protein structure

• What is the term given to the molecule formed when two amino acids join together?

  dipeptide
• what bond is formed when two amino acids join together?

  peptide bond
• What is the term for the molecule formed when many amino acids are joined by peptide bonds?

  polypeptide
• Proteins consist of 1+ polypeptides, arranged as a macromolecule. All contain C,H, N, O.
•  Proteins have four levels of structure- primary, secondary, tertiary and quaternary
• Primary structure only involves peptide bonds.

  A linear sequence of amino acids joined together.

  Particular amino acids in a sequence influence how the polypeptide folds to give the protein’s shape.

  
• secondary structure - Can be an alpha helix or a beta pleated sheet.

  Bonding of the peptide backbone (no involvement of the variable group) causes the amino acids to fold into a repeating pattern.

  we are involving hydrogen bonds

  
• bonding in alpha helix

  Hydrogen bonds form within the amino acid chain. This pulls it into a coiled shape called an alpha helix.

  
• bonding in beta pleated sheets

  Polypeptide chains may lie parallel to each other. Hydrogen bonds can then form between these chains forming a sheet structure.

  
• tertiary structure - 3D folding of a helix or beta sheet due to side chain interactions of the R variable groups.

  These can be:

  • Hydrophobic and hydrophilic interaction

  • Hydrogen bonds

  • Ionic bonds

  • Disulphide bonds/bridges

  
• bonding in tertiary

  • Hydrogen bonds are the weakest bonds formed.
  • Disulphide bridges are strong, covalent bonds. They only form between cysteine amino acids/ sulphur containing R groups
  • Ionic bonds form between oppositely charged R groups

  This produces a complex protein with a specialised function

  
• strongest

  1. Disulphide bridges
  2. ionic bonding
  3. hydrogen bonding

  weakest
• quaternary structure - The interaction of two or more protein subunits.

  Interactions are the same as in tertiary structure but are between protein subunits rather than within the polypeptide molecule. Protein subunits don’t need to be identical.

  
• This is haemoglobin. It is made up of 4 subunits, made of 2 identical subunits. This is a quaternary protein structure.