Enzymes

What do enzymes do?

They speed up rate of reactions by acting as catalysts (do not get used up). Catalyse specific metabolic reactions at a cellular level e.g. digestion in mammals.

What are enzymes?

They are proteins with 3D structure, have an active site which has specific shape, can only bind to specific substrate. After enzyme-substrate complex is formed, the products leave the active site and the enzyme goes onto make more ES-complexes.

What do enzymes do to aE?

Activation energy is lowered, allow reactions to happen at lower temperatures as either hold substrates close together, reducing repulsion and allowing them to bond more easily, or put more strain on bonds of substrate allowing them to break apart more easily.

What is the original model?

Lock and key, shape of active site is exactly complimentary to substrate.

What is the new model?

Induced fit model, shape of active site is not exactly complimentary to substrate. When substrate collides, the active site can change shape slightly to fit around the substrate.

What are the factors affecting enzyme action?

Enzyme concentration, substrate concentration, temperature and pH.

What is the effect of enzyme conc?

Increases number of active sites available for substrates to collide with. More ES-complexes can form. Rate of reaction will increase until amount of substrate becomes limiting factor, as more enzymes than substrates. Increasing enzyme will no longer have an effect.

What can the gradient of enzyme concentration graph tell us?

Used to calculate how fast the rate is changing.

What is the effect of substrate concentration?

Increase rate of reaction, more substrates available. More ES-complexes. Rate of reaction will slow when enzyme conc becomes limiting factor. When all active sites are occupied (saturation point) substrate no further effect.

What is the effect of temperature?

Rate increases as more kinetic energy so molecules move faster, increasing collisions, more ES-complexes formed. Each enzyme has optimum temp, once been reached temp will decrease. At high temps enzyme vibrate too much, bonds broken which maintain tertiary structure. Active site changes shape so no more ES complexes. Enzyme denatured.

What is the effect of pH?

All enzymes have optimum pH, most work best at 7 but some at 2 (pepsin in stomach). Above and below optimum pH, H+ and OH- ions disrupt the ionic and hydrogen bonds holding the tertiary structure. At extremes of pH, active site changes shape so substrate no longer fits. Enzyme denatured.

What can prevent or slow enzyme activity?

Enzyme inhibitors.

Name 2 types of inhibitors.

Competitive and non-competitive.

What is a competitive inhibition?

Have similar shape to substrate, compete with substrate to bind to active site, block the active site so substrate cannot bind.

What is a non-competitive inhibition?

Do not bind to active site as has different shape to substrate (so does not compete) bind to a site away from active site, the allosteric site. Causes active site to change shape so no longer complimentary to substrate.

What is the difference between increase substrate conc for comp and non-comp inhibitors?

Comp= increasing substrate conc will increase rate of reaction, will reverse the effects of a competitive inhibitor as substrate will out-compete the inhibitor for active site.

Non-comp= no effect to rate of reaction, they cannot bind to the active site either way.

What can enzyme inhibitors be used for?

They can be used in drugs and poisons.