2.4.1 Action of Enzymes

Question 1

What type of enzyme is catalase?

Answer 1

Intracellular enzyme.

Question 2

What does catalase breakdown that is a toxic by-product of several reactions?

Answer 2

Hydrogen peroxide.

Question 3

What type of enzyme is amylase and trypsin?

Answer 3

Extracellular enzyme.

Question 4

What does amylase catalyse?

Answer 4

The hydrolysis of starch into maltose.

Question 5

What does trypsin catalyse?

Answer 5

The hydrolysis of peptide bonds - turning big polypeptides into smaller ones.

Question 6

Where is trypsin produced?

Answer 6

By cells in the pancreas and secreted into the small intestine.

Question 7

What type of enzymes are proteins?

Answer 7

Globular proteins.

Question 8

What does the specific shape of an active site determine?

Answer 8

The enzyme’s tertiary structure.

Question 9

Why do enzymes reduce activation energy?

Answer 9

To make reactions proceed at a lower temperature, speeding up the rate of reaction.

Question 10

Why does the activation energy decrease when an enzyme-substrate complex is formed?

Answer 10

• Two substrate molecules are close together therefore reduces repulsion.
• When an enzyme catalyses a breakdown reaction, fitting into the active site puts a strain onto the bonds, therefore the molecule breaks up more easily.

Question 11

Describe the lock and key model.

Answer 11

• Substrate fits into the enzyme the same way a key fits into the lock.

Question 12

What does evidence show about the lock and key model?

Answer 12

• Evidence shows that the enzyme-substrate complex changes shape slightly to complete the fit.

Question 13

Describe the induced fit model.

Answer 13

• Substrate makes the active site change shape.

Question 14

How does temperature effect enzyme activity?

Answer 14

• The rate of an enzyme-controlled reaction increases when the temperature is increased.
• More heat = more kinetic energy = more successful collisions.
• Rise in temperature = enzyme molecules vibrate more.
• Temperature goes beyond a certain threshold, vibration breaks some of the bonds that hold the enzyme in shape.
• The active site changes shape and the enzyme and substrate can no longer fit together.
• Enzyme is denatured - no longer functions as a catalyst.

Question 15

What is the formula for temperature coefficient?

Answer 15

Rate at higher temperature/Rate at lower temperature.

Question 16

How does pH effect enzyme activity?

Answer 16

• All enzymes have an optimum pH value.
• Above and below the optimum pH value, the hydrogen and hydroxide ions found in acids and alkalis can mess up the ionic bonds and hydrogen bonds that hold up the enzymes tertiary structure in place.
• Active site then changes shape leading the enzyme to denature and no longer function as a catalyst.

Question 17

How does enzyme concentration effect enzyme activity?

Answer 17

• Increasing the concentration of the enzyme increases the rate of reaction.
• However, if the amount of substrate is limited, then there would be no effect on the rate of reaction.

Question 18

How does substrate concentration effect enzyme activity?

Answer 18

• The higher the substrate concentration, the faster the reaction - more substrate molecules = more successful collisions. This is only true up until a ‘saturation’ point though. After that there are so many substrate molecules that the enzymes have about as much as they can cope with. Therefore, adding more substrate has no effect on the rate of reaction at all.
• Substrate concentration decreases over time, so if no other variables are changed, the rate of reaction will decrease over time. This makes the initial rate of reaction the highest rate of reaction.

Question 19

During the amylase practical what are you measuring?

Answer 19

• The disappearance of the substrate rather than the appearance of the product - to compare the rate of reaction under different conditions.

Question 20

What solution is used to detect the presence of starch?

Answer 20

Potassium iodide and iodine.

Question 21

How can you time how long it takes for the starch to disappear?

Answer 21

• By regularly sampling the starch solution.
• You can then alter the conditions of the reaction and compare rates.

Question 22

What is the independent variable on the catalase practical?

Answer 22

• Temperature.

Question 23

What is the dependent variable on the catalase practical?

Answer 23

• Volume of oxygen produced.

Question 24

What are the control variables for the catalase practical?

Answer 24

• pH
• Enzyme concentration
• Substrate concentration

Question 25

What happens to the temperature when investigating substrate concentration?

Answer 25

Temperature remains the same but prepare boiling tubes with different concentrations of hydrogen peroxide.

Question 26

How do you investigate pH?

Answer 26

Add a buffer solution with a different pH in each tube.