AQA Chem4: Amino Acids

Revision notes on amino acids from the organic section of AQA Chem4

  • Created by: anna
  • Created on: 06-06-13 10:37

Amino Acids

  • there are 20 important naturally occuring amino acids
  • all amino acids have two functional groups, an amine -NH2 and a carboxylic acid -COOH
  • a typical amino acid is a white crystalline solid with a melting point of 200C
  • they can exist as zwitterions which are ions with a permanent positive and negative charge but which are neutral overall,
  • these charges mean they can pack together as an ionic lattice
  • in acidic conditions the carboxylic acid part is protonated so the molcule has an overall positive charge
  • in basic conditions the amino group is deprotonated so the molecule has an overall negative charge
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Peptides, Polypeptides and Proteins

  • amino acids link together to form peptides
  • molecules containing up to about 50 amino acids are referred to as polypeptides
  • when there are more than 50 amino acids they are proteins
  • the amine group of one amino acid will react with the carboxylic acid of another to give an amide or peptide linkage
  • compounds formed by the linkage of 2 amino acids are called dipeptides and those formed by the linkage of 3 amino acids are tripeptides
  • you can use hydrolysis to break down a polypeptide into the individual amino acids
  • to separate a mixture of amino acids you can use column chromatography and to identify the different amino acids you can use paper chromatography
  • proteins have complex shapes which are held in place by hydrogen bonds
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