Factors

• Factors affecting enzymes

  • pH
  • temperature
  • enzyme concentration
  • substrate concentration
  • inhibitors
• extreme pH

  • extreme pH has excess H+ or OH-
  • this can cause hydrogen and ionic bonds to break within the tertiary structure of enzymes
  • this changes the tertiary structure, and then the shape of the active site
  • this prevents the formation of an enzyme-substrate complex
  • the enzyme is denatured
• pepsin is found in the stomach

  optimum pH of 2
• Optimum conditions

  • allows catalysis at the maximum rate
  • faster rate of reaction
• Low temperatures

  • less kinetic energy
  • molecules move less
  • lower frequency of successful collisions
  • less enzyme-substrate complexes form
  • collisions have less energy too
  • less likely for bonds to form or break
• Increasing temperature

  • provides more kinetic energy
  • particles move more
  • higher frequency of successful collisions
  • more enzyme-substrate complexes form
  • collisions have more energy
  • more likely for bonds to break or form
• Too high temperatures

  • vibrations in bonds increase
  • strain on bonds
  • hydrogen bonds break within structure, changing shape of the enzyme and its active site, now denatured
  • no more enzyme-substrate complexes can form
• Temperature co-efficient Q10


  $Q10\ =$$\ \frac{rate\ of\ reaction\ \left(t+10°C\right)}{rate\ of\ reaction\ \left(t\right)}$
• Optimum 


  • varies on habitat
  • varies on how an organism has adapted
  • e.g. some bacteria have thermostable enzymes as they live in hot springs
• Optimum tempertature

  • most enzymes denature above 60°C
  • humans at 37°C, above 40°C can cause denaturation
• Enzyme concentration


  • higher enzyme conc, greater number of active sites, higher chance of ES complexes forming
  • rate increases until limiting factor is reached, like substrate concentration
• Substrate concentration


  • higher substrate concentration, higher chance of ES complexes forming
  • rate increases until limiting factor is reached, like enzyme concentration
• Vmax


  • maximum rate of reaction for any given enzyme concentration, temp and pH
  • when substrate concentration is not longer the limiting factor
• Reversible inhibitors

  • form weak hydrogen bonds to the enzyme
  • easy to break bonds to remove it
• Competitive inhibitors

  • bind to the active site as they have a similar shape to the substrate
  • effect can be countered by increasing substrate concentration
• Non-competitive inhibitors

  • binds to the allosteric site
  • changes the shape of the active side
  • increasing substrate concentration has no effect
• reversible inhibitors act as regulators in metabolic pathways


  to tightly control and balance them
• End-product inhibition

  • final product of a metabolic pathway can inhibit an enzyme that acts earlier on in the pathway
  • when product levels fall, the enzyme can catalyse reactions again so the final product is produced again - feedback loop!
• Enzyme inhibition

  • inactive precursors so cells are not damaged
  • inhibitors can be removed when the enzyme needed
• Non-reversible inhibitors

  • form covalent bonds to the enzyme
  • requires a lot of energy to remove
  • results in complete inactivation of the enzyme
  • reactions stop completely
  • more of the enzyme must be produced to overcome
• Metabolic poisons that stop metabolic reactions

  • cyanide - inhibits cytochrome C oxidase, involved in respiration
  • arsenic - inhibits pyruvate dehydrogenase, involved in respiration
  • lead - ferrochelatase, involved in haem production
• Medicinal uses of inhibitors

  • antibiotics - penicillin inhibits transpeptidase, catalyses formation of protein in bacterial cell walls
  • antiviral drugs - inhibits reverse transcriptase, preventing replication of viral DNA, preventing viruses from respiring