L7-9 quiz

• in a globular protein, a leucine residue would most likely be found

  on the interior
• parallel beta strands are usually connected by:

  an alpha helix
• the peptide sequence AMHLCKFQ forms an alpha helix where the _ of C is hydrogen bonded to the _ of A

  NH and CO (n, n+4 rule)
• if a single Leu residue in an amino acid sequence was replaced with Asp, Val, Phe, Ala or Ile which would have the greatest impact on the structure of the protein.

  Asp, becuase of the carboxylic acid group

  
• beta strands are normally represented by flat arrows pointing

  from the N terminus to the C terminus
• amphipathic alpha helices are often found

  on the surface of proteins
• alpha helices are represented by

  spirals and cylinders
• what is an imino acid?

  has an imino group (NH) and a carboxylic acid group (COOH)
• proline is an imino acid
• antiparallel beta strands are usually connected by

  hairpin loops
• _ is an important amino acid in hairpin loops because its sidechain introduces a natural kink in the polypeptide chain

  proline
• _ is an important residue in hairpin loops because its small size prevents steric hinderance in these regions

  glycine
• what are epimers?

  Epimers are stereoisomers that differ in the configuration of a single stereogenic center
• there are _ chiral carbon atoms in the open chain form of glucose

  4
• secondary structures are heavily _ bonded

  hydrogen
• protein conformational changes can be induced by altering the

  • salt concentration
  • varying the pH
  • altering the temperature
• what are the essential amino acids

  histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine
• alpha helices, beta sheets and beta turns are examples of _ protein structure

  secondary
• disulphide bonds are formed by pairs of which amino acid?

  cysteine
• an aldotriose has:

  • D and L forms possible
  • 1 chiral centre
  • 2 enantiomers
• a 2.7nm long alpha helix (vertical distance between amino acids is 0.15nm) how many amino acids are in it


  18 (2.7/0.15=18)
• hydrogen bonding in alpha helices of proteins are stabilised between

  oxygen and hydrogen