Enzymes

Question 1

The scientists set up two experiments, C and L.

Experiment C used

• the enzyme
• different concentrations of ATP.

Experiment L used

• the enzyme
• different concentrations of ATP
• a sugar called lyxose.

Lyxose binds to the enzyme.

Suggest a reason for the difference in the results shown in the graph with and without lyxose.

the experiment with lxyose has a higher rate

Answer 1

Binding) alters the tertiary structure of the enzyme ;

Max 1

if lyxose acting as an inhibitor

OR if answer linked to lower rate of reaction

OR if lyxose used an energy source/respiratory substrate

2. (This causes) active site to change (shape);
3. (So) More (successful) E-S complexes form (per minute)

OR

E-S complexes form more quickly

OR

Further lowers activation energy;

Question 2

Formation of an enzyme-substrate complex increases the rate of reaction.

Explain how.

Answer 2

Reduces activation energy;

Accept ‘reduces Ea’.

2. Due to bending bonds

OR

Without enzyme, very few substrates have sufficient energy for reaction;

Accept ‘Due to stress/pressure/tension on bonds’ OR ‘Due to weakening bonds’.

Question 3

Many humans are unable to digest lactose. A scientist investigated the production of lactose-free milk. He produced gel beads containing the enzyme lactase and placed the beads in a column. He poured milk (Milk A) into the column and collected the milk (Milk B) after it had moved through the column over the beads. This is shown in the diagram below.

(a) Milk A contains no glucose. Milk B contains glucose. Explain why Milk B contains glucose.

(b)The enzyme was trapped within the gel beads. Suggest one advantage of trapping the enzyme within the gel beads.

(e)Galactose has a similar structure to part of the lactose molecule.

Explain how galactose inhibits lactase.

Answer 3

Lactase hydrolyses lactose in to glucose (and galactose);

1

(b) No lactase in the milk

OR

Enzyme can be reused.

(e) 1. Galactose is a competitive inhibitor / attaches to the active site (of lactase);

2. Fewer enzyme substrate complexes formed.

Question 4

The scientist varied the flow rate of the milk through the column. The effect of flow rate on the concentration of glucose in Milk B is shown in the table below.

Flow rate of milk through the column / cm3 minute−1

Concentration of glucose in Milk B / arbitrary units

50

45

100

6

(c) Explain the difference in the results in the table.

Answer 4

100 cm3 minute–1 is too fast to bind to active site / converse for 50 cm3 minute–1;

Question 5

Washing powders often contain enzymes from bacteria. These enzymes include proteases that hydrolyse proteins in clothing stains.

The graph shows the effect of temperature on a protease that could be used in washing powder.

Explain the shape of the curves at 50 °C and 60 °C.

__50 degrees and 60 are both past optimum 60 degrees in at 0 rate

Answer 5

Both denatured (by high temperature);

2. Denaturation faster at 60 °C due to more (kinetic) energy;
3. Breaks hydrogen / ionic bonds (between amino acids / R groups);
4. Change in shape of the active site / active site no longer complementary so fewer enzyme-substrate complexes formed / substrate does not fit

Question 6

Catalase is used in a number of industrial processes. It is normally obtained from a fungus called Aspergillus niger. Scientists produced a mutant strain of A. niger called K30. They wanted to know if this mutant strain produced more catalase than the normal strain of A. niger.

• The scientists grew samples of the normal strain of the fungus and of the K30 strain on jelly in separate Petri dishes. The jelly contained a blue substance which is turned colourless by catalase.
• They incubated the dishes for 3 days then measured the diameter of the colourless zone around the fungus.
• They calculated the ratio of the diameter of the colourless zone to the diameter of the fungus.

The diagram shows the dishes after incubation.

Normal
strain

K30 strain

(a) The scientists grew both strains of fungi on dishes kept at 30 °C. Keeping the dishes at a temperature of 15 °C would affect the results. Use your knowledge of kinetic energy to explain why.

Answer 6

Molecules move at slower speeds;

2 diffusion or

2. Decreases rate of diffusion;

4 enzymes.

OR

3. Molecules move at slower speed;
4. Fewer collisions between enzymes and substrates / fewer enzyme-substrate complexes formed;

Question 7

The scientists gave their results as ratios. Explain the advantage of giving the results of this investigation as a ratio

Answer 7

Allows comparison;
2. Different amounts of fungus added / fungus is different size at start

Question 8

The enzyme tyrosine kinase (TK) is found in human cells. TK can exist in a non-functional and a functional form. The functional form of TK is only produced when a phosphate group is added to TK.

This is shown in Figure 1.

Figure 1

(a) Addition of a phosphate group to the non-functional form of TK leads to production of the functional form of TK.

Answer 8

Phosphate) changes shape of TK / changes shape of enzyme /
changes the active site;

It = phosphate

Accept ‘alters’ for changes

Reject that phosphate is an inhibitor

Accept adding energy / affecting charged / affects polar groups (on amino acids)

2. Active site forms / becomes the right shape / can bind to substrate / complementary to substrate / E-S complex can form;

Question 9

Many of the substances causing the food stains are large, insoluble proteins.
Suggest how a biological washing powder removes this type of stain

Answer 9

Enzyme hydrolyses / breaks down protein to amino acids;

2. Products are soluble / can be washed away;

Question 10

Biological washing powders often contain a number of different enzymes. This enables them to remove a wider range of stains from clothes.
Explain why a number of enzymes are required to remove a wider range of stains.

Answer 10

Stains caused by different substances;

2. Enzymes are specific;
3. Active site specific to substrate / other substrates cannot fit active site

Question 11

The student concluded from her investigation that the optimum pH of amylase was pH8. Is this conclusion valid? Explain your answer.

Answer 11

Only 2 pHs studied / more pHs need to be tested

Question 12

Read the following passage.

Alzheimer’s disease leads to dementia. This involves small β-amyloid

proteins binding together to form structures called plaques in the brain.

Nerve cells in the brain produce a large protein called amyloid-precursor

protein that has a complex shape. This protein is the substrate of two

different enzymes, α-secretase and β-secretase. These enzymes are 5

normally produced in the brain. One product of the reaction catalysed by

β-secretase is a smaller protein that can lead to β-amyloid protein formation.

Many people with Alzheimer’s disease have mutations that decrease

α-secretase production, or increase β-secretase production.

One possible type of drug for treating Alzheimer’s disease is a competitive 10

inhibitor of β-secretase. When some of these types of drugs were trialled on

patients, the trials had to be stopped because some patients developed

serious side effects.

Use information from the passage and your own knowledge to answer the following questions.

(a) Suggest how amyloid-precursor protein can be the substrate of two different enzymes, α-secretase and β-secretase (lines 3–5).

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(2)

(b) One product of the reaction catalysed by β-secretase is a smaller protein (lines 6–7).

Describe what happens in the hydrolysis reaction that produces the smaller protein from amyloid-precursor protein.

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(2)

(c) Many people with Alzheimer’s disease have mutations that decrease α-secretase production, or increase β-secretase production (lines 8–9).

Use the information provided to explain how these mutations can lead to Alzheimer’s disease.

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(3)

(d) One possible type of drug for treating Alzheimer’s disease is a competitive inhibitor of β-secretase (lines 10–11).

Explain how this type of drug could prevent Alzheimer’s disease becoming worse.

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(2)

(e) When some of these types of drugs were trialled on patients, the trials were stopped because some patients developed serious side effects (lines 11–13).

Using the information provided, suggest why some patients developed serious side effects.

Answer 12

Mutations prevent production of enzyme(s)/functional enzyme;

2. (Increase in β-secretase) leads to faster/more β-amyloid production
   OR

(Decrease in α-secretase) leads to more substrate for β-secretase;

‘This’ must refer to α-secretase

3. (Leads to) more/greater plaque formation;

3

(d) 1. (Inhibitor) binds to/blocks active site of β-secretase/enzyme;

2. Stops/reduces production of β-amyloid/plaque;

2

(e) 1. Some β-amyloid required/needed (to prevent side effects)

OR

(Some) β-secretase needed;

Accept ‘Both enzymes needed’

2. Leads to build-up of amyloid-precursor protein (that causes harm)

OR

Too much product of α-secretase (causes harm);

Question 13

A student concluded from a graph of the data in the table that the bacterium lives at 15 °C.

Does the data support the student’s conclusion? Give reasons for your answer.

highest rate at 15 degrees values go in increment of 5 degrees

Answer 13

Expect optimum temperature of enzyme to be same

OR

Similar to temperature where bacterium lives;

2. Optimum temperature for enzyme (appears to be around) 15 °C;

No:

3. Need data from more temperatures (between 10 °C and 20 °C);
4. Data for only isolated enzyme