Proteins

• Proteins are made up of amino acids, which are linked together by peptide bonds.
• Amino acid structure

  
• Properties of amino acids vary because their R groups vary.
• Formation of a dipeptide

  
• Many amino acids join by peptide bonds to form polypeptides.
• Primary structure of a protein is the sequence of amino acids in a polypeptide chain.
• Secondary structure is the folding of the primary structure into alpha helices or beta sheets.
• Alpha helix:

  • Primary structure folds on itself to form a helix.
  • Each turn in the helix has ~ 4 amino acids.
  • Hydrogen bonds form between C=O and the N-H groups of amino acids.
• Beta pleated sheets:

  • The primary structure bend the chain in a zig-zag manner, with a U bend at the 6th amino acid.
  • Hydrogen bonds form between C=O and the N-H groups of amino acids, facing each other.
• Tertiary structure is the overall 3D shape of a protein when secondary structure folds and results from interactions and bonds between the R groups.
• Hydrogen bonding in tertiary structure form between R groups and opposite partial charges in either the peptide backbone or other R groups.
• Hydrophobic interactions in tertiary structure: clustering of hydrophobic groups away from water.
• Van der Waals interactions in tertiary structure: association of hydrophobic chains are further stabilised by electrical attractions.
• Ionic bonding in tertiary structure form between groups that have full and opposite charges.
• Quarternary structure is individual polypeptides are held together by the same type of bonds and interactions found in the tertiary structure.
• Structure of collagen

  • Fibrous.
  • Primary structure contains repeating sequence of amino acids, glycine, proline and hydroxyproline.
  • 3 long polypeptides held together with hydrogen bonds between chains.