Category: Biochemistry Objective Questions

Biochemistry Multiple Choice Questions on “Weak Interactions in Aqueous Systems”.

1. What makes water a liquid at room temperature?
A. Hydrogen bonds between water molecules
B. Covalent bonding
C. Noncovalent interactions
D. Van der Waals forces of attraction
Answer: A
Clarification: Hydrogen bonds between water molecules provide the cohesive forces that make water a liquid at room temperature.

2. ΔG is negative for which of the following processes?
A. Melting of ice and evaporation of water
B. Oxidation of nitrogen
C. Oxidation of gold
D. Burning of chlorine
Answer: A
Clarification: The Gibb’s free energy change (ΔG) must have a negative value for a process to occur spontaneously.
Melting of ice and evaporation of water are the two spontaneous processes at room temperature.

3. ΔH is positive for which of the following processes?
A. Oxidation of nitrogen
B. Melting of ice and evaporation of water
C. Oxidation of gold
D. Burning of chlorine
Answer: B
Clarification: Enthalpy change (ΔH) is positive for endothermic reactions, the reactions which involves absorption of energy.
Melting of ice and evaporation of water involves absorption of energy.

4. What is the factor that is responsible for salts like NaCl to dissolve in water easily?
A. Decrease in entropy
B. Increase in entropy
C. Increase in enthalpy
D. Decrease in enthalpy
Answer: B
Clarification: As a salt such as NaCl dissolves, the Na⁺ and Cl^– ions leaves the crystal lattice resulting in an increase in entropy(randomness) of the system which is largely responsible for the ease of dissolving salts such as NaCl in water.

5. What is the heat of vaporization of water?
A. 2260 J/g
B. 2260 kJ/g
C. 1260 J/g
D. 1260 kJ/g
Answer: A
Clarification: The amount of energy needed to change one gram of water to its vapor form at constant temperature is 2260 J/g.

6. The bond dissociation energy of hydrogen bonds in a water molecule is ______________
A. 470 kJ/mole
B. 470 J/mole
C. 23 kJ/mole
D. 23 J/mole
Answer: C
Clarification: The energy required to break the hydrogen bonds (H-H) in water molecule is 23 kJ/mole.

7. The bond dissociation energy of O-H bond in a water molecule is _____________
A. 23 kJ/mole
B. 470 kJ/mole
C. 470 J/mole
D. 23 J/mole
Answer: B
Clarification: The energy required to break O-H bond in a water molecule is more than that required for breaking hydrogen bond, which is 470 kJ/mole.

8. Which of the following is a hypertonic solution?
A. Oceans
B. Freshwater habitats
C. 0.45% sodium chloride
D. Red blood cells placed in fresh water
Answer: A
Clarification: The sea water or oceans are hypertonic to the extracellular fluid of many of the marine organisms. These marine organisms overcome the problem of hyper tonicity by expelling the salt water continuously.

9. Which of the following is a hypotonic solution?
A. 10% dextrose in water
B. 0.45% sodium chloride
C. 5% dextrose in 0.9% sodium chloride
D. Oceans
Answer: B
Clarification: 0.9% normal saline is isotonic and half of 0.9 = 0.45% makes the solution more diluted (contains more water), therefore the solution is hypotonic.

10. Which of the following is an isotonic solution?
A. 0.9% sodium chloride
B. 0.45% sodium chloride
C. Oceans
D. 10% dextrose in water
Answer: A
Clarification: The normal saline solution, 0.9% NaCl has the same salt concentration as the surrounding blood cells.

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Biochemistry Multiple Choice Questions on “ATP Synthesis-1”.

1. Which of the following is the prosthetic group of NADH dehydrogenase?
A. NADH
B. FAD
C. NADPH
D. FMN
Answer: D
Clarification: NADH initially binds to complex I and transfers two electrons to the flavin mononucleotide (FMN) prosthetic group of the enzyme creating FMNH₂.

2. Effect of valinomycin on oxidative phosphorylation does not involve _____________
A. pH gradient across the inner mitochondrial membrane decreases
B. Rate of flow of electrons increases
C. Rate of oxygen consumption increases
D. Net yield of ATP decreases
Answer: A
Clarification: pH gradient does not decrease.

3. If mitochondria were blocked at the site of NADH oxidation and were treated with succinate as substrate, what would the P : O ratio is?
A. Same as that normally produced by succinate
B. One more than normally produced by succinate
C. One less than normally produced by succinate
D. Zero
Answer: A
Clarification: If mitochondria were blocked at the site of NADH oxidation and were treated with succinate as substrate, the P : O ratio is the same as that normally produced by succinate.

4. If 2, 4-dinitrophenol is added to tightly coupled mitochondria that are actively oxidizing succinate ____________
A. Electron flow will continue but ATP synthesis will not occur
B. Electron flow will continue but ATP synthesis will be increased
C. Electron flow will cease but ATP synthesis will continue
D. Both electron flow and ATP synthesis will be ceased
Answer: A
Clarification: Electron transfer is catalyzed from succinate or NADH to O₂ but no ATP synthesis is coupled to this respiration.

5. If the oxidative phosphorylation was uncoupled in the mitochondria then there is a/an ____________
A. Decreased concentration of ADP in the mitochondria
B. Decreased oxidative rate
C. Increased inorganic phosphate in the mitochondria
D. Decreased production of heat
Answer: C
Clarification: If the oxidative phosphorylation was uncoupled in the mitochondria then there is an increased inorganic phosphate in the mitochondria.

6. If rotenone is added to the mitochondrial electron transport chain then ____________
A. Succinate oxidation remains normal
B. P: O ratio of NADH is reduced from 3:1 to 2:1
C. Oxidative phosphorylation is uncoupled at site I
D. Rate of NADH oxidation is diminished to two-thirds of its initial value
Answer: A
Clarification: If rotenone is added to the mitochondrial electron transport chain succinate oxidation remains normal.

7. Which of the following takes place in substrate level phosphorylation?
A. Oxidation of one molecule of substrate is linked to synthesis of more than one ATP molecule
B. High energy intermediate compounds cannot be isolated
C. Only mitochondrial reactions participate in ATP formation
D. Substrate reacts to form a product containing a high energy bond
Answer: D
Clarification: Substrate reacts to form a product containing a high energy bond.

8. Chemiosmotic hypothesis does not involve ____________
A. Only proton transport is strictly regulated, other positively charged ions can diffuse freely across the mitochondrial membrane
B. ATPase activity is reversible
C. Proton flow into the mitochondria depends on the presence of ADP and Pi
D. Electron transport by the respiratory chain pumps protons out of the mitochondria
Answer: A
Clarification: Not only proton transport but there is electron transport also.

9. Which one of the following is the one having highest redox potential?
A. Ubiquinone
B. O₂
C. FMN
D. NAD
Answer: B
Clarification: O₂ has the highest redox potential.

10. Which of the following accepts only one electron?
A. Cytochrome b
B. Coenzyme Q
C. FMN
D. FAD
Answer: A
Clarification: Cytochrome b accepts only one electron.

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Biochemistry Multiple Choice Questions on “Bioenergetics and Thermodynamics”.

1. If enthalpy change for a reaction is zero, then ∆G° equals to _____________
A. -T∆S°
B. T∆S°
C. -∆H°
D. lnk_eq
Answer: A
Clarification: From the equation, ∆G° = ∆H°-T∆S°
If ∆H° = 0 then ∆G° = -T∆S°.

2. ∆G° is defined as the ____________
A. Residual energy present in the reactants at equilibrium
B. Residual energy present in the products at equilibrium
C. Difference in the residual energy of reactants and products at equilibrium
D. Energy required in converting one mole of reactants to one mole of products
Answer: D
Clarification: ∆G° is defined as the energy required in converting one mole of reactants to one mole of products.

3. For a reaction if ∆G° is positive, then ____________
A. The products will be favored
B. The reactants will be favored
C. The concentration of the reactants and products will be equal
D. All of the reactant will be converted to products
Answer: B
Clarification: If ∆G° is negative, products are favored.

4. Unfolding of regular secondary protein structure causes ____________
A. Large decrease in the entropy of the protein
B. Little increase in the entropy of protein
C. No change in the entropy of the protein
D. Large increase in the entropy of the protein
Answer: D
Clarification: Entropy increases on a larger scale when unfolding of secondary protein structure takes place.

5. The study of energy relationships and conversions in biological systems is called as ____________
A. Biophysics
B. Biotechnology
C. Bioenergetics
D. Microbiology
Answer: C
Clarification: Bioenergetics is the study of energy relationships and conversions in biological systems.

6. The relationship between K^‘_eq and ∆G^‘° is?
A. ∆G^‘° = RTlnK^‘_eq
B. ∆G^‘° = -RTK^‘_eq
C. ∆G^‘° = RK^‘_eq
D. ∆G^‘° = -RK^‘_eq
Answer: B
Clarification: If the system is in equilibrium ∆G° = 0 and ∆G^‘° = -RTK^‘_eq is the correct relation between K^‘_eq and ∆G^‘°.

7. What does first law of thermodynamics state?
A. Energy can neither be destroyed nor created
B. Energy cannot be 100 percent efficiently transformed from one type to another
C. All living organisms are composed of cells
D. Input of heat energy increases the rate of movement of atoms and molecules
Answer: A
Clarification: First law of thermodynamics can also be termed as law of conservation of energy which states that energy can neither be destroyed nor created but can be transformed from one form of energy to another.

8. If ∆G^‘° of the reaction A → B is -40kJ/mol under standard conditions then the reaction ____________
A. Will never reach equilibrium
B. Will not occur spontaneously
C. Will proceed at a rapid rate
D. Will proceed from left to right spontaneously
Answer: D
Clarification: If ∆G^‘° < 0, reaction proceeds from left to right that means products are favored.

9. What is the relationship between ∆G and ∆G^‘°?
A. ∆G = ∆G^‘° + RTln([products]/[reactants])
B. ∆G = ∆G^‘° – RTln([products]/[reactants])
C. ∆G = ∆G^‘° + RTln([reactants]/[products])
D. ∆G = ∆G^‘° – RTln([reactants]/[products])
Answer: A
Clarification: ∆G = ∆G^‘° + RTln([products]/[reactants] ) is the correct relation between ∆G and ∆G^‘°.

10. Which of the following statements is false?
A. The reaction tends to go in the forward direction if ∆G is large and positive
B. The reaction tends to move in the backward direction if ∆G is large and negative
C. The system is at equilibrium if ∆G = 0
D. The reaction tends to move in the backward direction if ∆G is large and positive
Answer: D
Clarification: The reaction tends to move in the backward direction if ∆G is large and negative.

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Biochemistry Multiple Choice Questions on “Structural Lipids in Membranes”.

1. Out of the following, cholesterol does not serve as a precursor for which compounds?
A. Vitamin D
B. Sex hormones
C. Bile salts
D. Bile pigments
Answer: D
Clarification: Cholesterol serves as a precursor for the biosynthesis of steroid molecules, bile acids and vitamin D.

2. Which of the following is a sphingophospholipid?
A. Lecithin
B. Sphingomyelin
C. Plasmolegen
D. Cardiolipin
Answer: B
Clarification: Lecithin, plasmolegen and cardiolipin are glycerophospholipids.

3. Which of the following glycerophospholid acts as a lipotropic agent?
A. Cardiolipin
B. Phosphatidylserine
C. Phosphatidylinositol
D. Phosphatidylcholine
Answer: D
Clarification: Only phosphatidylcholine acts as a lipotropic agent.

4. Which of the following phospholipids is a component of inner mitochondrial membrane?
A. Plasmologen
B. Cephalin
C. Lecithin
D. Cardiolipin
Answer: D
Clarification: Cardiolipin is an essential component of inner mitochondrial membrane.

5. In which of the following glycerophospholipids two phosphatidic acids share single glycerol?
A. Cardiolipin
B. Phosphatidylserine
C. Phosphatidylinositol
D. Phosphatidylcholine
Answer: A
Clarification: In cardiolipin, two phosphatidic acids share single glycerol.

6. Platelet activating factor stimulates the release of which of the following compounds?
A. Vasopressin
B. Serotonin
C. Adrenaline
D. Cortisol
Answer: B
Clarification: Platelet activating factor stimulates the release of serotonin.

7. Which of the following group of membrane lipids predominate in plant cells?
A. Galactolipids
B. Sphingolipids
C. Glycerophospholipids
D. Archaebacterial ether lipids
Answer: A
Clarification: Galactolipids are the lipids predominant in the chloroplasts of plants.

8. Which of the following membrane lipids have a direct glycosidic linkage between the head-group sugar and the backbone glycerol?
A. Glycolipids
B. Phospholipids
C. Sphingolipids
D. Ether lipids
Answer: A
Clarification: Glycolipids have a direct glycosidic linkage between the head-group sugar and the backbone glycerol.

9. The backbone of phospholipids is __________
A. L-glycerol 1-phosphate
B. L-glycerol 3-phosphate
C. D-glycerol 3-phosphate
D. sn-glycerol 1-phosphate
Answer: B
Clarification: L-glycerol 3-phosphate or D-glycerol 1-phosphate or sn-glycerol 3-phosphate is the backbone of phospholipids.

10. What is the head-group alcohol in plasmolegen and platelet-activating factor?
A. Alkene
B. Choline
C. Alkane
D. Acetic acid
Answer: B
Clarification: Choline is the head-group alcohol in plasmolegen and platelet-activating factor.

11. Which of the following does not contain glycerol?
A. Glycerophospholipids
B. Galactolipids
C. Sphingolipids
D. Triacylglycerols
Answer: C
Clarification: Sphingolipids contain sphingosine instead of glycerol.

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Biochemistry Multiple Choice Questions on “Enzyme Kinetics as an Approach to Understanding Mechanism”.

1. Which of the following is true about Michaelis-Menten kinetics?
A. K_m, the Michaelis constant, is defined as that concentration of substrate at which enzyme is working at maximum velocity
B. It describes single substrate enzymes
C. K_m, the Michaelis constant is defined as the dissociation constant of the enzyme-substrate complex
D. It assumes covalent binding occurs between enzyme and substrate
Answer: B
Clarification: K_m is defined as the concentration of substrate at which enzyme is working at half of maximum velocity. It is also a measure of the affinity that the enzyme has for its substrate. Michaelis-Menten kinetics assumes non-covalent binding between enzyme and substrate.

2. When the velocity of enzyme activity is plotted against substrate concentration, which of the following is obtained?
A. Hyperbolic curve
B. Parabola
C. Straight line with positive slope
D. Straight line with negative slope
Answer: A
Clarification: At low substrate concentration, the rate of a reaction is determined by the rate of formation of an enzyme-substrate complex.

3. Which of the following is the correct Line weaver-Burk equation?
A. (frac{1}{V_0} = frac{K_m}{V_{max} [S]} + frac{1}{V_{max}} )
B. (frac{1}{V_{max}} = frac{K_m}{V_0 [S]} + frac{1}{V_0} )
C. (V_0 = frac{V_{max} [S]}{K_m+[S]} )
D. (V_{max} = frac{V_0⁡ [S]}{K_m+[S]} )
Answer: A
Explanation:
Line weaver-Burk equation: (frac{1}{V_0} = frac{K_m}{V_{max} [S]} + frac{1}{V_{max}} )
Michaelis-Menten equation: (V_0 = frac{V_{max} [S]}{K_m+[S]} )

4. Which of the following statements is true about competitive inhibitors?
A. It is a common type of irreversible inhibition
B. In the presence of a competitive inhibitor, the Michaelis-Menten equation becomes
(V_0 = frac{V_{max} [S]}{α K_m+[S]} )
C. The apparent K_m decreases in the presence of inhibitor by a factor α
D. The maximum velocity for the reaction decreases in the presence of a competitive inhibitor
Answer: B
Clarification: Competitive inhibition is a common type of reversible inhibition.
The apparent K_m increases in the presence of inhibitor by a factor α.
The maximum velocity for the reaction remains same in the presence of a competitive inhibitor.

5. Which of the following statements is true about uncompetitive inhibitors?
A. They bind covalently at a site distinct from the substrate active site
B. In the presence of a uncompetitive inhibitor, the Michaelis-Menten equation becomes
(V_0 = frac{V_{max} [S]}{K_m+α’ [S]} )
C. They increase the measured V_max⁡
D. Apparent K_m also increases
Answer: B
Clarification: They bind non-covalently at a site distinct from the substrate active site.
They decrease the measured V_max⁡ and also apparent K_m.

6. The rate determining step of Michaelis-Menten kinetics is __________
A. The complex dissociation step to produce products
B. The complex formation step
C. The product formation step
D. None of the mentioned
Answer: A
Clarification: The breakdown of ES complex is the rate determining step of Michaelis Menten kinetics.

7. The molecule which acts directly on an enzyme to lower its catalytic rate is __________
A. Repressor
B. Inhibitor
C. Modulator
D. Regulator
Answer: B
Clarification: An inhibitor is a substance that interferes with the substrate-active site binding and slows down the catalytic rate.

8. Which of the following is an example for irreversible inhibitor?
A. Disulfiram
B. Oseltamivir
C. Protease inhibitors
D. DIPF
Answer: D
Clarification: Disulfiram, Oseltamivir and protease inhibitors are reversible inhibitors.

9. Which of the following is an example of reversible inhibitor?
A. DIPF
B. Penicillin
C. Iodoacetamide
D. Protease inhibitors
Answer: D
Clarification: DIPF, Penicillin and Iodoacetamide are irreversible inhibitors.

10. Where does inhibitor binds on enzyme in mixed inhibition?
A. At active site
B. Allosteric site
C. Does not bind on enzyme
D. Binds on substrate
Answer: B
Clarification: The inhibitor binds at a place different from active site allosterically.

11. The catalytic efficiency of two distinct enzymes can be compared based on which of the following factor?
A. K_m
B. Product formation
C. Size of the enzymes
D. pH of optimum value
Answer: A
Clarification: K_m is the substrate concentration. Increased substrate concentration increases the rate of reaction.

12. What is the general mechanism of an enzyme?
A. It acts by reducing the activation energy
B. It acts by increasing the activation energy
C. It acts by decreasing the pH
D. It acts by increasing the pH
Answer: A
Clarification: For the reaction to occur at a faster rate, activation energy should be less.

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Biochemistry Assessment Questions and Answers focuses on “Electron-Transfer reactions in Mitochondria”.

1. Protein that contains a nucleic acid derivative of riboflavin is called _________
A. Nucleic acid
B. Amino acid
C. Flavoprotein
D. None
Answer: C
Clarification: Flavoproteins contain a very tightly, sometimes covalently, bound flavin nucleotide, either FMN or FAD.

2. NADP-linked dehydrogenase catalyzes _________
A. Glucose 6-phosphate+NADP⁺ ↔ 6-phosphogluconate + NADPH + H⁺
B. Lactate + NAD⁺ ↔ pyruvate + NADH + H⁺
C. Pyruvate + CoA + NAD⁺ ↔ acetyl-CoA + CO₂ + NADH + H⁺
D. L-Malate + NAD⁺ ↔ oxaloacetate + NADH + H⁺
Answer: A
Clarification: NADP-linked dehydrogenase catalyzes Glucose 6-phosphate+NADP⁺ ↔ 6-phosphogluconate + NADPH + H⁺.

3. A lipid-soluble benzoquinone with a long isoprenoid side chain is?
A. Ubiquinone
B. Cytochrome b
C. Cytochrome c
D. Cytochrome a
Answer: A
Clarification: Ubiquinone also known as coenzyme Q is a lipid-soluble benzoquinone with a long isoprenoid side chain.

4. The only membrane bound enzyme in the citric acid cycle is _________
A. Succinate dehydrogenase
B. NADH dehydrogenase
C. ATP synthase
D. Acyl co-A dehydrogenase
Answer: A
Clarification: The only membrane bound enzyme in the citric acid cycle is succinate dehydrogenase.

5. The first step in the β oxidation of fatty acyl co-A is catalyzed by _________
A. Succinate dehydrogenase
B. NADH dehydrogenase
C. ATP synthase
D. Acyl co-A dehydrogenase
Answer: D
Clarification: It involves the transfer of electrons from the substrate to the FAD of the dehydrogenase, then to ETF.

6. Complex 1 is also called _________
A. NADH dehydrogenase
B. Succinate dehydrogenase
C. Cytochrome bc1 complex
D. Cytochrome oxidase
Answer: A
Clarification: Complex 2 is called succinate dehydrogenase.
Complex 3 is called the cytochrome bc1 complex.
Complex 4 is called cytochrome oxidase.

7. Complex 2 is also called _________
A. NADH dehydrogenase
B. Succinate dehydrogenase
C. Cytochrome bc1 complex
D. Cytochrome oxidase
Answer: B
Clarification: Complex 1 is called NADH dehydrogenase.
Complex 3 is called the cytochrome bc1 complex.
Complex 4 is called cytochrome oxidase.

8. Complex 3 is also called _________
A. NADH dehydrogenase
B. Succinate dehydrogenase
C. Cytochrome bc1 complex
D. Cytochrome oxidase
Answer: C
Clarification: Complex 1 is called NADH dehydrogenase.
Complex 4 is called cytochrome oxidase.
Complex 2 is called succinate dehydrogenase.

9. Complex 4 is also called _________
A. NADH dehydrogenase
B. Succinate dehydrogenase
C. Cytochrome bc1 complex
D. Cytochrome oxidase
Answer: D
Clarification: Complex 1 is called NADH dehydrogenase.
Complex 3 is called the cytochrome bc1 complex.
Complex 2 is called succinate dehydrogenase.

10. In mitochondria, hydride ions are removed from substrates by _________
A. NAD-linked dehydrogenases
B. NADP-linked dehydrogenases
C. ATP synthase
D. Succinate dehydrogenases
Answer: A
Clarification: In cytosol hydride ions are removed from substrates by NADP-linked dehydrogenases.

of Biochemistry Assessment Questions, .