Proteins

• Describe the structure of an amino acid

  There is a central carbon atom bonded to an amino group, a carboxyl group, an H group and a variable R group
• describe how a peptide bond is formed between two amino acids

  A condensation reaction occurs between the amino group of one amino acid and the carboxyl group of another amino acid, producing a molecule of water.
• describe the primary structure of a protein

  The sequence of amino acids that have been joined by the condensation reaction to form a polypeptide chain.
• describe how the secondary structure of a protein is produced

  There are hydrogen bonds between the amino group of one amino acid and the C=O group of another, forming a-helix or ß-pleated sheet.
• describe how tertiary structure of a protein is produced

  The specific sequence of amino acids in the polypeptide chain will fold into the complex 3-D tertiary structure due to different bonds between the different R-groups. These bonds are disulphide bridges, ionic bonds and hydrogen bonds.
• describe how the quaternary structure of a protein is produced

  Different polypeptide chains combine in various ways, and may also be associated with a non-protein group.
• two proteins have the same number and type of amino acids but different tertiary structure explain how

  They could have a different primary structure (sequence of amino acids) and therefore the bonds between the R-groups, such as disulphide bridges, ionic bonds and hydrogen bonds would be in different places.
• a protein can change shape due to the pH of the solution it is in explain how

  The ionic and hydrogen bonds that hold the 3-D tertiary structure in place are affected by the pH. Disruption of these bonds will therefore change the structure of the protein
• describe the biochemical test for proteins and enzymes

  Add Biurets reagent to the test solution. A positive result is from blue to purple.