Enzymes 2

• What is a transition state analogues?


  compound that inhibit enzyme, largely competetive
• what binds with a higher affinity TSA or substrate?

  TSA
• what is a transition state analogues example?


  yeast aldolase, in glycolysis
• what is Km?


  michaelis constant
• what does low km a mean?

  high affinity with active site and molecule
• what is ki?


  same as km for inhibitor
• how to tell how much stronger is the TSA than natural transition state?

  Km / Ki
• what is the first step in catalysis?

  formation of enzyme-substrate complex
• who comes up with the induced-fit hypothesis?

  Koshland
• where do the catalytic amino acids in the active site come from?


  different locations in the primary amino acid sequences
• how does the substrates bind in the active site of enzyme?

  multiple weak interactions
• What type of bond does not form with enzyme and substrate?

  covalent
• what is the difference between active site and catalytic site?

  Active site: where substrate binds and reactions occur. Catalytic site: where catalysis takes place within the active site.
• what makes up active site?

  ATP binding-site, substrate binding site, catalytic residues (catalytic site)
• how does the active site facilitate reactions?

  Entropy effect

  Orbital steering
• what is the entropy effect?

  Substrates held next to each other or catalytic groups for increased length of time
• what is orbital steering?

  best orientation of substrate relative to catalytic groups
• what is induced fit?


  Maximal binding involves changes to conformation of E and S
• why do enzymes react with any molecule?


  Induced-fit
• how does induced fit improve specifity?


  open conformation allows substrate binding.

  closed conformation reconstitutes catalytic site
• what are coenzymes?

  Non-protein organic that binds at catalytic site, normally reversible bound, few permanent prosthetic groups
• What is an inactive enzyme known as?

  apoenzyme
• what is an active enzyme called?

  holoenzyme
• What is a cofactor?

  inorganic mostly metals , that bind NOT at the catalytic site, bind near on in active site
• what do cofactors do?

  • assist in substrate binding
  • stabilisation of transititon state
  • orientation
  • stabilises the catalytic site
  • Can participate general acid-base catalysis and oxidation-reduction
• what are the 3 reaction mecahnisms?

  acid-base catalysis, covalent catalysis, electrostatic catalysis
• what is covalent catalysis?

  covalent link is formed between substrate and amino acid in catalytic site
• which amino acid is in acid-base catalysis?

  Histidine
• what is electrostatic catalysis?

  favours formation of transition state by stabilizing its structure