enzymes

• what are enzymes

  organic catalysts that provide an alternative reaction pathway and increases the rate of chemical reactions by lowering the activation energy

  • reusable + not consumed in reaction 
  • specific --> 3D active site, 1 enzyme catalyses 1 reaction 
  • most enzyme-catalysed reaction are reversible
• what is a reversible reaction

  enzyme not permanently inhibited or damages

  • weak H bonds b/w enzyme + inhibitor --> break easily
  • act competitively or non-competitively
• what is an irreversible reaction

  enzyme permanently inhibited + no longer takes part in reactions

  • strong covalent bonds b/w enzyme + inhibitor → can't break
  • Act competitively
  • Irreversible inhibitors of enzymes = poison (cyanide/nerve gas)
• what is the lock and key model

  • Enzyme acts a ‘lock’ and substrate as ‘key’ 
  • Active site is exact shape of substrate
• what is the induced fit model

  • Active site doesn't have rigid shape 
  • Substrate enters active site + induces change in shape which enables optimum fit (conformational shape change - active site modified) 
  • Empty active site returns to relaxed state
• what is metabolism and the 2 different categories?

  Metabolism: all biochemical reactions in living cells → catabolic or anabolic

  Catabolic: substrates broken down (complex molecules) + energy released (exergonic) - exothermic

  Anabolic: substrates built from smaller molecules + energy req (endergonic) - endothermic
• what happens to an enzyme when it denatures

  denaturation → irreversible (active site of enzyme permanently altered + enzyme inactivated) - affects tertiary structure
• what are the 4 factors that affect enzyme activity

  A) temperature

  B) pH

  C) substrate concentration

  D) enzyme concentration

  
• what is competitive inhibition?

  inhibitor binds to active site of enzyme + prevents substrate from interacting
• what is non-competitive inhibition

  inhibitor binds to enzyme at ALLOSTERIC SITE (site other than active site) → causes active site to change shape (conformational shape change) + prevent substrate from interacting w enzyme
• what are coenzymes?

  COENZYMES: additional components req for some enzymes to enable them to catalyse a reaction (organic, non-protein molecules- ATP, NADH, NADPH)

  • Needed in photosynthesis + cellular respiration
  • Bind to active site + donate energy or molecules
  • Can be recycled
• define loaded and unloaded coenzymes

  Loaded coenzyme: coenzyme that can release stored chem energy by donating chem groups (ATP, NADH, NADPH)

  Unloaded coenzyme: loaded coenzyme that binds to enzyme + releases energy (ADP, NAD+, NADP+)
• what are the 4 important coenzymes and their purpose

  ATP → ADP (energy transfer Pi)

  NADH → NAD+ (e- and H+ transfer)

  NADPH → NADP+ (e- and H+ transfer)

  FADH2 → FAD (e- and H+ transfer)