Enzymes

Question 1

What are enzymes?

Answer 1

A biological catalyst that speeds up chemical reactions

Question 2

What is the enzyme’s active site?

Answer 2

Part of an enzyme where the substrate molecule binds to it
It has a specific shape

Question 3

What is activation energy?

Answer 3

The amount of energy needed to be supplied to the chemicals before the reaction will start

Question 4

How do enzymes lower the activation energy?

Answer 4

When an enzyme substrate complex is formed the activation energy is lowered because:
- if 2 substrate molecules need to be joined, being attached to the enzyme holds them close together reducing any repulsion so they can bond more easily
- if the enzyme is catalysing a breakdown reaction, fitting into the active site puts a strain on bonds causing substrate molecules to break more easily

Question 5

What happens if the activation energy is lower?

Answer 5

Reactions can take place at lower temperatures which speeds up reactions

Question 6

Describe the lock and key model

Answer 6

Substrate fits into active site. Enzyme is unchanged after reaction

Question 7

Describe the induced fit model

Answer 7

Active site of an enzyme changes shape when an enzyme substrate complex is formed. Enzymes only fit to one particular substrate

Question 8

What does the induced fit model show?

Answer 8

Explains why enzymes are so specific

Question 9

Explain the structure enzymes relating to their tertiary structure

Answer 9

Very specific (only 1 substrate complementary to active site)
Active site is determined by the enzymes tertiary structure
Each different enzyme has a different tertiary structure
If tertiary structure is altered (by pH or temperature) the shape of the active shape will be changed
Mutations in primary structure can cause changes in tertiary structure

Question 10

What are the four factors that affect enzyme activity?

Answer 10

1. Temperature
2. pH
3. Enzyme concentration
4. Substrate concentration

Question 11

How does temperature affect enzyme activity?

Answer 11

An increase in temperature means more vibration and collision. If temp goes above a certain level the vibrations will break bonds holding the enzyme in shape. The active site will change shape and the enzyme will be denatured.

Question 12

How does pH affect enzyme activity?

Answer 12

Above and below optimum pH, H+ and OH- ions can mess up ionic and hydrogen bonds that hold the enzymes tertiary structure in place. Denatures enzyme

Question 13

How does enzyme concentration affect enzyme activity?

Answer 13

More enzymes mean more substrate collision and an increase rate of reaction. If the substrate is limited then there is more than enough enzymes to deal with all available substrate so adding more enzymes will have no further effect

Question 14

How does substrate concentration affect enzyme activity?

Answer 14

Increasing the substrate concentration increases the rate of reaction as there are more collisions. This is only up to a saturation point when all the active sites are full. Substrate concentration decreases with time which decreases the rate of reaction

Question 15

What is a competitive inhibitor?

Answer 15

A molecule with a similar shape to substrate molecule, meaning it competes with substrate to bind to active site.

Question 16

How does increasing the concentration of competitive inhibitors affect substrate molecules?

Answer 16

Active sites are blocked and nearly all taken up

Question 17

How does increasing the substrate concentration affect competitive inhibitors?

Answer 17

Increases the chance of substrates getting to active site before inhibitors

Question 18

What is a non-competitive inhibitor?

Answer 18

Molecules that bind to enzymes away from their active site causing the active site to change shape so substrate can no longer bind to it

Question 19

How does increasing the substrate concentration affect non-competitive inhibitors?

Answer 19

Won’t make any difference to the rate of reaction as enzyme will still be inhibited