Amino acids

• Primary Structure


  The sequence of amino acids (peptides)
• Why are there only 20 Amino acids

  There are only 20 Residues.
• What is a requirement for opitcal isomerism.

  
  

  4 different groups attached to the chiral centre
• Why does Glycine not exhibit optical isomerism

  It's residue group is a Hydrogen atom.
• Name the 4 groups in the general structure of an amino acid around the central carbon

  
  

  • Hydrogen
  • Amino
  • Carboxyl
  • Residue
• What is the structure of an D-isomer

  Amino group on the right
• What is the structue of an L-isomer

  Amino group on the left
• When the pH is acidic what happens to the amino acid groups

  The NH2 is proponated to form NH3+.
• What happens to the amino acid groups when the pH is basic.

  
  

  The COOH is depropanated to COO-.
• What is a Zwitterion

  At pH 7 (neutral), both the amino and carboxyl groups are ionised.

  Resulting in an overall neutral charge.
• What is pKa

  The pH at which half of a compound is ionised
• Write the general dissociation equilibrium equation

  HA = H+ + A-
• What is the effect when pH is above pKa.

  
  

  The reaction tends towards deprotanation.
• What is the effect if you decrease pH below pKa.

  
  

  The reaction tends towards protonation.