1.9 - Enzyme Inhibition

• enzyme inhibitors

  substances that directly or indirectly interfere with the functioning of the active site of an enzyme and so reduce its activity
• uses of inhibitors

  poisons and drugs
• irreversible inhibitors

  cause covalent modification of an enzyme so its activity is permanently reduced
• types of reversible inhibitors

  competitive

  non-competitive

  uncompetitive
• how competitive inhibitors work

  they have a similar shape to the substrate so compete with substrate for active site - they block it so no substrate fits thus reducing enzyme activity

  inhibitor isn't permanently bound to active site so substrate can occupy the active site still
• what determines the effect inhibitor has on enzyme activity 

  the difference between concentration of inhibitor and concentration of substrate
• high inhibitor concentration

  enzyme activity falls as inhibitors will fill up more active sites
• high substrate concentration

  increases rate of reaction as there's a higher chance of substrate getting to the active site rather than the inhibitor

  effect of inhibitor is reduced
• how non-competitive inhibitors work

  they bind to the enzyme somewhere that's not the active site causing enzyme, and active site, to change shape so substrates can no longer bind to it so enzyme activity is reduced

  don't compete with substrate because they have a different shape
• how increasing substrate concentration affects effect of non-competitive inhibitors

  won't decrease effect of inhibitor because inhibitor and substrate aren't competing for active site so enzyme activity will still be inhibited
• uncompetitive inhibitors

  bind to enzyme substrate complex
• metabolic pathway

  a series of reactions in which each step is catalysed by an enzyme
• how optimum conditions for certain enzymes are maintained

  enzymes that control a pathway are often attached to the cell membrane of the organelle in a specific sequence and inside the organelle
• how a steady concentration of a certain chemical is kept

  the same chemicals may be an inhibitor of an enzyme at the start of the metabolic pathway
• positive effects of inhibitors

  medicines

  used to control a reaction effectively

  effects are only short term if reversible

  could be used to stop unwanted substrate from being broken down

  can be used as an advantage to increase survival in the animal kingdom
• negative effects of inhibitors

  effects can be irreversible

  could cause disease in itself

  can kill

  effects are only short term if reversible
• snake vernom - inhibitor name

  fasciculation (a protein)
• snake venom - function

  inhibits acetylcholinesterase - enzyme that degrades a neurotransmitter (acetylcholine)
• snake venom - how inhibitor works

  fasciculation acts as a competitive inhibitor so prevents acetylcholine from being broken down after an impulse transmission
• effect of snake venom

  in muscles fasciculation stops nerve impulses from being transmitted so stop muscle contraction which will lead to flaccid paralysis
• cyanide poisoning - inhibitor name

  potassium cyanide
• function of potassium cyanide 


  inhibits cytochrome oxidase - a vital respiratory enzyme found inside mitochondria
• how potassium cyanide works

  cytochrome oxidase normally combines hydrogen and oxygen to form water and allow ATP production

  potassium cyanide non-competitively inhibits the enzyme changing the shape of the active site so no ATP creation
• effects of potassium cyanide

  reactions that require ATP are no longer supplied and the body eventually has no energy supply causing total cell failure and death
• antifreeze poisoning treatment - inhibitor name

  ethanol
• function of ethanol in antifreeze poisoning treatment

  ethylene glycol is found in antifreeze and if ingested can be broken down by alcohol dehydrogenase forming extremely toxic oxalic acid leading to death

  ethanol prevents this
• how ethanol works in antifreeze poisoning treatment

  ethanol competitively inhibits alcohol dehydrogenase preventing ethylene glycol from interacting with alcohol dehydrogenase
• effect of ethanol in antifreeze poisoning treatment

  less oxalic acids produced so ethylene glycol is excreted
• HIV protease inhibitor name

  protease inhibitors

  variations under reserach
• function of protease inhibitors

  competitively inhibits HIV virus protease enzymes which the virus uses to cut viral RNA into smaller pieces to implant genes into host cells DNA and replicate
• how protease inhibitors work

  inhibitor binds with HIV protease enzymes active site preventing viral RNA from binding so it's not cut so can't be implanted into host's DNA so no replication

  competitive inhibition
• effect of protease inhibitors

  host cell can be infected by HIV but can't be hijacked into making more HIV copies
• malonate

  competitively inhibits succinate dehydrogenase (respiratory enzyme) so reduces ATP production