of the resulting protein. In contrast, all other options result in changes to the amino acid sequence, classifying them as missense mutations. Thus, C is the only correct answer reflecting a silent mutation.