Factors affecting enzyme action

Factors which affect

rate of reaction in

enzyme-controlled

reactions

1. Temperature

   ‣ pH

   ‣ Substrate concentration

   ‣ Enzyme concentration

   ‣ Concentration of inhibitor

How do you measure rate of change?

Gradient

Describe effect of temp on enzyme action

• Rate of reaction increases up to the optimum temperature:

‣ Molecules have more kinetic energy.

‣ So there are more successful collisions.

‣ So more enzyme-substrate complexes are formed.

• Above the optimum temperature, rate of reaction decreases:

‣ Ionic & hydrogen bonds in the tertiary structure break.

‣ Active site changes shape.

‣ Substrate no longer complementary to active site.

‣ Enzyme-substrate complexes can’t form.

‣ Enzyme is denatured.

Define PH

• A measure of hydrogen ion concentration

What is PH calculated using?

PH = -log10(H+)

Describe effect of PH on enzyme action

• If pH is changed significantly away from the

  optimum:

  ‣ Ionic & hydrogen bonds in tertiary structure break.

  ‣ Active site changes shape.

  ‣ Active site no longer complementary to substrate.

  ‣ Enzyme-substrate complexes cannot form.

  ‣ Enzyme is denatured.

Describe effect of enzyme concentration on rate of reaction

Increased enzyme concentration…

‣ Increases chance of successful collisions.

‣ Increases chance of forming an enzyme-substrate complex

‣ Increases rate of reaction.

‣ Until addition of further enzyme has no further effect as there are

enough active sites to accommodate all the available substrate molecules.

Why has our body temp evolved to around 37 degrees?

• Other proteins apart from enzymes may be denatured at high temps

• At higher temps, any further rise in temp e.g during illness, may denature the enzymes

• Additional energy could be needed to maintain higher temperatures

Describe effect of substrate concentration

‣ Increased substrate concentration…

‣ Increases chance of successful collisions.

‣ Increases chance of forming an. enzyme-substrate complex.

‣ Increases rate of reaction.

‣ Continues until all the enzyme's active sites are full/saturated