1.6 proteins

• Amino acids are the basic monomer units which combine to make up a polymer called a polypeptide.
• Polypeptides can be combined to form proteins
• Every amino acid has a central carbon atom which are attached to four different chemical groups:

  1. amino group (-NH2) (amino part of the name)
  2. carboxyl (-COOH) (acid part of the name)
  3. Hydrogen atom (-H)
  4. R (side) group
• amino acid monomers can form a peptide Bond to form a dipeptide
• A peptide bond of a dipeptide can be broken by hydrolysis to give two animo acids
• The sequence of animo acids in a polypeptide chain forms the primary structure of any protein
• the amino group and the C=O group form hydrogen bonds between them as they are oppositely charged
• The hydrogen bonds in a protein causes the alpha helix shape, which is known as the secondary structure
• the bonds that form the tertiary structure of a protein:

  1. disulfide bridges
  2. ionic bonds
  3. hydrogen bonds
• in a protein, the ionic bonds form between any carboxyl and amino groups that are not involved in forming the peptide bonds
• the amino acid sequence determines the 3D shape of a protein
• the quaternary structure is if there are several polypeptide chains or non-protein groups
• to test for proteins, you use the biuret test which detects peptide bonds
• how to test for proteins:

  1. add food sample
  2. add same volume of sodium hydroxide at room temperature
  3. add dilute copper sulfate an mix
  4. a positive result is blue to purple