enzyme application

Question 1

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

Explain how galactose inhibits lactase.

Answer 1

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

2. Fewer enzyme substrate complexes formed.

Question 2

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

Answer 2

100 cm3 minute–1 is too fast to bind to active site

Question 3

Aspirin only affects one of the enzymes in this pathway. Use information in lines 5 - 7 to explain why aspirin does not affect the other enzymes.

Answer 3

Affects one monomer / amino acid;

i.e. What is affected

2. Not found in all active sites;

Question 5

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

Explain how.

Answer 5

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

It = phosphate

Accept ‘alters’ for changes

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 6

he binding of the functional form of TK to its substrate leads to cell division. Chronic myeloid leukaemia is a cancer caused by a faulty form of TK. Cancer involves uncontrolled cell division.

Figure 2 shows the faulty form of TK.

Figure 2 the functional group doesn’t have phosphate

Suggest how faulty TK leads to chronic myeloid leukaemia.

Answer 6

Faulty TK has functional active site without phosphate;

Accept ‘works without phosphate’

2. (So, faulty) TK functional all the time / TK not controlled (by phosphate);

Question 7

Attaching lactase to the beads is a more efficient use of lactase than adding the lactase directly to cow’s milk.

Suggest three reasons why it is more efficient to attach lactase to the beads.

Answer 7

(Lactase / beads) can be reused / not washed away;

1. Accept lactase / beads not wasted
2. Less lactase used is insufficient
3. No need to remove from milk;
4. Accept lactase not present in milk.
5. Allows continuous process;
6. The enzyme is more stable;
7. Avoid end-product inhibition.

Question 8

Monosaccharides and disaccharides taste sweet.
The lactose-free milk made after hydrolysis with lactase tastes sweeter than the cow’s milk containing lactose.
Suggest why.

Answer 8

Lactose hydrolysed to) galactose and glucose;

2. (So) more sugar molecules;
3. Idea of more sugars essential
4. (So) more / different receptors stimulated / sugars produced are sweeter (than lactose).

Question 9

Cyanide is poisonous. Cyanide binds to cytochrome oxidase, which is an enzyme in the electron transport chain in mitochondria. This stops the movement of electrons to oxygen. As a result, ATP cannot be made via aerobic respiration. If a person or animal is exposed to cyanide, a substance that acts as an antidote can reduce or prevent poisoning. This substance binds to cyanide.

Suggest how binding of cyanide to cytochrome oxidase affects the enzyme.

Answer 9

Inhibition;

Accept either competitive or non-competitive inhibition or a description of either.

2. Changes tertiary structure (of enzyme);
3. Changes shape of / blocks active site (of enzyme);

The active site must be in the context of the enzyme / cytochrome oxidase.

4. Enzyme cannot bind to its substrate / no enzyme-substrate
   complex formed.

Question 10

Suggest how amyloid-precursor protein can be the substrate of two different enzymes, α-secretase and β-secretase

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.( causes plaque

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.

Answer 10

(a) 1. Different parts/areas/amino acid sequences (of amyloid-precursor) protein;

Accept APP

2. Each enzyme is specific/fits/binds/complementary to a different part of the APP;

Point 2 subsumes point 1 and is worth 2 marks total.

2

(b) 1. Peptide bond broken;

2. Using water;

Hydrolysis in stem

(c) 1. 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;

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

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

if u want to go back number 13

Question 11

Amylase and maltase are involved in the digestion of starch in the small intestine.

Complete the table by identifying where these enzymes are produced and the product of the reaction they catalyse.

Name of enzyme

Where the enzyme is
produced

Product of the
reaction catalysed
by the enzyme

Amylase

Maltase

Answer 11

(Amylase) pancreas, produces maltose;

Place and product = 1 mark

(mark horizontally)

2. (Maltase) in / on epithelium (of small intestine), produces glucose;

Ignore references to salivary glands or saliva

Accept wall / lining of small intestine

Ignore reference to cells alone