Category: Biochemistry Objective Questions

250+ TOP MCQs on Regulatory Enzymes and Answers

Biochemistry Multiple Choice Questions on “Regulatory Enzymes”.

1. The allosteric inhibitor of an enzyme ___________
A. Causes the enzyme to work faster
B. Binds to the active site
C. Participates in feedback regulation
D. Denatures the enzyme
Answer: C
Clarification: In feedback regulation, enzyme is not directly inhibited by the end product instead its synthesis is inhibited by interfering with the gene of that enzyme.

2. Which of the following is false about allosteric feedback inhibition?
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
Answer: B
Clarification: The bacterial enzyme system that catalyses L-threonine to L-isoleucine are the first known example of allosteric feedback inhibition.

3. Which of the following is false?
A. Methyl, phosphoryl, adenyl, uridylyl and adenosine diphosphate ribosyl groups are the modifying groups
B. An example of an enzyme regulated by methylation is the methyl-donating chemo taxis protein of bacteria
C. The protein is a part of the system that permits a bacterium to swim towards attractant
D. The methylating agent is S- adenosylmethionine
Answer: B
Clarification: An example of an enzyme regulated by methylation is the methyl-accepting chemo taxis protein of bacteria.

4. Which of the following enzyme is responsible for the regulation of biological nitrogen fixation?
A. Dinitrogenase reductase
B. Dinitrogenase oxidase
C. Phosphatase
D. Kinase
Answer: A
Clarification: The bacterial enzyme, dinitrogenase reductase is responsible for the regulation of biological nitrogen fixation.

5. Which of the following enzymes catalyze the ADP-ribosylation of key cellular enzymes or proteins?
A. Diphteria toxin and cholera toxin
B. Dinitrogenase reductase
C. Protein phosphatases
D. Kinase
Answer: A
Clarification: The enzymes that catalyse the ADP-ribosylation and inactivation of key cellular enzymes or proteins are diphteria toxin and cholera toxin.

6. Removal of phosphoryl groups is catalyzed by ___________
A. Diphteria toxin and cholera toxin
B. Dinitrogenase reductase
C. Protein phosphatases
D. Protein kinases
Answer: C
Clarification: The enzymes that catalyze the ADP-ribosylation and inactivation of key cellular enzymes or proteins are diphteria toxin and cholera toxin. Dinitrogenase reductase is responsible for the regulation of biological nitrogen fixation. The attachment of phosphoryl groups to specific amino acid residues is catalyzed by protein kinases.

7. The attachment of phosphoryl groups to specific amino acid residues is catalyzed by ___________
A. Diphteria toxin and cholera toxin
B. Dinitrogenase reductase
C. Protein phosphatases
D. Protein kinases
Answer: D
Clarification: The enzymes that catalyse the ADP-ribosylation and inactivation of key cellular enzymes or proteins are diphteria toxin and cholera toxin. Dinitrogenase reductase is responsible for the regulation of biological nitrogen fixation. Removal of phosphoryl groups is catalyzed by Protein phosphatases.

8. Which of the following is false about the following reaction?

Phosphorylase a + 2H2O → phosphorylase b + 2Pi

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
Answer: A
Clarification: Phosphorylase is more active and phosphorylase b is less active.

9. Which of the following takes place due to phosphorylation of isocitrate dehydrogenase?
A. Inhibits the binding of citrate at active site
B. Degrades the enzyme
C. Enhances the substrate-binding affinity
D. No reaction
Answer: A
Clarification: The electrostatic repulsion by the phosphoryl group inhibits the binding of citrate at active site.

10. Which of the following enzyme catalyzes a reaction that introduces reduced nitrogen ito cellular metabolism?
A. Bacterial glutamine synthase
B. Bacterial dinitrogenase reductase
C. Bacterial dinitrogenase oxidase
D. Phosphatase
Answer: A
Clarification: Bacterial glutamine synthase is one among the most complex regulatory enzymes known. It catalyzes a reaction that introduces reduced nitrogen into cellular metabolism.

11. Which of the following is false about feedback regulation?
A. It is a type of enzymatic activity regulation
B. The synthesis of concerned enzyme is inhibited by interfering with the gene of that enzyme
C. Concentration of enzyme is reduced by the end product
D. The best example is the biosynthesis of L-isoleucine from L-threonine in bacteria
Answer: D
Clarification: The best example is reduction of HMG CoA reductase enzyme by dietary cholesterol.

12. Which of the following is false?
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
Answer: D
Clarification: In case of heterotropic enzymes both substrate and modulator are different.

13. In the case of allosteric enzymes what is the graphical representation when initial velocity is plotted against substrate concentration?
A. Straight line with negative slope
B. Hyperbola
C. Sigmoid curve
D. Parabola
Answer: C
Clarification: Allosteric enzymes do not obey Michaelis-Menten kinetics. So the curve is not hyperbolic.

14. How many types of enzymatic regulation mechanism occurs in the cells?
A. 2
B. 3
C. 4
D. 5
Answer: D
Clarification: Feedback inhibition, reversible covalent modification of enzymes, proteolytic activation of the enzyme, feedback regulation and regulation of isozymes.

15. Which is the enzyme that acts as a regulatory enzyme in a four-step metabolic pathway?
A. First enzyme
B. Fourth enzyme
C. Second enzyme
D. Third enzyme
Answer: A
Clarification: First reaction is the best place to regulate a metabolic pathway. So, the first enzyme acts as the regulatory enzyme.

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250+ TOP MCQs on Ionization of Water, Weak acids and Weak Bases and Answers

Biochemistry Interview Questions and Answers focuses on “Ionization of Water, Weak acids and Weak Bases”.

1. What is the concentration of OH– in a solution with a H+ concentration of 1.3×10-4 M?
A. 7.7×10-10 M
B. 7.7×10-9 M
C. 7.7×10-11 M
D. 7.7×10-12 M
Answer: C
Clarification: Kw = [H+][OH–]
Solving for [OH–] gives

[OH–]=(Kw)/([H+]) = (1.0 X 10-14)/(1.3 X 10-4) M
= 7.7 × 10-11 M.

2. Identify the triprotic acid from the following.
A. Carbonic acid
B. Bicarbonate
C. Glycine
D. Phosphoric acid
Answer: D
Clarification: Phosphoric acid is triprotic as it can give up three protons

3. Which of the following acids has the lowest pKa value?
A. Acetic acid
B. Sulphuric acid
C. Dil.HCl
D. Oxalic acid
Answer: B
Clarification: The stronger the acid, the lower its pKa. Sulphuric acid is the strongest acid of all the other acids mentioned, so its pKa is the least.

4. Which of the following bases has the highest pKa value?
A. NaOH
B. NaNO3
C. KNO3
D. KCl
Answer: A
Clarification: The stronger the base, the higher its pKa. NaOH is the strongest base of all the other bases mentioned, so its pKa is the highest.

5. The degree of ionization does not depend on?
A. Temperature
B. Current
C. Nature of solvent
D. Concentration
Answer: B
Clarification: Degree of ionization is independent of current. It depends only on temperature, nature of solvent and concentration.

6. The hydrolysis constant of CH3COONa is given by ____________
A. Kh = Kw/Ka
B. Kh = Kw/Kb
C. Kh = Kw/Ka×Kb
D. Kh = Ka + Kb
Answer: A
Clarification: CH3COONa is a salt of weak acid and strong base.

7. K1 and K2 for oxalic acid are 6.5×10-2and 6.1×10-5respectively. What will be the [OH–] in a 0.01M solution of sodium oxalate?
A. 9.6×10-6
B. 1.4×10-1
C. 1.2×10-6
D. 1.3×10-8
Answer: C
Clarification: The hydrolysis of C2 O42- is as follows
C2 O42-+ H2 O → HC2O4- + OH–

8. If pKb for fluoride at 25°c is 10.83, the ionization constant of hydrofluoric acid in water at this temperature is?
A. 3.52×10-3
B. 6.75×10-4
C. 5.38×10-2
D. 1.74×10-5
Answer: B
Clarification: Kw = Ka × Kb
Ka = Kw / Kb
Ka = 10-14/-log (10.83) = 6.75 × 10-4.

9. Aqueous solution of the detergents are _________
A. Neutral
B. Acidic
C. Basic
D. Amphoteric
Answer: C
Clarification: Detergent is a salt of weak acid and strong base.

10. If pH of solution of NaOH is 12.0 the pH of H2 SO4 solution of same molarity will be?
A. 2.0
B. 12.0
C. 1.7
D. 10.0387
Answer: C
Clarification: pH = 12 then pOH = 2
[OH–] = 10-2
Molarity of NaOH = 10-2
For H2 SO4, molarity = 10-2
[H+] = 2 × 10-2
pH = 2 – log2 = 1.7.

of Biochemistry for Interviews, .

250+ TOP MCQs on ATP Synthesis – 2 and Answers

Biochemistry online test on “ATP Synthesis – 2”.

1. The proposal of the chemiosmotic hypothesis was by ____________
A. Peter D. Mitchell
B. Charles Darwin
C. Mendele
D. Alfred Russell

Answer: A
Clarification: Peter D. Mitchell was the one to propose a chemiosmotic hypothesis.

2. ATP synthesis by chemiosmosis is by ____________
A. ATP dehydrogenase
B. Gyrase
C. ATP synthase
D. Dehydrogenase

Answer: C
Clarification: ATP synthase synthesizes ATP by chemiosmosis.

3. The measure of potential energy stored as a combination of proton and voltage gradients across membrane is termed as ____________
A. Proton motive force
B. Electron motive force
C. Molecule motive force
D. Ion motive force

Answer: A
Clarification: The measure of potential energy stored as a combination of proton and voltage gradients across membrane is termed as proton motive force.

4. The transport of acyl co-A for oxidation using a shuttle involves the formation of the intermediate ____________
A. Acyl coenzyme A
B. 3 acetyl co-A
C. Acyl cartinine
D. None

Answer: C
Clarification: The intermediate acyl cartinine is formed in the transport of acyl co-A for oxidation using a shuttle.

5. Three identical β subunits of the F1 complex during ATP synthesis have ____________
A. Different affinities for ATP and ADP
B. Similar affinities for ADP and ATP
C. Different affinities for ADP but not ATP
D. Different affinities for ATP but not ADP

Answer: A
Clarification: The conformational differences among β subunits extend to differences in their ATP/ADP-binding sites.

6. The acyl co-A formed in the cytosol is transported to ____________
A. Mitochondrial matrix
B. Microsomes
C. ER
D. Remains in cytosol

Answer: A
Clarification: The acyl co-A formed in the cytosol is transported to mitochondrial matrix.

7. Every cycle of β-oxidation produces ____________
A. 1 FAD, 1 NAD+ and 2 CO2 molecules
B. 1 FADH2, 1 NADH and 1 acetyl co-A
C. 1 FADH2, 1 NAD+ and 1 acetyl co-A
D. 1 FAD, 1 NADH and 2 CO2 molecules

Answer: B
Clarification: Every cycle of β-oxidation produces 1 FADH2, 1 NADH and 1 acetyl co-A.

8. Membrane potential and the proton gradient ____________
A. Cancel one another when uncouplers are present
B. Reinforce one another when respiratory inhibitors are present
C. Are sufficient, separately to make ATP from ADP + Pi
D. Are required to make ATP

Answer: D
Clarification: Membrane potential and proton gradient are both required to make ATP.

9. Long-chain fatty acids are oxidized step-wise in one carbon unit starting from ____________
A. Carboxyl end
B. Aliphatic end
C. Carboxyl and Aliphatic end
D. None of the mentioned

Answer: A
Clarification: Long-chain fatty acids are oxidized step-wise in one carbon unit starting from carboxyl end.

10. Maximum energy per gram on oxidation is yielded from ____________
A. Starch
B. Fat
C. Glycogen
D. Protein

Answer: B
Clarification: Fat yields maximum energy per gram on oxidation.

250+ TOP MCQs on Phosphoryl Group Transfers and ATP and Answers

Biochemistry Multiple Choice Questions on “Phosphoryl Group Transfers and ATP”.

1. Anabolism and catabolism are chemically linked in the form of __________
A. ADP
B. ATP
C. Phosphodiester linkage
D. ASP
Answer: B
Clarification: Anabolism is an energy intake process where small molecules build upto large molecules whereas catabolism involves the release of energy where large molecules tear down to smaller molecules.

2. Which of the following statements is false about ATP hydrolysis?
A. It is highly exergonic
B. Activation energy is relatively high
C. ∆G‘°=-30.5kJ/mol
D. ∆G‘°=30.5kJ/mol
Answer: D
Clarification: ∆G‘° should be negative for an exergonic process.

3. An endergonic reaction ____________
A. Proceeds spontaneously
B. Does not require activation energy
C. Releases energy
D. Requires energy
Answer: D
Clarification: Endergonic reaction involves intake of energy.

4. An exergonic reaction ____________
A. Proceeds spontaneously
B. Does not require activation energy
C. Releases energy
D. Requires energy
Answer: C
Clarification: Exergonic reaction involves release of energy.

5. Phosphoryl groups are derivatives of ____________
A. Phosphorous acid
B. Phosphoric acid
C. Acetic acid
D. Citric acid
Answer: B
Clarification: Phosphoryl groups are derivatives of phosphoric acid.

6. Water does a nucleophilic attack on phosphate monoester by producing ____________
A. Phosphorous chloride
B. Phosphorous sulfide
C. Inorganic phosphate
D. Organic phosphate
Answer: C
Clarification: Inorganic phosphate is produced when a nucleophilic attack is done by water on phosphate monoester.

7. The phosphate groups used during glycolysis are ____________
A. Organic
B. Inorganic
C. Neutral
D. None
Answer: B
Clarification: Phosphorous can only be produced from inorganic phosphate.

8. Which of the following is false about acetyl-coA?
A. It is a thioester
B. It has a large, negative standard free energy of hydrolysis
C. It contains phosphorous atom in the position occupied by an oxygen atom in oxygen esters
D. It contains a sulfur atom in the position occupied by an oxygen tom in oxygen esters
Answer: C
Clarification: Acetyl-coA is a thioester containing phosphorous atom in the position occupied by an oxygen atom in oxygen esters.

9. Which is an example of chemical to osmotic energy conversion that occurs in living organisms?
A. ATP-driven muscle contraction
B. ATP-dependent photon emission in fireflies
C. light-induced electron flow in chloroplasts
D. ATP-driven active transport across a membrane
Answer: D
Clarification: ATP-driven muscle contraction is an example for chemical to mechanical energy conversion.
ATP-dependent photon emission in fireflies is an example for chemical to electromagnetic energy conversion.
Light-induced electron flow in chloroplasts is an example for electromagnetic to electrical energy conversion.

10. Which is an example of chemical to electromagnetic energy conversion that occurs in living organisms?
A. ATP-driven muscle contraction
B. ATP-dependent photon emission in fireflies
C. light-induced electron flow in chloroplasts
D. ATP-driven active transport across a membrane
Answer: B
Clarification: ATP-driven muscle contraction is an example for chemical to mechanical energy conversion.
Light-induced electron flow in chloroplasts is an example for electromagnetic to electrical energy conversion.
ATP-driven active transport across a membrane is an example for chemical to osmotic energy conversion.

11. Which is an example of chemical to mechanical energy conversion that occurs in living organisms?
A. ATP-driven muscle contraction
B. ATP-dependent photon emission in fireflies
C. light-induced electron flow in chloroplasts
D. ATP-driven active transport across a membrane
Answer: A
Clarification: ATP-dependent photon emission in fireflies is an example for chemical to electromagnetic energy conversion.
Light-induced electron flow in chloroplasts is an example for electromagnetic to electrical energy conversion.
ATP-driven active transport across a membrane is an example for chemical to osmotic energy conversion.

12. Which is an example of electromagnetic to electrical energy conversion that occurs in living organisms?
A. ATP-driven muscle contraction
B. ATP-dependent photon emission in fireflies
C. light-induced electron flow in chloroplasts
D. ATP-driven active transport across a membrane
Answer: C
Clarification: ATP-driven muscle contraction is an example for chemical to mechanical energy conversion.
ATP-dependent photon emission in fireflies is an example for chemical to electromagnetic energy conversion.
ATP-driven active transport across a membrane is an example for chemical to osmotic energy conversion.

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250+ TOP MCQs on Lipids as Signals, Cofactors, and Pigments and Answers

Biochemistry Multiple Choice Questions on “Lipids as Signals, Cofactors, and Pigments”.

1. Phosphorylation of phosphatidylinositol yields __________
A. Phosphatidylinositol 4, 5-biphosphate
B. Phosphatidylinositol 3, 5-biphosphate
C. Phosphatidylinositol 3, 4-biphosphate
D. Phosphatidylinositol 5, 6-biphosphate
Answer: A
Clarification: Phosphorylation of phosphatidylinositol yields phosphatidylinositol 4, 5-biphosphate.

2. Which of the following vitamin is derived from cholesterol?
A. A
B. B
C. C
D. D
Answer: D
Clarification: Vitamin-D is derived from cholesterol.

3. What leads to the activation of protein kinase C?
A. Release of intracellular Ca+2 + diacylglycerol
B. Release of intracellular Mg+ + diacylglycerol
C. Release of intracellular Ca+2 + glycerol
D. Release of intracellular Ca+2 + triacylglycerol
Answer: A
Clarification: Release of intracellular Ca+2 + diacylglycerol causes activation of protein kinase C.

4. Which of the following serves as a specific binding site for the proteins involved in membrane fusion during exocytosis?
A. Phosphatidylinositol
B. Phosphatidylinositol 4, 5-biphosphate
C. Phosphatidylinositol 3, 5-biphosphate
D. Phosphatidylinositol 3, 4-biphosphate
Answer: B
Clarification: Phosphatidylinositol 4, 5-biphosphate in the cytoplasmic face of plasma membranes serves as a specific binding site for certain cytoskeletal proteins and for some soluble proteins involved in membranes fusion during exocytosis.

5. Which of the following hormone is responsible for the activation of phospholipase C?
A. Serotonin
B. Cortisol
C. Vasopressin
D. Adrenaline
Answer: C
Clarification: Vasopressin, when it binds to the plasma membrane receptors on the epithelial cells of the renal collecting duct, a specific phospholipase C is activated.

6. An example of glycerophospholipid involved in cell signaling is __________
A. Cardiolipin
B. Phosphatidic acid
C. Phosphatidylcholine
D. Phosphatidylinositol
Answer: D
Clarification: Phosphatidylinositol is involved in cell signaling.

7. Which of the following type structure contains all the three glycosphingolipids?
A. B structure
B. A structure
C. O structure
D. AB structure
Answer: C
Clarification: Type O structure has all three glycosphingolipids.

8. The lipids with potent bio activities derived from isoprenoid precursors are common in __________
A. Vitamin A, K, ubiquinone and dolichol
B. Vitamin A, D, ubiquinone and dolichol
C. Vitamin A, B, D and K
D. Vitamin A, B, K and dolichol
Answer: A
Clarification: Vitamin A, K, ubiquinone and dolichol have in common the lipids with potent bio activities derived from isoprenoid precursors.

9. Which of the following vitamin is responsible for Ca+2 and phosphate metabolism?
A. A
B. K
C. E
D. D
Answer: D
Clarification: Vitamin A –vision
Vitamin K-blood clotting
Vitamin E-prevention of oxidative damage.

10. How many products are obtained by the hydrolysis of phosphatidylinositol by phospholipase C?
A. 1
B. 2
C. 3
D. 4
Answer: B
Clarification: Inositol 1, 4, 5-triphosphate and diacylglycerol are the two products obtained by the hydrolysis of phosphatidylinositol by phospholipase C.

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250+ TOP MCQs on Examples Of Enzymatic actions and Answers

Biochemistry Multiple Choice Questions on “Examples Of Enzymatic actions”.

1. By what factor chymotrypsin enhances the rate of peptide bond hydrolysis?
A. 107
B. 108
C. At least 109
D. 106
Answer: C
Clarification: Chymotrypsin enhances the rate of peptide bond hydrolysis by a factor of at least 109.

2. The active site of chymotrypsin consists of a catalytic triad of which of the following amino acid residues?
A. Serine, histidine and aspartate
B. Serine, histidine and glutamate
C. Threonine, histidine and aspartate
D. Methionine, histidine and aspartate
Answer: A
Clarification: Aspartate holds the histidine side chain in the correct direction to accept proton from serine.

3. Which of the following statements are true about the reactions at the active center of chymotrypsin?
A. The aspartate residue gives an electron to histidine
B. The aspartate residue gives a proton to histidine
C. The aspartate residue keeps the histidine in the correct direction
D. A proton moves from the aspartate to serine to histidine in the catalytic triad of chymotrypsin
Answer: C
Clarification: Aspartate residue accepts a proton from serine.

4. The polypeptide chains in chymotrypsin are linked by ___________
A. Hydrogen bonds
B. Ionic bonds
C. Disulfide bond
D. SH-SH bond
Answer: C
Clarification: The protein consists of three polypeptide chains linked by disulfide bonds.

5. Which of the following is false about chymotrypsin?
A. Hydrolytic cleavage of a peptide bond by chymotrypsin has two phases
B. It is activated in the presence of trypsin
C. It is synthesized in the thyroid gland
D. Polypeptide chains in chymotrypsin are linked by S-S bonds
Answer: C
Clarification: Chymotrypsin is synthesized in the pancreas.

6. Which of the following is true about the structure of hexokinase?
A. U-shaped
B. T-shaped
C. E-shaped
D. G-shaped
Answer: A
Clarification: Hexokinase has a U-shaped structure.

7. Which of the following is true?
A. Xylose is stereo chemically similar to glucose but one carbon shorter
B. Xylose binds to hexokinase in a position where it can be phosphorylated
C. Addition of xylose increases the rate of ATP hydrolysis
D. The binding of xylose is sufficient to induce a change in hexokinase to its active conformation
Answer: B
Clarification: Xylose binds to hexokinase at a position where it cannot be phosphorylated.

8. Which of the following catalyzes the reversible degradation of 2-phosphoglycerate to phosphoenolpyruvate?
A. Chymotrypsin
B. Hexokinase
C. Enolase
D. Trypsin
Answer: C
Clarification: Enolase catalyzes the reversible degradation of 2-phosphoglycerate to phosphoenolpyruvate.

9. Which of the following catalyzes the reversible reaction of β-D-Glucose to glucose 6-phosphate?
A. Chymotrypsin
B. Hexokinase
C. Enolase
D. Trypsin
Answer: B
Clarification: Hexokinase catalyzes the reversible reaction of β-D-Glucose to glucose 6-phosphate.

10. Which of the following is false about lysozyme?
A. It is an antibacterial agent found in tears and egg white
B. The substrate of lysozyme is peptidoglycan
C. Lysozyme cleaves (β1 → 4) glycosidic C-O bonds between two types of sugar residue in the molecule NAM and NAG
D. It is a bisubstrate enzyme
Answer: D
Clarification: Hexokinase is the bisubstrate enzyme.

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