Enzymes Flashcards
Metabolism
Combination of anabolic (Building up) and catabolic (Breaking down) reactions, catalysed by enzymes
Intracellular enzymes
- Some exist in solution inside cells e.g in cytoplasm
- Some are membrane bound e.g ATP synthetase
Extracellular enzymes
Act outside of cells and are secreted by exocytosis
Active site
A cleft on an enzyme molecule with a specific 3D shape into which a specific substrate molecule fits during a metabolic reaction
Induced fit theory shown by lysozyme
- Active site is not complementary
- Shape alters to bind to substrate
- Enzyme brings substrate closer and holds it in place for reaction
- Therefore “fit” has been “induced”
- Altering shape strains substrate molecule bonds
- Lowers the activation energy needed to break the bond
Lock and Key model
Enzyme and substrate are complementary
Activation energy and Catalysis
Activation energy:
- The minimum energy that must be put into a chemical system for a reaction to occur
Catalysis:
- The lowering of activation energy
Temperature’s affect on rate
- Low temperatures: Rate is slow due to less kinetic energy
- Higher temperature: Rate increases due to more kinetic energy
- Beyond optimum: Rate decreases as bonds in enzymes break and active site loses specific shape (denature)
pH affect on rate
- Minor pH changes are reversible
- Extreme pH changes are irreversible (Denaturing)
- Buffers added to experiments involving enzymes to resist changes in pH
Substrate concentration affect on rate
Low substrate concentration: Few enzyme substrate complexes form, so rate is low
Increasing substrate concentration: More enzyme substrate complexes so rate increases
More substrate than enzyme: All active sites are full so the rate can no longer increase.
Enzyme concentration affect on rate
- More enzyme substrate complexes means a increasing rate
- Rate of reaction is directly proportional to enzyme concentration
Inhibitor
Any molecule that reduces the rate of an enzyme controlled reaction
Competitive inhibitor
- Competitive inhibitor molecules have similar shape as substrate
- Block active site and reduce enzyme substrate complexes
- Effect is reduced by increasing substrate concentration
Non-competitive inhibitor
- Bind to allosteric site
- Causes conformational change of active site which is irreversible
- Slowest rate as the inhibitor does not compete for allosteric site and the change is irreversible
Immobilised enzymes
Enzyme molecules that are bound to an inert material, over which the substrate molecules move
Advantages:
- Products are not contaminated with enzymes
- Enzymes can withstand more environmental factors
- Enzymes can be reused
- Several enzymes can be used at the same time
Use:
- Removing substances from products e.g lactase
- Biosensors measuring blood glucose
