Proteins

• protein’s monomer -> amino acid
• amino acid are made up of H , N , C , O
• NH2 is the amine group
• COOH is the carboxyl group
• R represents a variable side chain which is different for each of the 20 amino acids
• Peptide bond - a condensation reaction between two amino acids
• Dipeptides are formed by the condensation reaction of two amino acids
• Polypeptides are formed by the condensation reaction of many amino acids
• the general structure of a amino acid :

  • Carboxyl group ( COOH )
  • R variable
  • amine group ( NH2 )
• Test for proteins in a sample :

  1. add equal volume of sodium hydroxide to a sample at room temperature
  2. add drops of dilute copper sulfate solution , swirl to mix
  3. POSITIVE RESULT : colour changes from blue to purple NEGATIVE RESULT : solution remains blue
• there are 20 amino acids and they differ by side ' R ' group
• condensation reaction forms peptide bond
• dipeptide : 2 amino acids
• polypeptide : 3 or more amino acids
• two types of secondary protein structure

  • a helix
  • b pleated sheet
• a helix :

  all N-H bonds on same side of protein chain

  spiral shape

  H-bonds parallel to helical axis
• b-pleated sheet :

  N-H an C=O groups alternate from one side to the other
• disulfide bridges : strong covalent S-S bonds between molecules of the amino acid cysteine
• ionic bonds : relativley strong bonds between charged R groups
• hydrogen bonds : numerous & easily broken
• Globular proteins :

  spherical and compact

  involved in metabolic processes
• fibrous proteins :

  • form long chains or fibres
  • insoluble in water
  • use for structure and support
• enyzmes are biological catalysts
• induced fit model of enzyme action :

  • shape of active site is not directly complementary to substrate and is flexible
• lock and key : rigid shape of active site complimentary to only 1 substrate
• competitive inhibitors:

  • similar shape to substrate , bind to active site
• non-competitive inhibitors :

  • bind at allosteric binding site
• structure of proteins is determined by the order and number amino acids, bonding present and the shape of the protein