Enzymes

Question 1

What is activation energy?

Answer 1

The minimum amount of energy needed to activate a reaction

Question 2

What effect do enzymes have on activation energy

Answer 2

Enzymes lower activation energy

Question 3

Name the molecule that an enzyme acts on

Answer 3

Substrate

Question 4

Where on an enzyme does a substrate bind?

Answer 4

Active site

Question 5

What does an enzyme and substrate form when they bind together?

Answer 5

Enzyme-substrate complex (ES complex)

Question 6

Name two theories of enzyme action

Answer 6

Lock and key hypothesis

Induced fit hypothesis

Question 7

Explain the lock and key hypothesis

Answer 7

The substrate is the key, the enzymes active site is the lock. The substrate fits into the active site of the enzyme as it is complementary in shape

Question 8

Name a key difference between the lock and key hypothesis and the induced fit hypothesis

Answer 8

The enzymes active site changes shape in the induced fit hypothesis, whereas the shape of the active site remains the same in the lock and key hypothesis

Question 9

What biological molecule are enzymes?

Answer 9

Proteins

Question 10

What is meant by a biological catalyst?

Answer 10

Enzymes - speed up the rate of reaction in living organisms

Question 11

Why are enzymes effective in small quantities?

Answer 11

They can be used over and over again

Question 12

Name 4 factors that affect the rate of an enzyme controlled reaction

Answer 12

1. Temperature
2. pH
3. Concentration of enzyme
4. Concentration of substrate

Question 13

DESCRIBE the effect of temperature on an enzyme controlled reaction

Answer 13

Rate of reaction increases, peaks, then decreases

Question 14

EXPLAIN the effect of temperature on an enzyme controlled reaction

Answer 14

Increasing temperature increases the kinetic energy of molecules so more enzyme-substrate collisions occur. More enzyme substrate complexes (ES complexes) form.
Above optimum temperatures, the enzyme denatures (shape of the active site changes irreversibly), less or no ES complexes form

Question 15

DESCRIBE the effect of pH on an enzyme controlled reaction

Answer 15

Rate of reaction increases, peaks, and then decreases

Question 16

EXPLAIN the effect of temperature on an enzyme controlled reaction

Answer 16

pH alters the charges on amino acids that make up the active site. The active site is no longer complementary in shape to the substrate - the enzyme has denatured

Question 17

DESCRIBE the effect of substrate concentration on an enzyme controlled reaction

Answer 17

As the substrate concentration increases so does the rate of reaction up to a point when the rate of reaction plateaus

Question 18

EXPLAIN the effect of substrate concentration on an enzyme controlled reaction

Answer 18

As the substrate concentration increases, more substrate molecules are available to collide with an enzymes active site forming ES complexes.
The rate of reaction becomes limited by the concentration of enzyme as the enzymes are working at maximum capacity when the graph plateaus

Question 19

What is meant by the maximum capacity/turnover of an enzyme?

Answer 19

The maximum rate at which all the enzymes can work

Question 20

What is pH a measure of?

Answer 20

The hydrogen ion concentration

Question 21

Explain why enzymes work less well at lower temperatures?

Answer 21

Lower temperatures reduce the amount of kinetic energy which results in less collisions and less ES complexes

Question 22

Explain why high temperatures may prevent enzymes from functioning

Answer 22

High temperatures denature enzymes - alter the shape of the active site irreversibly

Question 23

What is meant by the induced fit hypothesis?

Answer 23

Binding of the substrate changes the shape of the enzymes active site, making the enzyme able to react.
The enzymes active site returns to its original shape once the products have been released

Question 24

Name two types of inhibitors

Answer 24

Competitive and non-competitive

Question 25

Explain how competitive inhibitors work

Answer 25

Competitive inhibitors are molecules that are complementary in shape to an enzymes active site.
They compete with substrate molecules for the active site

Question 26

Explain how non-competitive inhibitors work

Answer 26

Non competitive inhibitors bind to a site other than the active site on an enzyme (allosteric site).
This produces a change in the shape of the active site so substrate molecules can no longer bind

Question 27

What effect do competitive inhibitors have on the rate of an enzyme controlled reaction?

Answer 27

Rate of reaction is slower, maximum rate of reaction can be achieved depending on the concentration of the inhibitor

Question 28

What effect do non-competitive inhibitors have on the rate of an enzyme controlled reaction?

Answer 28

Non-competitive inhibitors reduce the rate of reaction. The maximum rate of reaction is not reached as the change in the shape of the active site is permanent