Paper 2 · Proteins and Amino Acids
An adult haemoglobin molecule is made up of
Atwo alpha chains of 146 amino acids and two beta chains of 141 amino acids
Bfour identical alpha chains of 141 amino acids joined end to end by peptide bonds
Cfour identical beta chains of 146 amino acids joined to each other by disulphide bridges
Dtwo alpha chains of 141 amino acids and two beta chains of 146 amino acids
Explanation: Adult haemoglobin is a tetramer of two kinds of chain: two alpha chains of 141 amino acid residues and two beta chains of 146. The four chains are not identical, and they are held side by side rather than joined into one long chain.
Derived from ZIMSEC Biology Paper 2, Nov 2004, Q1