1.4.1 General properties of proteins

• Describe / draw the general structure of an amino acid

  ● COOH = carboxyl group

  ● R = variable side chain / group

  ● H2N = amine group

  
• How many amino acids are common in all organisms? How do they vary?

  The 20 amino acids that are common in all organisms differ only in their side group (R)
• Describe how amino acids join together

  ● Condensation reaction

  ● Removing a water molecule

  ● Between carboxyl / COOH group of one and amine / NH2 group of another

  ● Forming a peptide bond

  
• What are dipeptides and polypeptides?

  ● Dipeptide - 2 amino acids joined together

  ● Polypeptide - many amino acids joined together A functional protein may contain one or more polypeptides
• Describe the primary structure of a protein


  Sequence of amino acids in a polypeptide chain, joined by peptide bonds

  
• Describe the secondary structure of a protein

  ● Folding (repeating patterns) of polypeptide chain eg. alpha helix / beta pleated sheets

  ● Due to hydrogen bonding between amino acids

  ● Between NH (group of one amino acid) and C=O (group)

  
• Describe the tertiary structure of a protein

  ● 3D folding of polypeptide chain

  ● Due to interactions between amino acid R groups (dependent on sequence of amino acids)

  ● Forming hydrogen bonds, ionic bonds and disulfide bridges

  
• Describe the quaternary structure of a protein

  ● More than one polypeptide chain

  ● Formed by interactions between polypeptides

  (hydrogen bonds, ionic bonds, disulfide bridges)

  
• Describe the test for proteins

  1. Add biuret reagent (sodium hydroxide + copper (II) sulphate)

  Positive result = purple / lilac colour (negative stays blue) → indicates presence of peptide bonds