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

Exam questions on Amino acids and protein structure

1. A biochemist mixes two amino acids, glycine and alanine, in solution and adds a catalyst that allows them to join together to form a dipeptide. Both amino acids have the same general structure, with an amino group, a carboxyl group, a hydrogen atom and an R group attached to a central carbon atom.
   Explain, in terms of the atoms lost from the two amino acids, why the formation of the dipeptide is a condensation reaction.2 marks
2. A globular protein from a bacterium is a single polypeptide chain. Its primary structure contains two cysteine amino acids that are far apart in the sequence. In the folded protein, the sulfur-containing R groups of these two cysteines lie close together. The interior of the protein is made mostly of amino acids with hydrophobic R groups.
   Explain how the primary structure of this protein determines its tertiary structure.2 marks
3. Haemoglobin is the protein in red blood cells that carries oxygen. A molecule of haemoglobin is made of four polypeptide chains, each folded into a compact shape and each containing a haem group with an iron(II) ion. Haemoglobin is dissolved in the cytoplasm of the red blood cell at a very high concentration. A single red blood cell contains about 2.7 × 10⁸ haemoglobin molecules.
   Explain why haemoglobin is a globular protein that is soluble in the cytoplasm of the red blood cell.3 marks