Proteins: general properties of proteins

• Amino acids

  Monomers from which proteins are made
• Dipeptides

  2 amino acids joined by a peptide bond
• Polypeptides


  Many amino acids joined together
• Amino acid

  • General structure: H₂N-COOH with variable side chain/group
• Formation of a peptide bond

  Condensation reaction between 2 amino acids
• Functional protein

  May contain one or more polypeptides
• Primary (1°) structure

  Order and number of amino acids in a protein. This primary structure contains the initial sequence of amino acids and will therefore determine the proteins function in the end
• Secondary (2°) structure


  • Shape that the chain of amino acids make - either alpha helix or beta pleated sheet
• Tertiary (3°) structure


  • 3D structure of protein and is formed from further twisting and folding. Different bonds maintain the structure: Disulfide bridge, Ionic bonds and Hydrogen bonds.
• Quaternary (4°) structure


  • Proteins made of 2+ polypeptide chains held together by more hydrogen, ionic and disulfide bonds
• Biuret test


  Detects presence of peptide bonds - protein present: purple colour, negative: stays blue
• Groups in the amino acid structure

  Carboxyl, Amine , Side chain