enz.test paper vsc 501

8/8/2019 Enz.test Paper VSC 501.

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Shri M. and N. Virani Science CollegeGyanyagna College of Science and Management

Semester 5 th Paper No. 501Unit Test

Total Marks: 50Section IQ.I Select the correct choice: [10 marks]1. If an enzyme solution is saturated with substrate, the most e ff ective way to obtain an

even f aster yield o f products is toa. add more o f the enzyme.

b. heat the solution to 90C.c. add more substrate.d. add an allosteric inhibitor.e. add a noncompetitive inhibitor.

2. If an enzyme has been inhibited noncompetitively,a. the G f or the reaction it catalyzes will always be negative.

b. the active site will be occupied by the inhibitor molecule.c. raising substrate concentration will increase the inhibition.d. more energy will be necessary to initiate the reaction.e. the inhibitor molecule may be chemically unrelated to the substrate.

3.A competitive inhibitor o f an enzyme is usually:a) a highly reactive compound.

b) a metal ion such as Hg 2+ or Pb 2+ .c) structurally similar to the substrate.d) water insoluble.e) a poison.

4. Which statement best expresses the in f ormation represented in the graph shown?

(1.) The action o f enzymes varies with pH . (2.) A pH o f 7 provides the optimumenvironment f or digestive enzymes (3.) Gastric juice is active at a pH extending f rom0 to 12. (4.) Acids have a pH greater than 7.

5. The steady state assumption, as applied to deriving the Michaelis-Mentena) Km=[S].


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b) The enzyme is regulated.c) The rate o f ES breakdown to EP is k 2.d) The ES complex is f ormed and broken down at equivalent rates.e) The maximum velocity occurs when the enzyme is saturated.

6. Which o

f these statements about enzyme-catalyzed reactions is fals e?a) At saturating levels o f substrate, the rate o f an enzyme-catalyzed reaction is

proportional to the enzyme concentration. b) If enough substrate is added, the normal V max o f a reaction can be attainedeven in the presence o f a competitive inhibitor.c) The rate o f a reaction decreases steadily with time as substrate is depleted.d) The activation energy f or the catalyzed reaction is the same as f or theuncatalyzed reaction.e) The Michaelis-Menten constant K m equals the [S] at which V = 1/2 V max.

7 . V max f or an enzyme-catalyzed reaction:

a) generally increases when pH increases. b) increases in the presence o f a competitive inhibitor.c) is limited only by the amount o f substrate supplied.d) is twice the rate observed when the concentration o f substrate is equal to the K m.e) is unchanged in the presence o f a uncompetitive inhibitor.

8. Which o f the f ollowing statements about enzymatic catalysis I S FALSE?a. A reaction may not occur at a detectable rate even though it has a

f avorable equilibrium b. The substrate binds to an enzyme active sitec. I ncreasing the temperature o f the reaction will increase the reaction rated. The equilibrium o f the reaction is shi f ted towards the f ormation o f the

product(s)e. All the above answers are CORRECT

9. Many enzymes require co f actors to f unction. Many o f these co f actors are vitamins.Which o f the f ollowing statements is NOT true?a) Fe, Zn, Cu, Mg, Mn, K, Ni, and Mo are classi f ied as vitamins.

b) Humans have lost the ability to synthesize vitamins..c) Vitamins are modi f ied by the body to f orm coenzymes..d) There are 2 classes o f vitamins: water-soluble and f at-soluble.

10. Allosteric enzymes are large, oligomeric proteins that have catalytic sites f or bindingsubstrates and regulatory sites that bind e ff ectors. The separate oligomers in f luence oneanother; they work cooperatively. This is evidenced by the characteristic rate curves f or allosteric enzymes which have:.a)Michaelis-Menten kinetics. b)Hyperbolic kinetics.c)Sigmoidal kineticsd)Regulatory kineticse)Concerted kinetics


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11. Match each of th e following s tructur es wi th th e c orr esponding n am e of th e c om pou nd:

1) 2) 3)

4) 5)

A) 1, FAD; B) 1, NAD +;2, NAD +; 2, Coenzyme A;3, Coenzyme A; 3, FAD;4, ATP; 4, ATP;5, Thiamine pyrophosphate. 5, Thiamine pyrophosphate.

C) 1, Coenzyme A; D) 1, NAD +;2, NAD +; 2, Coenzyme A;3, FAD; 3, FAD;4, Thiamine pyrophosphate. 4, Thiamine pyrophosphate;5, ATP. 5, ATP.

E) 1, FAD;2, Coenzyme A;3, NAD +;


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4, Thiamine pyrophosphate;5, ATP.

Q II Give answer in short: [2 marks x 5 =10]1. What is a biocatalyst?

2. What are the two main overall purposes of enzymes in our cells?

3. Why does an enzyme lose its activity when the pH not optimum?

4.. Which vitamin is used to make each of the following coenzymes?a) FAD b) NAD + c) CoA

5. Why during prolonged high fever a person will die? Give answer in relation to


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a) Role of enzyme in body, b) Effect of temperature on enzyme.

Q III . [5 marks]Two di ff erent enzymes are able to catalyze the same reaction, A B. They both have

the same V max , but di ff er their K m the substrate A. For enzyme 1, the K m is 1.0 mM; f or enzyme 2, the K m is 10 mM. When enzyme 1 was incubated with 0.1 mM A, it wasobserved that B was produced at a rate o f 0.0020 mmoles/minute.a) What is the value o f the V max o f the enzymes? (4 pts)

b) What will be the rate o f production o f B when enzyme 2 is incubated with 0.1 mM A?(2 pt)c) What will be the rate o f production o f B when enzyme 1 is incubated with 1 M A? (2

pts)[Hint: V 0 = V max [S]/( K m + [S])]

enz.test paper vsc 501

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