AA, proteins and DNA

• How many different naturally occurring amino acids are there?

  20
• How many of the 20 amino acids show optical activity? Name any that don't:

  • 19
  • Glycine
• Why dosnt glycine show optical activity?

  It dosnt have a chiral carbon as its R group is another hydrogen.
• Definition of optical isomers:

  Non-superimposable, mirror images.

  Due to chiral carbon (with 4 different groups attached to it)
• Zwitterions exist in the crystalline form of the amino acid. Explain why this gives amino acids unusually high melting/boiling points?

  • Strong electrostatic forces of attraction between oppositly charged ions
• How do proteins form?

  • Form when condensation reaction between 2 amino acids occurs forming a peptide / amide bond
  • 2 AA = dipeptide
  • 3 AA = tripartite
  • Many AA = polypeptide
• By looking at the tertiary structure of a protein, how may a change in pH affect an ionic bond?

  • High pH would just have COO-
  • Low pH would have the NH3+
  • Need both of them for ionic bond
• Many proteins are only active over a very narrow pH range. Explain how?

  Without the ionic bond the protein would denature so it only has the ionic bond at a specific pH range
• What happens during the hydrolysis of proteins?

  • The secondary and tertiary structure rapidly break down causing the chain to unravel.
  • The chain is then hydrolysed at each peptide link so it can split into its amino acids
• What is DNA made up of?

  • Deoxyribose sugar
  • Phosphate group
  • Nitrogenous base
• Give the structure of DNA?

  • Double helix
  • Double-stranded held together by hydrogen bonds
• Name one anticancer drug:

  Cisplatin
• State one potential problem with its use of cisplatin and suggest a way in which it can be administered so that this problem is minimised:

  • Inhibit replication of healthy cells
  • Low dosage and take breaks in between treatments
• How can a substrate bind to active site:

  • Van der waals
  • Hydrogen bonds
  • Ionic bonds
• What happens if there are two enantiomers of a molecules trying to bind to an active site?

  • The active site is highly stereospecific
  • If 2 enantiomers of a molecule are present an enzyme can only catalyses the reaction for one of the enantiomers
• What is an enzyme inhibitor?

  A molecule which will either bind to the active site or distort its shape, so it cannot work
• What are some uses of enzyme inhibitors?

  • Blocking enzyme activity
  • Treating diseases and metabolic problems