Amino acids and proteinsEdexcel A-Level Chemistry: Mind map

Exam questions on Amino acids and proteins

1. Alanine, CH₃CH(NH₂)COOH, is a 2-amino acid. In the solid state and in neutral aqueous solution it exists mainly as a zwitterion.
   Alanine can act as both an acid and a base. Give the formula of the main species formed when alanine reacts with (i) excess dilute hydrochloric acid and (ii) excess aqueous sodium hydroxide.2 marks
2. Alanine is a 2-amino acid whose central carbon atom is bonded to four different groups. A solution containing only one enantiomer of alanine rotates the plane of plane-polarised monochromatic light. Glycine, H₂NCH₂COOH, does not rotate the plane of polarised light.
   Alanine made by a chemist in the laboratory does not rotate plane-polarised light, but alanine obtained by hydrolysing a natural protein does. Explain this difference.2 marks
3. Glycine, H₂NCH₂COOH, and alanine, CH₃CH(NH₂)COOH, can join together by condensation polymerisation to form peptides and proteins. A sample of protein is hydrolysed so that the amino acids it contains can be analysed.
   Glycine and alanine react to form a dipeptide in which the carboxyl group of glycine has reacted with the amino group of alanine. Name the type of reaction, state the small molecule lost, and give the structural formula of the dipeptide.3 marks