3. H2 Enzymes Questions

Anglo-Chinese Junior College Revision Package H2 & H1 Biology Enzymes

Multiple Choice Questions

1. Enzyme molecules with high optimum temperature will have

A less associated non-protein groups.

B less hydrophobic amino acid residues.

C more cysteine residues in their polypeptide chains.

D more peptide bonds than other enzyme molecules.

2. In an investigation to determine the effect of temperature on the activity of an enzyme, the time taken for all the substrates to disappear from a standard solution was recorded.

Which graph shows the result of this investigation?

A

B

C

D

3. The diagram below shows a simple metabolic pathway.

Which response shows feedback inhibition?

Metabolite Binding site of metabolite

A F Active site of enzyme 1

B F Allosteric site of enzyme 1

C I Active site of enzyme 1

D I Allosteric site of enzyme 1

F G H I

Enzyme 1 Enzyme 2 Enzyme 3


4. The graph shows the results of an experiment in which samples containing the same

concentration of enzyme and substrate were kept at different temperatures for periods of

one, two and five hours. The quantities of product formed were then determined.

Which of the following options best explains why the optimum temperature is lower if the

quantity of product formed is measured after five hours rather than one hour?

A Tertiary bonds are not broken at higher temperatures.

B The enzyme has a range of optimum temperatures.

C A longer time at high temperature denatures enzyme.

D The optimum temperature for the enzymes is 45C.


5. The diagram shows an enzyme molecule with its normal substrate and products. P and

Q are other molecules that can bind to the enzyme.

The graph shows the effect of P and Q on the rate of reaction of the enzyme at different

substrate concentrations.

Which statement correctly describes the activity of the enzyme?

A P is a competitive inhibitor which binds to the active site, resulting in curve R.

B P is a non-competitive inhibitor which distorts the shape of the enzyme, resulting in

curve S.

C Q is a competitive inhibitor which distorts the shape of the enzyme, resulting in

curve R.

D Q is a non-competitive inhibitor which binds to the active site, resulting in curve S.


6. The monomers of both starch and cellulose are glucose molecules. Which of the

following best explains why amylase can only break down starch but not cellulose?

A The large number of cross-linkages between adjacent cellulose molecules that

prevents amylase from breaking down cellulose.

B Amylase can only recognize -glycosidic linkages, which are present in starch but

not cellulose.

C The glycosidic bonds between the monomers in cellulose are stronger than in

starch.

D Cellulose is too large to be broken down by amylase.

7. Catalase is an enzyme that breaks down hydrogen peroxide. A scientist discovered a

new substance X, which will decrease the rate of enzymatic reaction of catalase when

added into the system. The addition of substrate, however, will increase the rate of

reaction again.

From the information given above, what can you conclude about substance X?

A It has similar molecular configuration to hydrogen peroxide.

B It binds to a site away from the active site of the catalase enzyme.

C It has the same configuration as the active site of catalase.

D It increases the pH of the system.

8. The four unknown substances shown below form part of an enzyme-catalysed pathway.

The addition of substance V results in no change in the concentration of W, and an

accumulation of X, and a near absence of both Y and Z. Further addition of Y results in

the formation of Z.

What does this information indicate about substance V?

A It is an inhibitor of enzyme 1

B It is an inhibitor of enzyme 2

C It is an inhibitor of enzyme 3

D It catalyses the formation of X


9. Which of the following statements about the function of enzymes is correct?

A Enzymes can speed up reaction but they cannot change the net energy output as

the activation energy cannot be changed.

B Enzymes can speed up the reaction by increasing the activation energy of a

reaction.

C Enzymes lower the activation energy of a reaction and change the net energy

output.

D Enzymes lower the activation energy of a reaction but do not change the net energy

output..

10. In an experiment using starch and amylase, the concentrations of starch and maltose

present in the reacting mixture are measured every minute for 20 minutes. 1%

hydrochloric acid is added after 10 minutes and the mixture is heated to 60C at 14

minutes.

Which graph represents the results of this experiment? C


11. The diagram shows a metabolic pathway controlled by end product inhibition. As the

concentration of the end product increases above the set level, an enzyme in the

pathway leading to the end product is inhibited.

An increase in the concentration of end product 6 does not lead to a decrease in the

synthesis of end product 9.

Which enzyme is inhibited by end product 6?

A Metabolite 1 Metabolite 2

B Metabolite 2 Metabolite 3

C Metabolite 3 Metabolite 4

D Metabolite 3 Metabolite 7


12. Lactose is a disaccharide present in milk. The enzyme -galactosidase catalyses the

breakdown of lactose to glucose and galactose.

10 cm3 of a 1% -galactosidase solution was added to 10 cm3 of milk. The graph shows

the total amount of glucose produced over the next ten minutes.

Then, 10 cm3 of a 2% galactosidase solution was added to 10 cm3 of milk.

Which graph shows the expected results?


13. An enzyme is a globular protein held together by several different types of chemical

bond, giving the enzyme primary, secondary and tertiary levels of structure. Which

correctly summarises the types of bond involved in each level of structure?

Disulfide Bonds Hydrogen Bonds Ionic Bonds Peptide Bonds

A Tertiary Secondary, Tertiary Tertiary Primary

B Primary, Tertiary Primary Secondary, Tertiary Secondary

C Secondary Secondary Tertiary Primary

D Primary Tertiary Secondary Tertiary

14. Indinavir is a commercial HIV-1 protease inhibitor administered by doctors to treat AIDS

patients. It is supposed to act as a competitive inhibitor.

Which of the following shows the correct combination of the Km value and maximum

velocity (Vmax) of HIV-1 protease when Indinavir is added together with its substrate?

Km Maximum velocity (Vmax)

A Remains the same Increases

B Remains the same Decreases

C Increases Remains the same

D Decreases Decreases

15. The figure shows a series of reactions in a metabolic pathway.

Enzyme 3 catalyses the splitting of C into D and J. Assuming that product E is an

allosteric inhibitor of 3, which of the following would likely happen if E were not consumed

in a subsequent reaction?

A The rate of production of D would increase.

B The rate of production of E would remain the same.

C The rate of production of L would remain the same.

D The rate of production of all products D, E, J and K would decrease.

A 1

B 2

C 3

D 4

J 5

K 6

L

E


16. Substance X (a mineral ion) is actively transported into cells. Equal-sized samples of cells were placed in media containing different concentrations of X for an hour. The intracellular concentration of X was then measured. All other metabolic conditions were maintained at the optimum level. The graph below shows the results.

From the information given above, which one of the following would account for the level

region of the graph labelled Y?

A A respiratory inhibitor had been introduced.

B All the active transport carriers had been operating at their maximum rate.

C The active transport carriers had been inactivated by a non-competitive inhibitor.

D As the internal concentration of X rose, more of the substance X was metabolised.

17. In the following branched metabolic pathway, a dotted arrow with a minus sign symbolizes inhibition of a metabolic step by an end product:

Which reaction would prevail if both Q and S were present in the cell in high

concentrations?

A L M

B M O

C L N

D R S


18. When investigating enzyme/substrate interactions, which one of the following would be

expected to show a linear relationship under constant conditions?

A Amount of product against time, with the amount of substrate limited.

B Rate of reaction against substrate concentration, with the amount of enzyme

limited.

C Rate of reaction against enzyme concentration, in the presence of excess

substrate.

D Rate of reaction against enzyme concentration, with the amount of substrate

limited.

19. In the production of isoleucine from threonine in bacteria (Biochemical Pathway 1 [BP

1]), the end product acts as an inhibitor of the first enzyme in the pathway. In the

production of arginine (Biochemical Pathway 2[BP 2]), the end product has no influence

on other enzymes in the pathway. It is reasonable to conclude that in

A BP 1, if the production of enzyme 3 stops there would be continuous production of

isoleucine.

B BP 2, if the production of enzyme 3 stops there would be continuous production of

arginine.

C BP 1, providing all enzymes are present, the production of isoleucine would be

continuous if there was a continuous supply of threonine.

D BP 2, providing all enzymes are present, the production of arginine would be

continuous if there was a continuous supply of substrate.


20. The graph shows the amount of product formed by a standard concentration of enzyme

and a standard concentration of substrate at a temperature of 15 C.

Which graph shows the effect on the activity of the enzyme of increasing the temperature

to 20 C?


Structured Questions

1 Lysozyme is an enzyme found in many places within the human body. It consists of a single

polypeptide folded into a complex shape. Fig. 1.1 shows a ribbon model of lysozyme.

Fig. 1.1

(a) With reference to Fig. 1.1, describe region X. [2]

Lysozyme is one of the many hydrolytic enzymes found within a lysosome. The lysosome enzymes

are only active over a narrow range of pH, with an optimum of pH 5. The pH of the cytoplasm is 7.2.

The internal pH of lysosomes is maintained by actively concentrating H+ ions in the lysosome using

proton pumps.

(b) Describe how H+ ions could be moved across the lysosome membrane. [3]


(c) Explain why enzymes from a leaky damaged lysosome may not destroy the cell contents. [2]

(d) Suggest why the lysosome membrane is not destroyed by the enzymes in the lysosome. [2]

[Total: 9 marks]

2 Detergent is a mixture that is used for cleaning purposes. Some of the components present in the

detergent include enzymes, preservatives, pH buffers, water softener and oxidizers.

(a) Suggest one enzyme that may be found in detergent and state its possible function. [1]

(b) (i) Suggest a reason why pH buffers are found in detergent. [1]

(ii) Explain what will happen if the pH deviates from the optimum pH for enzyme activity.[3]


(c) Explain why laundry should not be washed with ice-cold water. [3]

(d) Explain how the structure of the enzymes in the detergent is stabilized [2].

[Total: 10 marks]

3 Fig. 4.1 below shows a model of the enzyme chymotrypsin. Chymotrypsin catalyses the hydrolysis

of peptide bonds of proteins. The active site of chymotrypsin is located in a slight depression on

one side of the molecule. Three amino acids form the active site. These three amino acids are

some distance apart on the polypeptide chain but close together in the active site.

Fig. 4.1


(a) Describe how amino acid residues at different positions in the protein may be brought together

in the active site when the enzyme is synthesised. [2]

(b) Explain how a substrate may be attached to the enzyme. [3]


Fig. 4.2 shows the effects of increasing substrate concentration on the rate of an enzyme-catalysed

reaction at a temperature of 35C and a constant pH.

Fig. 4.2

(c) With reference to Fig. 4.2, explain why an increase in substrate concentration at low substrate

concentrations increases the rate of reaction but an increase at high substrate concentrations

does not have the same effect. [4]

[Total: 9 marks]

Graph 3

Graph 2 Graph 1


4 Enzymatic browning is one of the most important colour reactions that affect fruits. Cut apples

turned brown after exposure to air within minutes. This browning reaction is catalysed by the

enzyme polyphenol oxidase (PPO), which is abundant in the flesh of the apples. PPO converts iron-

containing phenol compounds in the presence of oxygen to melanin in a series of polymerization

reactions. Fig. 5.1 shows the structure of the PPO enzyme.

Fig. 5.1

(a) With reference to Fig. 5.1, describe the structure of the PPO enzyme. [3]


(b) Suggest the role of PPO in melanin synthesis in apples. [2]

Fig. 5.2 shows the results of tests to determine the optimum temperature for the activity of PPO.

Percentage of

phenols

converted into

melanin in 10

minutes / %

Fig. 5.2

(c) With reference to Fig. 5.2,

(i) state the optimum pH and temperature for the enzyme PPO. [1]

pH: Temperature:

(ii) account for the curve at pH 8. [4]

[Total: 10 marks]


Essays

1 (a) Describe the roles of enzymes in DNA replication (KIV for DNA & Genomics) [8] (b) Explain the effect of a competitive inhibitor on the rate of enzyme activity. [4] 2 (a) Describe the effects of pH and temperature on enzyme-catalyzed reactions. [8] (b) Distinguish between competitive and non-competitive inhibition of enzyme action. [7] (c) Explain the effect of enzyme and substrate concentration on the rate of enzyme catalyzed

reactions. [5]

3. H2 Enzymes Questions

Documents

enzyme molecules

concentration of enzyme

f active site of enzyme

b f allosteric site

d cellulose

f g h i enzyme

b amylase

adjacent cellulose molecules