ProteinsAQA A-Level Chemistry: Mind map

Exam questions on Proteins

1. Glycine, H₂NCH₂COOH, and alanine, CH₃CH(NH₂)COOH, can join together to form dipeptides.
   Give the structural formula of the dipeptide in which the –COOH group of glycine has reacted with the –NH₂ group of alanine, and identify the peptide link.2 marks
2. A mixture of amino acids from the hydrolysis of a protein is separated by thin-layer chromatography (TLC). The plate is then sprayed with ninhydrin. The solvent front moved 8.0 cm from the baseline. The centre of spot 1 is 3.6 cm above the baseline and the centre of spot 2 is 5.2 cm above the baseline.
   Calculate the Rf value of spot 2 and explain how it can be used to identify the amino acid.2 marks
3. Keratin, the protein in hair, contains regions that are coiled into an α-helix. Its shape is also held by sulfur–sulfur bonds between cysteine residues.
   Describe what is meant by the primary structure and the secondary structure of a protein such as keratin.3 marks