Describe how one amino acid is added to a polypeptide that is being formed at a ribosome during translation.

Crystallin is a structural protein found in the human eye. An inherited disease that leads to blindness is caused by changes in properties of crystallin. The replacement of the amino acid Arg with the amino acid Gly causes these changes.

Use information in Table 2 to suggest why this amino acid replacement changes the properties of crystallin.

The amino acid replacement of Arg with Gly is caused by a single base substitution mutation in the DNA. The non-mutant DNA triplet is TCC.

Complete Table 3.

Give:

• the mRNA codon complementary to the non-mutant DNA triplet • the mutated mRNA codon that could cause the change from Arg to Gly in the crystallin protein • the DNA triplet complementary to this mutated mRNA codon.

mRNA codon for the non-mutant triplet

Mutated mRNA codon

Mutated DNA triplet