Amino acids and protein structureAQA A-Level Biology: Mind map

Exam questions on Amino acids and protein structure

1. Alanine is an amino acid whose R group is a methyl group, CH₃. Cysteine is an amino acid whose R group is CH₂SH, which contains sulfur.
   Explain why two cysteine molecules in a polypeptide can form a bond between their R groups that two alanine molecules cannot.2 marks
2. Haemoglobin is a protein made from four polypeptide chains: two α chains of 141 amino acids each and two β chains of 146 amino acids each.
   Explain why a change in the sequence of amino acids in a protein can change its function.2 marks
3. Ribonuclease is an enzyme made from a single polypeptide of 124 amino acids, folded into a compact three-dimensional shape. Its tertiary structure is held together by hydrogen bonds, ionic bonds and four disulfide bridges.
   Describe the primary, secondary and tertiary structure of ribonuclease.3 marks