Proteins

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  • Proteins
    • Structure of amino acids
      • Basic monomer units, combine to make polymer
      • 20 naturally occur in protiens
      • Central carbon atom attached to amino, carboxyl, R group and a hydrogen atom.
    • Formation of peptide bond
      • Condensation reaction
      • Combines OH from carboxyl group of one amino acid with H from amino group of another amino acid
      • Two amino acids become linked by peptide bond between C atom and N atom of both amino acids
      • Can be hydrolysed to produce two amino acids
    • Structure
      • Primary: Polypeptide chain of amino acids
      • Secondary: Polypeptide coiled into alpha helix
      • Tertiary: Helices twisted/folded into 3D shape, maintained by hydrogen, disulfide and ionic bonds.
      • Quarternary: Number of polypeptide chains linked in various ways.
    • Test for proteins
      • Place a sample of solution in test tube and add equal volume of sodium hydroxide solution
      • Add a few drops of dilute copper sulfate solution and mix gently
      • Purple colouration indicates presence of peptide bonds. If not, solution remains blue.
    • Protein bonding
      • H bonds form between H atoms with slight + charge and other atoms with slight - charge. In AA, form in hydroxyl, carboxyl and amino groups, provide collective strength
      • Ionic bonds form between carboxyl/ amino groups that are part of R groups. + and - groups strongly attracted
      • Disulfide links formed between R groups of two cytesines. Strong covalent bnds
      • Hydrophobic and hydrophilic interactions cause twisting of amino aid chain which changes shape of protein

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