UNIT-1 Principles of catalysis, enzymes, and enzyme kinetics, enzyme regulation, mechanism enzyme catalysis, isozymes

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there are 25 question for practice of PAPER C OF EACH MARKS 2

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Enzyme & Metabolism

How many types of enzymatic regulation mechanism occurs in the cells?

2 points

a) 2

b) 3

c) 4

d) 5

Clear selection

Why does the rate of enzyme activity increase as this approaches 40?

2 points

there are more collisions between enzyme and substrate

there is more enzyme present

the enzyme is becoming denatured

because there is more kinetic energy

Clear selection

Which of the following is not an example of irreversible enzyme inhibitor?

2 points

a) Cyanide

b) Sarin

c) Diisopropyl phosphoflouridate (DIPF)

d) Statin drugs

Clear selection

Which of the following best describes the function of competitive inhibitors?

2 points

Increase the Vmax

Increase the Km

No change in Vmax

Decrease the Km

Increase in Vmax

Both b and c true

Clear selection

A non-competitive inhibitor of an enzyme-catalyzed reaction

2 points

binds to the Michaelis complex (ES).

decreases Vmax.

is without effect at saturating substrate concentrations.

can actually increase reaction velocity in rare cases.

The first and second choices are both correct.

Clear selection

Which of the following is an example of ligases enzyme?

2 points

a) Mutases

b) Epimerases

c) Racemases

d) Carboxylases

Clear selection

The degree of inhibition α by a competitive inhibitor is obtained from

2 points

measurement of Vmax.

measurement of the y-intercept on a Limeweaver-Burke Plot.

measurement of KM.

crystallographic studies.

is unrelated to the binding affinity of the inhibitor to the enzyme

Clear selection

What should be on the x axis?

2 points

enzyme concentration

enzyme concentration or substrate concentration

substrate concentration

Clear selection

2 points

Clear selection

Lineweaver-Burk plot is also known as______

2 points

a) Double reciprocal plot

b) Hanes-Woolf plot

c) Eadie-Hofstee plot

d) Steady-state equation

Clear selection

Applying the Michaelis-Menten Equation I A research group discovers a new version of happyase,which they call happyase*, that catalyzes the chemical reactionHAPPY88zy88 SADThe researchers begin to characterize the enzyme.(a) In the first experiment, with [Et] at 4 nM, they find that the Vmaxis 1.6 MICROMsPER SECOND. Based on this experiment, what is the kcatTimefor happyase*? (Include appropriate units.

2 points

200

400

600

800

Other:

Clear selection

A competitive inhibitor of an enzyme is usually:

2 points

a highly reactive compound.

a metal ion such as Hg2+ or Pb2+.

structurally similar to the substrate.

water insoluble.

a poison.

Clear selection

A competitive inhibitor has the following effect on a Limeweaver-Burke (double reciprocal) Plot

2 points

It moves the entire curve to the right.

It moves the entire curve to the left.

It changes the y-intercept.

It changes the x-intercept.

It hs no effect on the slope.

Clear selection

Which of the following is false?

2 points

a) Allosteric modulators may be inhibitory or stimulatory

b) Based on the nature of modulator, allosteric enzymes are of two types

c) Homotropic allosteric enzymes have the substrate and modulator same

d) Heterotropic allosteric enzymes have the substrate and modulator same

Clear selection

What is the ratio of Vo/Vmax when [S]=5KM ?

2 points

1/2

Cannot be determined

5/6

4/5

1/5

Clear selection

Phosphorylase a +2H2O → phosphorylase b + 2PiWhich of the following is false about this reaction?

2 points

a) Phosphorylase a is less active and phosphorylase b is more active

b) Glycogen phosphorylase catalyzes this reaction

c) Phosphorylase b can be transformed back into phosphorylase a by phosphorylase kinase

d) Phosphorylase kinase catalyzes the transfer of phosphoryl groups from ATP to Phosphorylase b

Clear selection

What is limiting the rate of reaction at point A?

2 points

SUBSTRATE concentration

enzyme concentration

substrate concentration or enzyme concentration

Clear selection

Which of the following is not a catalytic strategy for an enzyme to perform specific reaction?

2 points

a) Covalent catalysis

b) Metal ion catalysis

c) Michaelis constant

d) Acid-base catalysis

Clear selection

Put the enzymes of the last five steps of glycolysis in the correct order a. phosphogylcerate mutase b. enolate c. phosphoglycerate kinase d. glyceraldehyde 3-phosphate dehydrogenase e. pyruvate kinase

2 points

D,C,A,B,E

C,A,B,E,D

A,B,E.D,C

D,C,B,E,A

Clear selection

Carbon monoxide binds to hemoglobin at the same site as oxygen, and it does so with a much higher affinity - carboxyhemoglobin results. The type of inhibition by carbon monoxide on hemoglobin is which of the following?

2 points

Competitive inhibition

No inhibition

Noncompetitive inhibition

Uncompetitive inhibition

Mixed-inhibition

Clear selection

The diagram shows a metabolic pathway. What would happen to the rate of production of D if enzyme 1 was not present?

2 points

it would be increased

it would be reduced

it would stop

it wouldn't be any different

Clear selection

Which of the following is false about the Michaelis-Menten equation?

2 points

Velocity is proportional to substrate concentration.

Velocity is proportional to enzyme concentration.

Velocity is proportional to the turnover number.

The maximum rate of reaction is reached as the substrate concentration increases indefinitely.

Velocity is inversely proportional to enzyme concentration.

Clear selection

NMP kinase transfers a phosphoryl group from

2 points

ATP to NMP

ATP to AMP

ADP to AMP

Option 4

Other:

Clear selection

What is the SI unit of enzyme activity?

2 points

a) Km

b) Kat

c) Kcat

d) Vmax

Clear selection

EC number 1.1.1.27 is an

2 points

Oxidoreductase

TRANSFERASE

LYASE

LIGASE

Clear selection

What would happen to the rate of production of D if the concentration of enzyme 1 was increased but the concentration of enzymes 2 and 3 remained constant?

2 points

it would be increased

it would be reduced

it would stop

it wouldn't be any different

Clear selection

All of the following are properties of uncouplers except:

2 points

they dissipate the proton gradient.

they increase the ATP/ADP ratio.

they do not disruptthe electron transport mechanism.

they cause heat production

Clear selection

2 points

Clear selection

Place the following reaction intermediates of the citric acid cycle in chronological order (from the most reduced to the most oxidized form)a. malate b. fumarate c. succinyl CoA d. Citrate e. alpha-ketoglutarate

2 points

e,c,b,a,d

c,b,a,d,e

d,e,b,a,c

d,e,c,b,a

Clear selection

Which of the following is false?

2 points

a) Allosteric modulators may be inhibitory or stimulatory

b) Based on the nature of modulator, allosteric enzymes are of two types

c) Homotropic allosteric enzymes have the substrate and modulator same

d) Heterotropic allosteric enzymes have the substrate and modulator same

Clear selection

Which of the following will increase the reaction rate of an enzymatic reaction? I. Adding a competitive inhibitor II. Increasing the substrate concentration III. Decreasing the affinity of the substrate to the enzyme

2 points

I and III

I and II

II only

I only

Clear selection

Mark the CORRECT function of enzyme, endoPeptidase?

2 points

a) Cleave internal phosphodiester bond

b) Cleave PEPTIDE into amino bonds

c) Remove phosphate from a substrate

d) Removal of H2O

Clear selection

At saturating concentrations of substrate, a reaction catalyzed by an allosteric enzyme is (with respect to substrate)

2 points

(a) zero order

(b) first order

(d) third order

(e) mixed order

Clear selection

Which of the following is true regarding competitive inhibition?

2 points

It decreases the maximum effect of the enzyme only

It decreases the maximum effect of the enzyme and it decreases the attraction between enzyme and substrate

It decreases the attraction between enzyme and substrate only

None of these

Clear selection

An allosteric inhibitor of an enzyme usually

2 points

binds to the active site.

participates in feedback regulation.

denatures the enzyme.

causes the enzyme to work faster.

is a hydrophobic compound

Clear selection

During the intense exercise creatine kinase can be used to quickly regenerate ATP from ____

2 points

creatine phosphate

lactic acid

Malic acid

All

Clear selection

Protein kinases are enzymes that act on other enzymes by adding phosphates groups. When the enzyme is phosphorylated, it changes its activity (it becomes more or less active, depending on the enzyme). This regulatory mechanism of enzymatic activity is called

2 points

A) Allosteric Control

B) Competitive inhibition

C) Covalent Modification

D) Isozymes Modification

E) Zymogen activation

Clear selection

What is the function of phosphorylase?

2 points

a) Transfer inorganic phosphate

b) Transfer a carboxylate group

c) Use H2O2 as the electron acceptor

d) Transfer amino group

Clear selection

Why does the graph level off at point B?

2 points

because the enzyme is beginning to denature

because the enzyme has been used up

because another factor is limiting e.g. enzyme concentration

because there are not enough substrate molecules left

Clear selection

This graph is showing the effect of....

2 points

SUBSTRATE concentration

enzyme concentration

substrate concentration or enzyme concentration

Clear selection

There are at least four types of glucose transporter in the body. GLUT1 and GLUT3 are located in most tissues including the brain and the red blood cells. These glucose transporters rapidly take up glucose from the blood but have the lowest Vmax value. GLUT2 is commonly found in the liver and the pancreas. GLUT2 has a lower affinity for glucose but has the highest Vmax value. GLUT4 is common in skeletal tissues and in adipose tissues. This transporter is normally not active for uptake unless stimulated by insulin or during exercise. Suppose there is a molecule that is able to lower the Vmax of the enzyme. What type of regulation would this molecule exhibit?

2 points

Cooperative stimulation

Noncompetitive inhibition

Cooperative inhibition

Competitive inhibition

Uncompetitive stimulation

Clear selection

During the digestion process, complex carbohydrates are absorbed by the intestinal cells:

2 points

a. as acetyl CoA.

b. as starch or glycogen.

c. as they are converted to glucose and simple sugars.

d. as short four glucose residues.

Clear selection

Suppose that an enzyme mixture contains an enzyme with a michaelis constant of 5.0∗10−6M. If the substrate concentration in this mixture is 4.5∗10−6M, what is the fractional saturation of this enzyme mixture?

2 points

68.13%

26.31%

23.68%

47.37%

52.63%

Clear selection

Name the coenzyme of riboflavin (B2)?

2 points

a) NAD or NADP

b) FAD and FMN

c) Coenzyme A

d) Thiamine pyrophosphate

Clear selection

Which of the following best describes the function of competitive inhibitors?

2 points

Increase the Vmax

Increase the Km

No change in Vmax

Decrease the Km

Increase in Vmax

Both b and c true

Clear selection

Enzymes have a 3-D shape due to which type of protein structure?

2 points

primary structure

secondary structure

tertiary structure

quaternary structure

Clear selection

Mark the CORRECT function of enzyme, Peptidase?

2 points

a) Cleave phosphodiester bond

b) Cleave PEPTIDE into amino bonds

c) Remove phosphate from a substrate

d) Removal of H2O

Clear selection

Which of the following intracellular conditions lead to the release of insulin from the pancreatic B-cells?

0 points

High K+ and high Ca+

High Ca+ and Low K+

Low Na+ and high Ca+

High K+ and Low Na+

Clear selection

Which of the following is false about allosteric feedback inhibition?

2 points

a) Bacterial enzyme system is the first known example

b) Conversion of L-leucine to L-isoleucine

c) Threonine dehydratase is inhibited by isoleucine

d) If the isoleucine concentration decreases, the rate of threonine dehydration increases

Clear selection

Given an enzyme with KM of 0.5mM. at what substrate concentration will the velocity of the enzyme reach 1/4 of the Vmax? Vmax=200 mmols

2 points

0.12mM

0.20mM

0.5mM

0.17mM

Clear selection

A researcher adds 1M of competitive inhibitors to an existing solution of substrate and enzyme. The researcher notices that the effect of the enzyme decreases. What can the researcher do to increase the effect of the enzyme back to normal levels (to levels before inhibitors were added)?

2 points

Increase the volume of the solution

Nothing can be done to bring enzyme activity to normal levels

Increase the concentration of substrate

Decrease the volume of the solution

Clear selection

At what substrate concentration can you measure the quarter of the maximal velocity of the enzyme if KM = 5·10-3?

2 points

[S] = 1.67 mM

[S] = .067 mM

[S] = 1.07 mM

[S] = .67 mM

Clear selection

Name the enzyme which catalyzes the oxidation-reduction reaction?

2 points

a) Transaminase

b) Glutamine synthetase

c) Phosphofructokinase

d) Oxidoreductase

Clear selection

All of the following are substrates for gluconeogenesis except:

2 points

fatty acids

gylcerol

oxaloacetate

lactic acid

Clear selection

Increased release of the hormone glucagon results in all of the following except:

2 points

a. stimulation of gluconeogenesis

b. inhibition of glycolysis

c. phosphalation of PFK2

d. decreased levels of fructose 2,6-biphosphate (F-2,6-BP)

e. decreased binding of cAMP to protein kinase A

Clear selection

Pyruvate dehydrogenase phosphate deficiency results in which condition?

2 points

high blood levels of lactic acid

high blood levels of glucose

high blood levels of pyruvic acid

high blood levels of malic acid

Other:

Clear selection

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