(Choices A and C) Changing CUU (leucine) to AUU (isoleucine) or UAC (tyrosine) to CAC (histidine) would result in an amino acid substitution at one position (missense mutation). The function of this protein may be altered depending on a variety of factors, but the ultimate size of the protein will remain the same. Missense mutations that result in the substitution of a new amino acid with similar chemical properties are called conservative mutations.
(Choice B) Changing UAA to UAG would not affect protein structure or function because both of these sequences are stop codons. Stop codons are normally located at the end of the translated region of mRNA.
(Choice E) Changing UUU to UUC would not affect the protein as both sequences code for phenylalanine. Point mutations that do not change the amino acid sequence of a protein are called silent mutations.