Base triplet Amino acid GCA alanine AAT asparagine CTG leucine TAC tyrosine GGT glycine A short length of a gene carries the coded instructions for making p...

This question tests the genetic code: how the order of bases in a gene fixes the order of amino acids in a protein. Reading the code from Table 1.1 gives the answers directly.

(a) A group of three bases that codes for one amino acid is a base triplet (codon). [1]

(b) Reading each triplet from the table: GCA gives alanine, AAT gives asparagine, CTG gives leucine, so the order is alanine - asparagine - leucine. [2, 1 per two correct]

(c) Amino acids are assembled into proteins at the ribosomes (in the cytoplasm). [1]

(d) The base sequence determines the structure of the hormone as follows [4]: the order of bases forms a code [1]; each triplet of three bases codes for one particular amino acid [1]; this fixes the exact order in which the amino acids are joined together [1]; and that sequence of amino acids gives the hormone its particular structure and shape [1]. [4]

(e) The hormone has the same amino acid sequence every time because the gene has the same fixed base sequence each time it is used [1], so the same triplets code for the same amino acids in the same order [1]. [2]

(f) The sequence may differ slightly between two people because a mutation (a change in the base sequence of the gene) [1] can change one or more of the amino acids in the chain [1]. [2]

(g) One other use of proteins: as enzymes (also accept structural proteins, antibodies, or haemoglobin). [1]