An enzyme is 320 amino acids long. Its active site includes amino acid 45. Table 1 shows four mRNA codons and the charge on the R group of each amino acid.
| mRNA codon | Amino acid | Charge on R group |
|---|---|---|
| GAA | glutamate | negative |
| GAG | glutamate | negative |
| AAA | lysine | positive |
| GGU | glycine | no charge (non-polar) |
A base substitution changes the codon for amino acid 45 from GAA to GAG. Use Table 1 to deduce the effect of this substitution on the enzyme.
[1]
A different substitution changes the codon for amino acid 45 from GAA to AAA. The enzyme's activity falls to zero. Use Table 1 to explain why.
[3]
A third substitution changes amino acid 210 from glycine to a different amino acid, but the enzyme's activity does not change. Suggest why.
[2]