A-LEVEL BIOLOGY OCR NOTES
enzymes
Enzymes
- Enzymes are biological catalysts that speeds up the rate of reaction and remains unchanged and reusable at the end of the reaction.
- They lower the activation energy of the reaction.
- The lock and key model proposed that each substrate is a key that only fits a specific lock or enzyme. The alternative induced fit model has been proposed (below)
- The specificity of enzymes is due to the tertiary structure of its active site, allowing complementary binding to substrates.
- Enzymes catalyse both intracellular and extracellular reactions that determine structures and functions from cellular to whole organism level.
- Catalase intracellularly breaks down hydrogen peroxide into water and oxygen
- Amylase is secreted from the salivary glands and pancreas to extracellularly break down starch. Requires Cl- cofactor
- Trypsin is secreted from the pancreas to extracellularly break down proteins
- Some enzymes are synthesised in an inactive precursor form and need to be activated e.g. another enzyme removes part of the molecule in trypsin, forming the correct active site shape
- Some enzymes require a cofactor, which is a substance which must be present to enable an enzyme to catalyse a reaction at the appropriate rate.
- A prosthetic group is permanently bound e.g. Zn^2+ bound to carbonic anhydrase CO2 ⟷ H2CO3 ⟷ H^+ + HCO3
- A coenzyme forms temporary associations and are derived from vitamins.
- Factors affecting enzyme activity include:
- The temperature coefficient (Q10) for a specific reaction is the effect of a 10°C rise in temperature on the rate of the reaction
