1.4.1 general properties of proteins

• describe the generals structure of an amino acid

  COOH = carboxyl group

  R = variable side chain/group

  H2N = amine group
• how many amino acids are common in all organisms? how do they vary?

  the 20 amino acids that are common in all organisms differ only in their side group (R)
• describe how amino acids join together

  condensation reaction

  by removing a water molecule

  between a carboxyl/COOH group of one and amine/H2N of another

  forming a peptide bond
• what are dipeptides and polypeptides

  dipeptide - 2 amino acids joined together

  polypeptide - many amino acids joined together
• describe the primary structure of a protein

  sequence of amino acids in a polypeptide chain, joined by peptide bonds
• describe the secondary structure of a protein 


  folding (repeating patterns) of polypeptide chain e.g alpha helix/beta pleated sheets

  due to hydrogen bonding between amino acids

  between NH (group of one amino acid) and C=O (group)
• describe the tertiary structure of a protein

  3D folding of polypeptide chain

  due to interactions between amino acid R groups (dependent on sequence of amino acids)

  forming hydrogen bonds, ionic bonds and disulphide bridges
• describe the quaternary structure of a protein

  more than one polypeptide chain

  formed by interactions between polypeptides (hydrogen bonds, ionic bonds, disulphide bridges)
• describe the test for proteins

  add biuret reagent (sodium hydroxide +copper (II) sulphate)

  positive result = purple/lilac colour (negative stays blue) which indicates presence of peptide bonds