Amino acids

• Polypeptides are polymers of amino acid monomers. After ptm, we call this polypeptide chain a protein
• Amino acid structure


  -Central carbon

  -An NH2 (amine) group

  -A COOH (acid) group

  -A singular hydrogen atom

  -A variable R' group
• R Groups


  R groups' decide the charge on the amino acid.

  They can vary by

  • Size
  • Charge
  • Shape
  • Chemical reactivity
  • Hydrogen bond capacity
• Acidic amino acids


  Negatively charged and has an R group with COOH
• Basic amino acids


  Positively charged and has an R group with NH2
• Polar amino acids


  Slightly charged and has an R group with OH
• Hydrophobic amino acid


  No charge and has an R group with hydrocarbons(CH...)
• what reaction must occur to join amino acids?

  enzyme controlled condensation
• Condensation rection


  A water molecule is made by taking the OH from the COOH from one amino acid and the H from NH2 of the next amino acid.
• Peptide bond


  O=C-N-H
• Primary structure


  The sequence in which amino acids are synthesised into polypeptides. Determines the proteins function.
• Secondary structure


  Decided by hydrogen bonding along the backbone of the protein strand. Can be folded into either; alpha helix, beta-pleated sheets (parallel or anti-parallel) or turns.
• Tertiary structure


  3D and is caused by interactions between R groups and amino acids.
• 5 types of interactions which affect tertiary structure.

  Hydrophobic interactions

  ionic bonds

  hydrogen bonds

  london dispersion forces

  disulphide bridges
• Disulphide bridge


  covalent bonds between R groups which contain sulphur
• how does higher temperature affect tertiary structure?


  A higher temperature will cause the structure to become destabilised as the chain 'shakes' which breaks weaker bonds
• how do pH changes affect tertiary structure?


  A change in pH will affect the ionisation of the acidic and basic R groups and change the charge they carry so they can no longer bond directly.
• Quaternary structure


  Exists in proteins with 2 or more sub-units.
• Why are R groups important?

  They determine the structure of the protein, Allow ligands to bind and determine the location of the protein within the cell