1.8 Factors affecting enzyme action

Question 1

What 2 things must an enzyme have in order to work.

Answer 1

1) physical contact with the substrate
2) An active site which fit the substrate
Any factors affecting the rate of enzyme action usually alters one of these two things.

Question 2

What two changes are usually measured in an enzyme’s time-course?

Answer 2

1) formation of the products of the reaction
or
2) disappearance of the substrate

Question 3

Describe the time-course of enzyme action.

Answer 3

• at first there is a lot of substrate and no product.
• it is easy for the substrate to come into contact with empty active sites
• all active sites are filled at any given moment and the substrate is rapidly broken down into its products
• the amount of substrate decreases and the amount of product increases
• it becomes more difficult for substrate to come into contact with empty active sites as there are fewer substrates and the product molecules may get in the way
• the rate of substrate disappearance and product production slows and tails off
• the graph then flattens out as the substrate is eventually used up.

Question 4

how do you measure the rate of change on a graph?

Answer 4

calculate the gradient by drawing a tangent.

Question 5

Describe the effect of increasing the temperature on enzyme action.

Answer 5

• as the temperature begins to rise, the molecules gain kinetic energy resulting in more successful collisions creating enzyme-substrate complexes.
• when the temperature reaches a certain point, the hydrogen and other bonds in the enzyme begin to break, causing the enzyme and active site to change shape. at first this means the substrate fits less easily into the active site, slowing the rate of reaction.
• eventually the enzyme stops working; it is denatured. this is a permanent change and the enzyme will not function again.

Question 6

why is the body temperature around 37 degrees C despite the optimum temperature of our enzymes being 40?

Answer 6

• more energy (food) would be required to keep up with the increased metabolic rate
• other proteins may denature at higher temperatures
• any further rise in temperature (EG: illness) would denature enzymes.

Question 7

how can PH affect how enzymes work?

Answer 7

• it can alter the charges of amino acids which make up the active site so the substrate cannot attach and a complex cannot be formed.
• depending on how significant the change is, it can break the bonds which make up the tertiary structure of the enzyme, changing the shape of the active site.
  PH alterations in animals are usually small so they slow the rate but do not usually denature the enzymes.

Question 8

Describe the effect of enzyme concentration on the rate of reaction.

Answer 8

• If there is excess substrate, then adding more enzymes will increase the rate of reaction because there is more substrate than the active sites can cope with and some of the excess substrate can be acted on.
• if the substrate is limiting then any increase in enzyme concentration will have no effect.

Question 9

Describe the effect of substrate concentration on enzyme action.

Answer 9

• if the enzyme concentration is fixed and substrate concentration increases then the rate will increase, as more complexes are being formed.
• as more substrate is added the active sites will become filled until they reach maximum (V max) and the rate will plateau
• any further substrate increase will have no effect.