Category: Biochemistry Objective Questions

Biochemistry Multiple Choice Questions on “Molecular Mechanisms of Signal Transduction”.

1. The information which is represented by a signal is detected by specific receptors and converted to a cellular response; this conversion is called _____________
A. Signal amplification
B. Signal transversion
C. Signal transduction
D. Signal integration
Answer: C
Clarification: The information which is represented by a signal is detected by specific receptors and converted to a cellular response; this conversion is called signal transduction.

2. Signal molecule fits the binding site on its complementary receptor called as _____________
A. Specificity
B. Amplification
C. Integration
D. Cooperativity
Answer: A
Clarification: Number of affected molecules increases geometrically in an enzyme cascade in amplification.
A regulatory outcome result from integrated input from both receptors is in integration.

3. Number of affected molecules increases geometrically in an enzyme cascade in _____________
A. Specificity
B. Amplification
C. Adaptation
D. Integration
Answer: B
Clarification: Signal molecule fits its binding site on its complementary receptor called as specificity.
Receptor is removed from cell surface in adaptation.
A regulatory outcome result from integrated input from both receptors is in integration.

4. Receptor is removed from cell surface in _____________
A. Specificity
B. Amplification
C. Adaptation
D. Integration
Answer: C
Clarification: A regulatory outcome result from integrated input from both receptors is in integration.
Signal molecule fits its binding site on its complementary receptor called as specificity.
Number of affected molecules increases geometrically in an enzyme cascade in amplification.

5. Regulatory outcome results from integrated input from both receptors is in _____________
A. Specificity
B. Amplification
C. Adaptation
D. Integration
Answer: D
Clarification: Receptor is removed from cell surface in adaptation.
Signal molecule fits binding site on its complementary receptor called as specificity.
Number of affected molecules increases geometrically in an enzyme cascade in amplification.

6. Acetylcholine receptor ion channel is an example of _____________
A. Gated ion channel
B. Receptor enzymes
C. Membrane protein
D. Nuclear protein
Answer: A
Clarification: Acetylcholine receptor ion channel is an example of gated ion channel.

7. How many types of signal transducers are there?
A. 3
B. 4
C. 5
D. 6
Answer: D
Clarification: Gated ion channels, receptor enzymes, membrane proteins that act through G protein, nuclear proteins, membrane proteins and adhesion receptors are the 6 types of signal transducers.

8. Which of the following is a nuclear receptor protein?
A. Steroid receptor
B. Adhesion receptor
C. Serpentine receptor
D. Receptor with no intrinsic enzyme activity
Answer: A
Clarification: Steroid receptor is a nuclear receptor protein.

9. Receptor proteins that indirectly activate enzymes that generate intracellular second messengers are _____________
A. Steroid receptors
B. Serpentine receptors
C. Adhesion receptors
D. Receptor enzymes
Answer: B
Clarification: Receptor proteins that indirectly activate enzymes that generate intracellular second messengers are serpentine receptors.

10. Insulin receptor is an example of _____________
A. Steroid receptors
B. Serpentine receptors
C. Adhesion receptors
D. Receptor enzymes
Answer: D
Clarification: Insulin receptor is nuclear receptor.

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Biochemistry Multiple Choice Questions on “Nucleotides & Nucleic Acids Basics”.

1. Identify the purine base of nucleic acids in the following.
A. Cytosine
B. Thymine
C. Uracil
D. Adenine
Answer: D
Clarification: Purines have two rings in their structure, but pyrimidine bases have only one ring. Adenine has two rings in its structure.

2. Which of the following are not the components of RNA?
A. Thymine
B. Adenine
C. Guanine
D. Cytosine
Answer: A
Clarification: Thymine is present in DNA but not in RNA.

3. Which of the following statements is true?
A. Sugar component of a nucleotide is ribose
B. Sugar component of a nucleotide is deoxyribose
C. The bases in nucleotides are attached to a pentose sugar moiety by a glycosidic linkage
D. The sugar molecule of the nucleotide is in L-configuration
Answer: C
Clarification: Sugar component of a nucleotide may be ribose or deoxyribose.

4. What is the composition of nucleoside?
A. a sugar + a phosphate
B. a base + a sugar
C. a base + a phosphate
D. a base + a sugar + phosphate
Answer: B
Clarification: A nucleoside is composed of a base and sugar.

5. What is the composition of nucleotide?
A. a sugar + a phosphate
B. a base + a sugar
C. a base + a phosphate
D. a base + a sugar + phosphate
Answer: D
Clarification: A nucleotide is composed of a base, a sugar and a phosphate.

6. Group of adjacent nucleotides are joined by ____________
A. Phosphodiester bond
B. Peptide bond
C. Ionic bond
D. Covalent bond
Answer: A
Clarification: The phosphodiester linkage joins 3’ carbon atom of one sugar molecule and 5’ carbon atom of another carbon atom.

7. The sugar molecule in a nucleotide is ____________
A. Pentose
B. Hexose
C. Tetrose
D. Triose
Answer: A
Clarification: Ribose or deoxyribose is a 5 carbon sugar.

8. Which of the following is true about phosphodiester linkage?
A. 5’-phosphate group of one nucleotide unit is joined to the 3’-hydroxyl group of the next nucleotide
B. 3’-phosphate group of one nucleotide unit is joined to the 5’-hydroxyl group of the next nucleotide
C. 5’-phosphate group of one nucleotide unit is joined to the 5’-hydroxyl group of the next nucleotide
D. 3’-phosphate group of one nucleotide unit is joined to the 3’-hydroxyl group of the next nucleotide
Answer: A
Clarification: 5’-phosphate group of one nucleotide unit is joined to the 3’-hydroxyl group of the next nucleotide.

9. Which of the following is false about purine and pyrimidine bases?
A. They are hydrophobic and relatively insoluble in water at the near-neutral pH of the cell
B. At acidic or alkaline pH the bases become charged and their solubility in water increases
C. Purines have two rings in their structure, but pyrimidine bases have only one ring
D. At acidic or alkaline pH the bases become charged and their solubility in water decreases
Answer: D
Clarification: At acidic or alkaline pH the bases become charged and their solubility in water increases.

10. Building blocks of nucleic acids are ____________
A. Nucleotides
B. Nucleosides
C. Amino acids
D. Histones
Answer: A
Clarification: Nucleotides are the building blocks of nucleic acids.

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Biochemistry Multiple Choice Questions on “Peptides and Proteins”.

1. During the formation of the peptide bond which of the following takes place?
A. Hydroxyl group is lost from its carboxyl group of one amino acid and a hydrogen atom is lost from its amino group of another amino acid
B. Hydrogen atom is lost from its carboxyl group of one amino acid and a hydroxyl group is lost from its amino group of another amino acid
C. Hydroxyl group is lost from its carboxyl group of one amino acid and a hydroxyl group is lost from its amino group of another amino acid
D. Hydrogen atom is lost from its carboxyl group of one amino acid and a hydrogen atom is lost from its amino group of another amino acid
Answer: A
Clarification: The α-amino group of one amino acid acts as a nucleophile to displace the hydroxyl group of another amino acid forming a peptide bond.

2. Peptide bond is a _________
A. Covalent bond
B. Ionic bond
C. Metallic bond
D. Hydrogen bond
Answer: A
Clarification: Two amino acids are covalently joined through a substituted amide linkage called a peptide bond.

3. A tripeptide has _________
A. 3 amino acids and 1 peptide bond
B. 3 amino acids and 2 peptide bonds
C. 3 amino acids and 3 peptide bonds
D. 3 amino acids and 4 peptide bonds
Answer: B
Clarification: Monopeptide is a peptide containing single amino acid, dipeptide contains two amino acids joined by one peptide bond and tripeptide contains three amino acids joined by two peptide bonds.

4. The factor which does not affect pK_a value of an amino acid is _________
A. The loss of charge in the α-carboxyl and α-amino groups
B. The interactions with other peptide R groups
C. Other environmental factors
D. Molecular weight
Answer: D
Clarification: The loss of charge in the α-carboxyl and α-amino groups, the interactions with other peptide R groups and other environmental factors can affect the pK_a.

5. Which of the following is a 39-residue hormone of the anterior pituitary gland?
A. Corticotropin
B. Glucagon
C. Insulin
D. Bradykinin
Answer: A
Clarification: Corticotropin is a 39-residue hormone of the anterior pituitary gland that stimulates the adrenal cortex.

6. The average molecular weight of an amino acid residue in a protein is about _________
A. 128
B. 118
C. 110
D. 120
Answer: C
Clarification: The average molecular weight of an amino acid residue is nearer to 128. Because a molecule of water is removed to create each peptide bond, average molecular weight is 128 – 18 = 110.

7. Which of the following is not the classified form of conjugated proteins?
A. Lipoproteins
B. Glycoproteins
C. Metalloproteins
D. Complete proteins
Answer: D
Clarification: On the basis of the chemical nature of their prosthetic groups conjugated proteins are classified into lipoproteins, glycoproteins and metalloproteins.

8. Which part of the amino acid gives it uniqueness?
A. Amino group
B. Carboxyl group
C. Side chain
D. None of the mentioned
Answer: C
Clarification: Different amino acids contain different side chains which make them unique.

9. Which of the following information is responsible to specify the three-dimensional shape of a protein?
A. The protein’s peptide bond
B. The protein’s amino acid sequence
C. The protein’s interaction with other polypeptides
D. The protein’s interaction with molecular chaperons
Answer: B
Clarification: The amino acid sequence of a protein determines its three-dimensional shape.

10. Unfolding of a protein can be termed as _________
A. Renaturation
B. Denaturation
C. Oxidation
D. Reduction
Answer: B
Clarification: The proteins lose their quaternary, tertiary, secondary structure and return to its native state by denaturation process.

11. What are the following is not a factor responsible for the denaturation of proteins?
A. pH change
B. Organic solvents
C. Heat
D. Charge
Answer: D
Clarification: pH change, organic solvents and heat are the factors responsible for the denaturation of proteins.

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Biochemistry Multiple Choice Questions on “General Features of Photophosphorylation”.

1. Which of the following statements about thylakoids is false?
A. They contain chlorophyll pigments
B. They contain the photosystems
C. They contain Calvin cycle enzymes
D. They contain the electron transport machinery
Answer: C
Clarification: Chloroplast stroma contains Calvin cycle enzymes and intermediates.

2. Which one of the following is the source of electrons in photosynthesis?
A. Carbohydrates
B. CO₂
C. Water
D. NADH
Answer: C
Clarification: Water is the source of electrons in photosynthesis. These electrons are required to reduce oxidized chlorophyll a molecules.

3. Which of the following about Calvin cycle is correct?
A. It is a metabolic pathway by which plants convert CO₂ into pentose sugars as the main product
B. With decrease in light intensity, the enzymes are more reactive
C. Rubisco adds CO₂ to 3-phosphoglycerate
D. It is a metabolic pathway by which plants convert CO₂ and water into carbohydrates
Answer: D
Clarification: CO₂ combines with ribulose 1, 5-bisphosphate.
The enzymes are more reactive if there is an increase in light intensity.

4. What are the favorable conditions for cyclic photophosphorylation?
A. Aerobic and optimum light
B. Aerobic condition only
C. Aerobic and low light intensity
D. Anaerobic and low light intensity
Answer: A
Clarification: Favorable conditions for cyclic photophosphorylation are aerobic and optimum light.

5. Hydrogen is transferred from the light reaction to the dark reaction in photosynthesis by _____________
A. DPN
B. NAD
C. ATP
D. NADP
Answer: A
Clarification: Diphosphopyridine nucleotide transfers hydrogen from the light reaction to the dark reaction in photosynthesis.

6. Calvin cycle occurs in ____________
A. Cytoplasm
B. Chloroplast
C. Mitochondria
D. Golgi body
Answer: A
Clarification: Calvin cycle occurs in cytoplasm.

7. Light energy is converted to chemical energy in the presence of ____________
A. Chloroplast
B. Ribosomes
C. Mitochondria
D. Stomata
Answer: A
Clarification: Photosynthetic pigment chlorophyll captures the energy from sunlight and converts it and stores it in energy-storage molecules ATP and NADPH.

8. Photosynthesis can be described as ____________
A. Reductive, anabolic, endergonic process
B. Reductive, anabolic, exergonic process
C. Oxidative, anabolic, endergonic process
D. Oxidative, catabolic, exergonic process
Answer: A
Clarification: Photosynthesis involves gaining of electrons; producing complex substances from simpler ones and requires energy.

9. Who is the first person to study the influence of light during photosynthesis?
A. Blackmann
B. Van Niel
C. J. Ingenhouz
D. Warburg
Answer: C
Clarification: Jan Ingenhouz was the best known to show that light is essential for photosynthesis.

10. The percentage of light energy fixed in photosynthesis is around ____________
A. 100%
B. 10%
C. 1%
D. 0.1%
Answer: C
Clarification: Around 1% of light energy is fixed in photosynthesis.

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Biochemistry Problems focuses on “Fates of Pyruvate under Anaerobic Conditions: Fermentation”.

1. Which of the following is true about the enzyme producing NADH from a triose phosphate in the glycolytic pathway?
A. It produces 1, 3-biphosphoglycerate and NADH
B. It catalyzes irreversible reaction
C. It uses NAD⁺ and dihydroxyacetone phosphate as substrates
D. It uses FADH₂ and glyceraldehyde 3-phosphate as substrates
Answer: A
Clarification: Triose phosphate, glyceraldehyde 3-phosphate is oxidized to 1, 3-biphosphoglycerate in the presence of dehydrogenase enzyme.

2. Which is the major factor(s) determining whether glucose is oxidized by aerobic or anaerobic glycolysis?
A. Ca⁺²
B. FADH₂
C. NADH and the ATP/ADP ratio
D. Presence of high AMP
Answer: C
Clarification: NADH and the ATP/ADP ratio are the major factors determining whether glucose is oxidized by aerobic or by anaerobic glycolysis.

3. When glucose is converted to lactate by anaerobic glycolysis, equivalent number of ATPs derived is?
A. 1
B. 2
C. 3
D. 4
Answer: B
Clarification: 2 ATP molecules are released when glucose is converted to lactate by anaerobic glycolysis.

4. When one molecule of glucose is oxidized to two molecules of lactate during anaerobic glycolysis, which of the following statements is false?
A. Glyceraldehyde 3-P dehydrogenase reaction produces 2 ATP molecules
B. Lactate dehydrogenase reaction produces no ATP
C. Pyruvate kinase reaction produces 2 ATP molecules
D. Phosphofructokinase-1 reaction uses 1 ATP molecule
Answer: A
Clarification: When one molecule of glucose is oxidized to two molecules of lactate during anaerobic glycolysis, Glyceraldehyde 3-P dehydrogenase reaction does not produce 2 ATP molecules.

5. In the reduction of pyruvate to lactate, which of the following is regenerated?
A. H⁺
B. NADH
C. NAD⁺
D. Na⁺
Answer: C
Clarification: NAD⁺ is regenerated from NADH by the reduction of pyruvate to lactate.

6. For its activity, pyruvate decarboxylase requires ______________
A. Mg⁺²
B. Ca⁺²
C. Na⁺
D. H⁺
Answer: A
Clarification: Pyruvate decarboxylase requires Mg⁺² in the conversion of pyruvate to acetaldehyde.

7. TPP (thiamine pyrophosphate) is derived from ____________
A. Vitamin A
B. Vitamin B1
C. Vitamin C
D. Vitamin B2
Answer: B
Clarification: TPP is a coenzyme derived from vitamin B1 (thiamine).

8. What are the end products in ethanol fermentation?
A. Ethanol and CO₂
B. Ethanol and O₂
C. Ethanol, H₂ and CO₂
D. Ethanol, O₂ and CO₂
Answer: A
Clarification: Overall equation of ethanol fermentation:
Glucose +2ADP + 2P_i → 2 ethanol + 2CO₂ + 2ATP + 2H₂O.

9. Which enzyme is involved in the pathway of ethanol fermentation?
A. Hexokinase
B. Pyruvate decarboxylase
C. Pyruvate dehydrogenase
D. Pyruvate kinase
Answer: B
Clarification: Decarboxylation of pyruvate is catalyzed by pyruvate decarboxylase.

10. Which enzyme is involved in the pathway of synthesis of acetyl-coA?
A. Hexokinase
B. Pyruvate decarboxylase
C. Pyruvate dehydrogenase
D. Pyruvate kinase
Answer: C
Clarification: In the synthesis of acetyl-coA, pyruvate dehydrogenase is involved.

of Biochemistry Problems, .

Biochemistry Multiple Choice Questions on “Solute Transport across Membranes”.

1. Erythrocyte glucose transporter is an example of ____________
A. Ion driven active transport
B. Facilitated diffusion
C. Active transport
D. Simple diffusion
Answer: B
Clarification: Transportation is facilitated by carrier proteins.

2. Which out of the following is not mediated transport?
A. Facilitated diffusion
B. Primary active transport
C. Secondary active transport
D. Simple diffusion
Answer: D
Clarification: Simple diffusion is not mediated transport.

3. Na⁺ glucose transporter is an example of ____________
A. Symport
B. Antiport
C. Facilitated diffusion
D. ATP driven active transport
Answer: A
Clarification: Substrates are moved in the same direction across the membrane.

4. Which of the following is energy independent?
A. Active transport
B. Primary active transport
C. Secondary active transport
D. Passive transport
Answer: D
Clarification: Active transport is ATP dependent.

5. Semipermeable membrane allows ____________
A. Solute to pass
B. Solution to pass
C. Solvent to pass
D. Proteins to pass
Answer: C
Clarification: Semipermeable membrane allows solvent to pass.

6. When does saturation occur?
A. When molecules are moved by the use of vesicles
B. When the energy from a high-energy bond is required to move molecules
C. When a group of carrier proteins is operating at its maximum rate
D. When a carrier molecule has the ability to transport only one molecule or a group of closely related molecules
Answer: C
Clarification: When a group of carrier proteins is operating at its maximum rate saturation occurs.

7. In which of the following means of transport a cell expels large molecules out of it?
A. Phagocytosis
B. Exocytosis
C. Endocytosis
D. Diffusion
Answer: B
Clarification: In exocytosis, a cell expels large molecules out of it.

8. HCO₃^– – Cl^– transporter is an example of ____________
A. Uniport
B. Antiport
C. Symport
D. Facilitated diffusion
Answer: B
Clarification: Substrates are moved in the opposite direction.

9. Which of the following transports only one kind of substrate?
A. Uniport carriers
B. Symport carriers
C. Antiport carriers
D. Membrane proteins
Answer: A
Clarification: Symport carriers move two or more substrates in the same direction across the membrane.
Antiport carriers move substrates in the opposite direction.

10. Which of the following induces conformational change in protein?
A. Uniport
B. Symport
C. Antiport
D. Facilitated diffusion
Answer: D
Clarification: Facilitated diffusion induces a conformational change in protein.

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