Category: Biochemistry Objective Questions

Biochemistry Multiple Choice Questions on “Regulation of Metabolic Pathways”.

1. Which out of the following statements is true about the regulation of metabolic pathway?
A. Most of the metabolic pathways are regulated
B. Most of the metabolic pathways are not regulated
C. Regulation of metabolic pathways always involves changing the amount of enzymes
D. Metabolic regulation always depends on control by hormones
Answer: A
Clarification: According to the physiological needs, rate of metabolism needs to be changed.

2. The rate of breakdown of metabolites is termed as ___________
A. Metabolic state
B. Metabolism
C. Steady state
D. Homeostasis
Answer: C
Clarification: The rate of breakdown of metabolites is termed as a steady state.

3. Diminished delivery of oxygen to tissues is termed as ___________
A. Hypoxia
B. Ischemia
C. Homeostasis
D. Metabolism
Answer: A
Clarification: Diminished delivery of oxygen to tissues is termed as hypoxia.

4. Diminished flow of blood to tissues is termed as ___________
A. Hypoxia
B. Ischemia
C. Homeostasis
D. Metabolism
Answer: B
Clarification: Diminished flow of blood to tissues is termed as ischemia.

5. Which of the following statements is true about the control of muscle glycogen phosphorylase?
A. It is activated by phosphorylation by an active phosphorylase kinase
B. It is allosterically activated by ATP
C. It is allosterically activated by cAMP
D. Normally it exists in active form
Answer: A
Clarification: It is allosterically inhibited by ATP. It is partially activated allosterically by AMP. Normally it exists in inactive form.

6. Which of the following is not a factor determining the activity of an enzyme?
A. Association with regulatory protein
B. Sequestration
C. Allosteric regulation
D. Nucleotides
Answer: D
Clarification: Association with regulatory protein, sequestration, allosteric regulation and covalent modification are the factors determining the activity of an enzyme.

7. Which of the following statements is true?
A. High insulin/glucagon ratio activates lipolysis in muscle
B. High insulin/glucagon ratio inhibits lipolysis in liver
C. High insulin/glucagon ratio activates lipolysis in adipocytes
D. Low insulin/glucagon ratio activates lipolysis in adipocytes
Answer: D
Clarification: A high insulin/glucagon inactivates lipolysis.

8. Which of the following type of metabolites is used for generating glucose under severe starvation conditions?
A. Amino acids
B. Fats
C. Glycogen
D. Starch
Answer: A
Clarification: Fats cannot be converted to glucose; there is no store of carbohydrate. Only amino acids can be used for generating glucose under severe starvation conditions.

9. Which of the following statements is true about brain metabolism in starvation?
A. The brain can use glucogenic amino acids for energy
B. The brain can only use glucose as fuel
C. Up to a quarter of energy requirement of the brain can come from fatty acids
D. Up to a half of energy requirement of the brain can come from ketone bodies
Answer: A
Clarification: Brain does not use amino acids directly but glucose derived from glucogenic amino acids in the liver.

10. Which one of the following statements about the control of enzyme activity by phosphorylation is correct?
A. Phosphorylation of an enzyme results in a conformational change
B. Phosphorylation of an enzyme occurs only at specific tyrosine residues
C. Phosphorylation of an enzyme is carried out by phosphoprotein phosphatases
D. Enzyme control by phosphorylation is irreversible
Answer: A
Clarification: Phosphorylation of enzyme is reversible; phosphorylation is not carried out by phosphoprotein phosphatases.

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Biochemistry Multiple Choice Questions on “Receptor Enzymes”.

1. SH₂ domain specifically binds to _____________
A. GDP
B. Ca⁺²
C. Phosphorylated tyrosine residues
D. Phosphorylated serine residues
Answer: C
Clarification: Phosphorylated tyrosine residues specifically binds SH₂ domain during signal transduction.

2. cAMP and cGMP are derived from ____________
A. ATP and GTP by the actions of guanylate cyclase and adenylate cyclase respectively
B. ATP and GTP by the actions of adenylate cyclase and gualnlate cyclase respectively
C. GTP and ATP by the actions of adenylate cyclase and guanylate cyclase respectively
D. None of the mentioned
Answer: B
Clarification: cGMP is derived from GTP by the actions of guanylate cyclase and
cAMP is derived from ATP by the actions of adenylate cyclase respectively.

3. Which of the following is false about phosphorylation by IRS on serine residue?
A. It is an inhibitory phosphorylation
B. It is molecular mechanism for insulin resistance
C. It increases insulin levels
D. Target tissues fail to respond to circulating insulin
Answer: C
Clarification: Inhibitory serine phosphorylation is a molecular mechanism for insulin resistance which is a condition where target tissues fail to respond to circulating insulin.

4. The enzyme activated by cyclic AMP, passing on the hormonal signal is ____________
A. Protein kinase B
B. Protein kinase A
C. Protein kinase C
D. G protein receptor kinase
Answer: B
Clarification: Protein kinase A is activated by cyclic AMP, passing on the hormonal signal.

5. Protein kinase ERK is activated by phosphorylation of ____________
A. Only Thr
B. Only Tyr
C. Both Thr and Tyr
D. Only Ser
Answer: C
Clarification: Both Thr and Tyr are phosphorylated to activate the protein kinase ERK.

6. Activation of guanylyl cyclase produces ____________
A. Guanosine 3’, 5’-cyclic monophosphate
B. Guanosine 2’, 5’-cyclic monophosphate
C. Guanosine 4’, 5’-cyclic monophosphate
D. Guanosine 1’, 5’-cyclic monophosphate
Answer: A
Clarification: Guanosine 3’, 5’-cyclic monophosphate is produced by the activation of guanylyl cyclase.

7. cGMP-dependent protein kinase is also called ____________
A. Protein kinase B
B. Protein kinase A
C. Protein kinase G
D. Protein kinase C
Answer: C
Clarification: cGMP-dependent protein kinase is also called protein kinase G.

8. Which of the following is not responsible of producing diarrhea?
A. Elevation in [cGMP]
B. Increase in Cl^– secretion
C. Decrease in reabsorption of water by the intestinal epithelium
D. Decrease in Cl^– secretion
Answer: D
Clarification: Elevation in [cGMP] leads to increase in Cl^– secretion and decrease in reabsorption of water by the intestinal epithelium.

9. Which of the following is a short-lived messenger that acts by stimulating a soluble guanylyl cyclase, raising [cGMP] and stimulating PKG?
A. NO
B. NO₂
C. NO₃^–
D. N₂O
Answer: A
Clarification: NO is a short-lived messenger that acts by stimulating a soluble guanylyl cyclase, raising [cGMP] and stimulating PKG.

10. Ras protein is a ____________
A. G-protein switch
B. Small monomeric GTPase switch protein
C. Serine-threonine kinase
D. Tyrosine kinase
Answer: B
Clarification: Ras protein is a small monomeric GTPase switch protein, involved in transmitting signals within cells.

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Biochemistry Multiple Choice Questions on “Nucleic Acid Chemistry”.

1. What happens in hypochromicity?
A. When DNA is in bound form, there is decrease in absorption of UV light
B. When DNA is in bound form, there is increase in absorption of UV light
C. When DNA is in unbound form, it is more stable
D. When DNA is in unbound form, there is decrease in absorption of UV light
Answer: A
Clarification: It describes the decrease in absorbance of UV light in a double stranded DNA.

2. What happens in hyperchromicity?
A. When DNA is in bound form, there is decrease in absorption of UV light
B. When DNA is in bound form, there is increase in absorption of UV light
C. When DNA is in unbound form, it is more stable
D. When DNA is in unbound form, there is increase in absorption of UV light
Answer: D
Clarification: It describes the increase in absorption of UV light in a single stranded DNA.

3. Which of the following is true about t_m?
A. It can be termed as renaturation temperature
B. The higher the content of G ≡ C base pairs, the higher the t_m
C. The higher the content of A = T base pairs, the higher the t_m
D. The higher the content of G ≡ C base pairs, the lower the t_m
Answer: B
Clarification: T_m is the melting temperature or denaturation temperature.

4. Which of the following is false?
A. The stability of an RNA-DNA hybrid is generally intermediate between that of RNA and DNA
B. RNA duplexes are more stable than DNA duplexes
C. DNA duplexes are more stable than RNA duplexes
D. DNA duplexes are less stable than RNA- DNA hybrid
Answer: C
Clarification: RNA duplexes are more stable than DNA duplexes.

5. DNA denaturation is measured by absorbance at ___________
A. 220nm
B. 230nm
C. 250nm
D. 260nm
Answer: D
Clarification: At 260nm absorbance, DNA denaturation is measured.

6. Which of the following is false about denaturation?
A. Disruption of hydrogen bonds
B. Disruption of phosphodiester linkage
C. Loss of helical structure of DNA
D. It is resulted as a result of change in pH or increase in temperature
Answer: B
Clarification: Phosphodiester linkages are not broken by denaturation.

7. Which of the following nucleotides is not present in RNA?
A. AMP
B. GMP
C. CMP
D. TMP
Answer: D
Clarification: Thymidine monophosphate is present in DNA.

8. Which of the following nucleotides is not present in DNA?
A. AMP
B. GMP
C. CMP
D. UMP
Answer: D
Clarification: Uridine monophosphate is present in RNA.

9. Which of the following is false?
A. RNA does not obey Chargaff’s rule
B. DNAs can be identified by Orcinol color reaction
C. In RNA OH group is present at 2’ position
D. Alkali hydrolyses RNA to 2’3’-cyclic diesters
Answer: B
Clarification: RNAs can be identified by Orcinol color reaction.

10. Which of the following involves carrying genetic information from DNA for protein synthesis?
A. m-RNA
B. t-RNA
C. r-RNA
D. sn-RNA
Answer: A
Clarification: Messenger RNA carries genetic information from DNA for protein synthesis.

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Biochemistry Multiple Choice Questions on “The Covalent Structure of Proteins”.

1. Which of the following statements is false?
A. Primary structure of a protein determines how it folds up into a unique three dimensional structure
B. Secondary structure of a protein determines how it folds up into a unique three dimensional structure
C. Three dimensional structure of a protein determines the function of a protein
D. Amino acid sequence is absolutely invariant for a particular protein
Answer: B
Clarification: Primary structure of a protein determines how it folds up into a unique three dimensional structure, which in turn determines the function of a protein.

2. Who deduced the double-helical structure of DNA?
A. Frederick Sanger
B. Mendel
C. Watson and Francis Crick
D. Anton van Leeuwenhoek
Answer: C
Clarification: In 1953 James D. Watson and Francis Crick deduced the double-helical structure of DNA and proposed a structural basis for its precise replication.

3. Two chains of amino acids in an insulin molecule are held together by __________
A. Sulfide bridges
B. Disulfide bridges
C. Peptide bond
D. Covalent linkage
Answer: B
Clarification: When we consider amino acid sequence of bovine insulin, the two peptide chains are joined together by disulfide cross linkages.

4. Tertiary conformation of proteins is maintained by 3 types of bonds namely ionic, hydrogen and __________
A. Sulfide
B. Disulfide
C. Covalent
D. Peptide
Answer: B
Clarification: Ionic interactions, hydrogen and disulfide linkages stabilizes tertiary structure of a protein.

5. Hemoglobin is a __________
A. Monomer
B. Dimer
C. Trimer
D. Tetramer
Answer: D
Clarification: It is a tetramer with 2 α chains and 2β chains.

6. Which of the following is false?
A. The two main types of secondary structure are the α helix and β pleet structures
B. α helix is a right handed coiled strand
C. The hydrogen bonding in a β-sheet is between strands rather than within strands
D. The hydrogen bonding in a β-sheet is within strands rather than between strands
Answer: D
Clarification: The sheet conformation consists of a pair of strands lying side-by-side. The carbonyl oxygen in one strand hydrogen bond with the amino hydrogen of the adjacent strand.

7. Native state of a protein can be disrupted by __________
A. Temperature
B. pH
C. Removal of water
D. Presence of hydrophilic surfaces
Answer: D
Clarification: Native state of a protein can be disrupted by temperature, pH, Removal of water and presence of hydrophobic surfaces.

8. Which of the following is true?
A. The disulfide bridges formed by reduction of the sulfhydryl groups on cysteine stabilizes protein tertiary structure
B. The disulfide bridges formed by oxidation of the sulfhydryl groups on cysteine destabilizes protein tertiary structure
C. The disulfide bridges formed by oxidation of the sulfhydryl groups on cysteine stabilizes protein tertiary structure
D. The disulfide bridges formed by reduction of the sulfhydryl groups on cysteine destabilizes protein tertiary structure
Answer: C
Clarification: The disulfide bridge formed by oxidation of the sulfhydryl groups on cysteine stabilizes protein tertiary structure, allowing different parts of the protein chain to be held together covalently.

9. Identify the wrong statement.
A. Hemoglobin is a globular protein
B. Hemoglobin is a fibrous protein
C. Fibrous proteins are insoluble in water
D. Collagen is a fibrous protein
Answer: B
Clarification: Hemoglobin is a globular protein and collagen is a fibrous protein.

10. In 3° structure of proteins, folding and shaping is done by __________
A. Hydrophobic interactions
B. Polar interactions
C. Hydrogen bonding
D. None of the mentioned
Answer: A
Clarification: Globular proteins have a tertiary structure with hydrophobic amino acid residues and a surface region of hydrophilic residues; these hydrophobic interactions are responsible for the folding and shaping of 3° structure of proteins.

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Biochemistry Multiple Choice Questions on “ATP Synthesis by Photophosphorylation”.

1. If 8 photons are required to produce one molecule of O₂, how many photons are required to produce one molecule of glucose?
A. 6
B. 8
C. 48
D. 12
Answer: C
Clarification: 6 molecules of O₂ must be produced during the production of glucose, so 6×8=48 photons are required for producing one molecule of glucose.

2. When compared to retinal, chlorophyll can be described as a pigment that has a ____________
A. Narrow absorption range but high efficiency
B. Narrow absorption range but low efficiency
C. Wide absorption range but high efficiency
D. Wide absorption range but low efficiency
Answer: A
Clarification: Chlorophyll has a narrow absorption range but high efficiency compared to retinal.

3. Which of the following is the correct sequence for the movement of electrons during the light-dependent reactions of plants?
A. P₇₀₀, P₆₈₀, NADP⁺, water
B. P₆₈₀, water, P₇₀₀, NADP⁺
C. Water, P₇₀₀, NADP⁺, P₆₈₀
D. Water, P₆₈₀, P₇₀₀, NADP⁺
Answer: D
Clarification: The sequence for the movement of electrons firstly includes water, secondly P₆₈₀ then P₇₀₀ and finally NADP⁺.

4. Which pigment is used in human vision?
A. Retinal
B. Vitamin A
C. Ferredoxin
D. Beta-carotene
Answer: A
Clarification: Retinal is used in human vision.

5. Why light is required for light dependent reactions?
A. It splits ATP molecules which generates the energy necessary to power the light independent reactions
B. It is the source for electrons
C. It splits the water molecules
D. It energizes electrons in the reaction center
Answer: D
Clarification: Light energizes electrons in the reaction center, so it is required for light dependent reactions.

6. Photosynthesis takes place in sac like membranes called ___________
A. Thylakoids
B. Grana
C. Photosystems
D. Photons
Answer: A
Clarification: Photosynthesis takes place in thylakoid structures.

7. The carbon-assimilation reactions require ATP and NADPH in the ratio ___________
A. 3:2
B. 2:3
C. 3:4
D. 4:3
Answer: A
Clarification: The carbon-assimilation reactions require ATP and NADPH in the ratio 3:2.

8. Which of the following systems has an associated water splitting activity resembling that of plants?
A. Photosystem
B. Photosystem I
C. Photosystem II
D. Photosystem III
Answer: C
Clarification: Photosystem II has an associated water splitting activity resembling that of plants.

9. The earliest photo synthesizers used which of the following as the source of hydrogen?
A. CO₂
B. C₆H₁₂O₆
C. H₂O
D. H₂S
Answer: D
Clarification: The earliest photo synthesizers used H₂S as the source of hydrogen.

10. Photosystem I used which of the following in its photo-center?
A. P700
B. P800
C. P900
D. P600
Answer: A
Clarification: Photosystem I used P700 in its photo-center.

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Biochemistry Multiple Choice Questions on “Pentose Phosphate Pathway of Glucose Oxidation”.

1. In the pentose phosphate pathway, the major products are ____________
A. Ribulose and NADPH
B. Ribulose and NADH
C. Ribulose and NAD⁺
D. Ribulose and ATP
Answer: A
Clarification: The products formed are pentose, ribulose and NADPH.

2. What is the first reaction of the pentose phosphate pathway?
A. Oxidation of glucose 6-phosphate to 6-phosphoglucono-δ-lactone
B. Oxidation of 6-phosphogluconate to ketopentose ribulose 5-phosphate
C. Reduction of 6-phosphoglucono-δ-lactone to glucose 6-phosphate
D. Reduction of ketopentose ribulose 5-phosphate to 6-phosphogluconate
Answer: A
Clarification: The first reaction of the pentose phosphate pathway is the oxidation of glucose 6-phosphate to 6-phosphoglucono-δ-lactone by glucose 6-phosphate dehydrogenase.

3. Which of the following statements is correct about oxidative pentose phosphate pathway?
A. It generates NADH
B. It oxidizes NADPH to NADP⁺
C. The pathway supplies ribose 5-phosphate and NADPH in the quantities the cell requires
D. Glucose 6-phosphatase catalyzes the rate limiting reaction of the pathway
Answer: C
Clarification: Oxidative pentose phosphate pathway supplies ribose 5-phosphate and NADPH in the quantities the cell requires. It reduces NADP⁺ to NADPH.

4. Which one out of the following enzymes acts in the pentose phosphate pathway?
A. Aldolase
B. Glycogen phosphorylase
C. Pyruvate kinase
D. 6-phosphogluconate dehydrogenase
Answer: D
Clarification: The first reaction in pentose phosphate pathway is catalyzed by 6-phosphogluconate dehydrogenase.

5. Oxidation of 3 molecules of glucose by pentose phosphate pathway results in the production of ____________
A. 3 molecules of pentose, 6 molecules of NADPH and 3 molecules of CO₂
B. 4 molecules of pentose, 6 molecules of NADPH and 3 molecules of CO₂
C. 4 molecules of pentose, 3 molecules of NADPH and 3 molecules of CO₂
D. 3 molecules of pentose, 4 molecules of NADPH and 3 molecules of CO₂
Answer: A
Clarification: Glucose 6-phosphate + 2NADP⁺ + H₂O → ribose 5-phosphate + CO₂ + 2NADPH + 2H⁺.

6. What is the main function of the pentose phosphate pathway?
A. Supply NADP⁺
B. Supply NADH
C. Supply energy
D. Supply pentoses and NADPH
Answer: D
Clarification: The main function of pentose phosphate pathway is to supply pentoses to NADPH.

7. Which one of the following statements is correct about the pentose phosphate pathway?
A. It generates 6 moles of CO₂ for each mole of glucose consumed
B. It generates 38 mol of ATP per mole of glucose consumed
C. It is a reductive pathway that consumes NADH
D. Present in plants but not in animals
Answer: A
Clarification: There is the continued production of NADPH and converting glucose 6-phosphate (in six cycles) to CO₂.

8. Which of the following statements is correct about the reductive pentose phosphate pathway?
A. It is not reversible
B. Transketolase transfers 3 carbon units
C. Transaldose transfers 2 carbon units
D. Pentoses can provide glycolytic intermediates
Answer: D
Clarification: It is reversible, transketolase transfers 2 carbon units and transaldose transfers 3 carbon units.

9. The use of NADPH generated from pentose phosphate pathway cannot be ____________
A. oxidized in the electron transport chain to provide 38 ATPs
B. Used for the synthesis of fatty acids
C. Used for the macrophageal functions
D. Used for steroid synthesis
Answer: A
Clarification: NADPH cannot be oxidized in the electron transport chain to provide 38 ATPs.

10. Conversion of xylulose 5-phosphate to ribulose 5-phosphate is catalyzed by ___________
A. Phosphopentose epimerase
B. Transaldolase
C. Transketolase
D. Phosphopentose isomerase
Answer: A
Clarification: Conversion of xylulose 5-phosphate to ribulose 5-phosphate is catalyzed by epimerase.

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