The effect of temperature and pH on enzyme activity 2.4.4 & 2.4.5

Question 1

What happens to the catalysed reactions when temperature is increased?

Answer 1

Kinetic energy increases - therefore;
- Successful collisions increase
- Formation of ES & EP complexes increase
- Product formation will increase
- Reaction will increase

Question 2

At what temperature level is the rate of reaction at its maximum?

Answer 2

At the OPTIMUM temperature

Question 3

What occurs if temperatures exceed the correct level?

Answer 3

Due to heavier vibrations;
- Weaker bonds (hydrogen) break, therefore the tertiary structure alters
- Active site shape changes
- Substrate can no longer fit, no ES complexes
- Rate of reaction decreases
- Enzyme is DENATURED

Question 4

Which enzymes have a low optimum temperature?

Answer 4

Psychrophilic bacteria

Question 5

Which enzymes have a high optimum temperature?

Answer 5

Thermophilic bacteria

Question 6

Why can some enzymes have a higher optimum temperature?

Answer 6

Enzymes, such as thermophilic bacteria, have heat stable proteins which contain more disulphide bonds. These bonds do not break with heat and so keep the protein molecule stable.

Question 7

What is Q10?

Answer 7

A ratio known as the temperature coefficient

Question 8

What does the Q10 describe?

Answer 8

What happens to the rate of reaction as temperature increases by 10°C.

Question 9

What is the formula for Q10?

Answer 9

(Rate of reaction at temperature T + 10°C) divided by (Rate of reaction at temperature T)

Question 10

When does the Q10 relationship not apply?

Answer 10

Above optimum temperature.

Question 11

What is the average value of Q10 in a test tube?

Answer 11

2 - which means that for every 10°C rise in temperature the rate of reaction is doubled.

Question 12

What does a change in pH refer to?

Answer 12

A change in hydrogen ion concentration.

Question 13

Are there more or less hydrogen ions in a low pH (acid)?

Answer 13

More hydrogen ions

Question 14

When is the active site at its right shape?

Answer 14

At a certain hydrogen ion concentration - the optimum pH.

Question 15

What is a buffer?

Answer 15

Something that resists changes in pH.

Question 16

How does a buffer work?

Answer 16

These chemicals can donate or accept hydrogen ions.

Question 18

What effect do increased hydrogen ions have on the charges on the active site?

Answer 18

Increased hydrogen ions alter the charges on the active site as more protons will cluster around negatively charged groups - which can interfere with the binding of the substrate molecule.

Question 19

What pH range do enzymes work in?

Answer 19

A very narrow range

Question 20

Describe renaturation

Answer 20

Small changes away from the optimum pH will slow the rate of reaction - however if pH is restored the hydrogen bonds can be restored

Question 21

Describe denaturation

Answer 21

When enzymes are permanently changed

Question 22

What is the optimum pH of intracellular enzymes?

Answer 22

Close to pH 7.

Question 23

What is the optimum pH of extracellular enzymes?

Answer 23

They have different values, e.g. pepsin in the stomach = pH 1-2, whereas amylase in saliva = pH 7-8.