Category: Cell Biology Objective Questions

Tricky Cell Biology Questions and Answerson “Enzymes as Biological Catalysts”.

1. Why are enzymes required?
A. Enzymes help to yield more product
B. Enzymes increase the activation energy of the reaction
C. Enzymes decrease the activation energy of the reaction
D. Enzymes maintain the equilibrium in the reaction
Answer: C
Clarification: Chemical reactions need certain covalent bond breakage within the reactants. For this, the reactants must contain sufficient kinetic energy called the activation energy. Enzymes act as catalysts that speed up the reaction by lowering the activation energy required for breaking the covalent bonds.

2. Competitive enzyme inhibitors are ________
A. Reversible inhibitors
B. Irreversible inhibitors
C. Permanent inhibitors
D. None of the mentioned
Answer: A
Clarification: Irreversible inhibitors are those that bind very tightly to an enzyme, often by forming a covalent bond to one of its amino acid residues. Reversible inhibitors bind loosely to an enzyme and thus are readily displaced. Competitive inhibitors are reversible inhibitors of enzyme that compete with a substrate for access to the active site of the enzyme.

3. Which of the following is a non-competitive inhibitor against protease produced by HIV?
A. Tipranavir
B. Acetylcholinesterase
C. Ritonavir
D. Phenicols
Answer: A
Clarification: In noncompetitive inhibition, the substrate and inhibitor do not compete for the active site of the enzyme and the inhibitor generally act at other site to bind to the enzyme. The level of inhibition depends on concentration of the inhibitor. Tipranavir is non-competitive inhibitor of the protease produced by HIV when HIV infects a white blood cell. Ritonavir is a competitive inhibitor of the protease and resembles the its peptide substate.

4. Allosteric enzymes are which _______
A. Have single subunit
B. Have multiple subunits
C. Follows Michaelis-Menten kinetics
D. Do not affect the binding affinity
Answer: B
Clarification: Allosteric enzymes are enzymes that change conformation upon binding of an effector and affects the binding affinity at a different binding site. Allosteric enzymes are the exception to Michaelis-Menten kinetics and usually has multiple coupled subunits or domains.

5. Feedback inhibition occurs due to _______
A. Excess of the reactants in the reaction
B. Presence of competitive inhibitor
C. Increase in product to a certain level
D. Presence of irreversible inhibitor
Answer: C
Clarification: Feedback inhibition refers to the inhibition of enzyme activity when a certain end product is increased beyond a certain level. Due to accumulation of the product, the enzyme does form the enzyme-substrate complex in order to form the product, which is already in excess.

6. Enzymes that transfer the phosphate group from one protein to another is called _____
A. Phosphatase
B. Phosphate transferase
C. Kinase
D. Phosphorylase
Answer: C
Clarification: Kinase is the enzyme that transfers phosphate group from one protein to another. Phosphorylase catalyzes addition of phosphate group from an inorganic phosphate to an acceptor. Phosphatase enzyme cleaves a phosphate in presence of water.

7. The enzyme that catalyzes the transfer of a proton from a reactant to NAD+ is known as ______
A. Hydrolase
B. Proton carrier
C. Dehydrogenase
D. None of the mentioned
Answer: C
Clarification: Dehydrogenase is the enzyme that catalyzes the removal of a proton tor hydrogen from a reactant to NAD+. NADH is the reduced form of NAD+, which is a cofactor in the electron transport chain.

8. The functions of ATP are ___________
A. ATP acts as the main source of energy in cells
B. Plays a role in transporting solutes and proteins across cell membranes
C. Contribute to the building blocks of DNA
D. All of the mentioned
Answer: D
Clarification: Adenosine triphosphate or ATP is the main source of energy in cells. It releases energy by breaking into Adenosine diphosphate (ADP) and inorganic phosphate. It plays a role in solute transport across cell membranes through ATPase channels. It is the precursor of Adenine, which helps in the formation of DNA.

9. In anaerobic respiration, pyruvic acid is converted to _______
A. Lactate
B. Acetyl CoA
C. PEP
D. Acetate
Answer: A
Clarification: In aerobic respiration, the pyruvate is converted to two-carbon compound acetyl CoA which enters the Kreb’s cycle to release carbon dioxide and energy. In anaerobic respiration, due to absence of oxygen, the pyruvate is converted to lactate. In yeast fermentation, pyruvate is converted to alcohol and carbon dioxide.

10. The cofactor in Haber’s process is __________
A. Molybdenum
B. Iron
C. Copper
D. Magnesium
Answer: A
Clarification: The process of formation of ammonia from hydrogen and nitrogen is known as the Haber’s process. The enzyme that catalyzes the Haber’s reaction needs Molybdenum (Mo) as a cofactor.

To practice Tricky questions and answers on all areas of Cell Biology,

Cell Biology Multiple Choice Questions on “Aerobic Respiration – Proton Motive Force”.

1. The free energy released during electron transport is utilized to move protons from _____________ to inner membrane and cytosol.
A. extracellular environment
B. outer membrane
C. nucleus
D. matrix
Answer: D
Clarification: The free energy released in the electron transport moves protons from matrix to inner membrane and cytosol of the mitochondrion.

2. Proton motive force is the net sum of how many gradient components?
A. 1
B. 2
C. 3
D. 4
Answer: B
Clarification: Proton motive force is a measure of electrochemical gradient. Because the translocation of protons across the membrane lead to a difference of hydrogen ion concentration and a difference of charge, the energy present in both components of the proton electrochemical gradient are combined and expressed as proton motive force.

3. The contribution made by electric potential versus pH gradient to the proton motive force (Δp) is determined by which property of the mitochondrial membrane?
A. thickness
B. position in the cell
C. permeability
D. number of cristae
Answer: C
Clarification: The contribution made by electric potential versus pH gradient is determined by the permeability of the membrane. For example if at a particular instance, membrane is permeable to Cl- ions the electric potential gradient is reduced without affecting the proton gradient.

4. The approximate proton motive force of an actively respiring mitochondrion is ____________ mV.
A. 220
B. 240
C. 260
D. 280
Answer: A
Clarification: The approximate proton motive force that an actively respiring mitochondrion generates across its inner membrane is 220 mV. In mammalian mitochondria, 80 percent is represented by the voltage component and 20 percent by proton concentration.

5. The maintenance of proton motive force requires that inner mitochondrial membrane remains permeable to protons.
A. True
B. False
Answer: B
Clarification: The inner mitochondrial membrane must remain highly impermeable to protons otherwise the gradient established by electron transport would be quickly dissipated by the leakage of protons back into the matrix.

6. For which organelle proton motive force is also a source of energy?
A. nucleus
B. ribosomes
C. mitochondrion
D. golgi complex
Answer: C
Clarification: Other than hydrolysis of ATP, mitochondrion has alternate sources of energy one of which is proton motive force. It drives the uptake of ADP in exchange of ATP; and can also be used to pull calcium ions into the mitochondrion.

Cell Biology Multiple Choice Questions on “Extracellular Matrix and Cell Interactions – Gap Junctions and Plasmodesmata”.

1. Who discovered plasmodesmata?
A. Strasburger
B. Boveri
C. J Rhodin
D. Van Beneden
Answer: A
Clarification: Plasmodesmata serves as a connective system between two plant cells and in some algal cells. These were first discovered by Strasburger in 1901. The discovery was aided by electron microscopic studies.

2. Gap junctions are otherwise known as plasmodesmata.
A. True
B. False
Answer: B
Clarification: Plasmodesmata and gap junctions are similar in function but they have difference in their structures. Gap junctions helps substance pass through the cell membranes while the plasmodesmata forms a connection between the two cells.

3. How many plasmodesmata are present in a plant cell?
A. 10
B. 100
C. 1000
D. 5
Answer: C
Clarification: The plant cells have around 1000 plasmodesmata, which connects them with the neighboring cells. These plasmodesmata serves as a channel, which helps the transfer of materials from one cell to another.

4. Gap junctions are absent in __________
A. Sperm cells
B. Reproductive cells
C. Cardiac cells
D. Brain cells
Answer: A
Clarification: Gap junctions are absent in all the cell that are motile. Gap junctions are also absent in erythrocytes. These motile cells do not have a necessity for the passage of molecules or ions.

5. What is the gap junction in nerves called?
A. Chemical synapse
B. Electrical synapse
C. Post synapse
D. Pre synapse
Answer: B
Clarification: The nerves and the neurons have the gap junctions, which helps them in the transmission of electrical signals from one nerve cell to another called electrical synapse. These coexist with chemical synapse.

6. What is the diameter of a gap junction?
A. 2.2 – 3 nm
B. 3 – 3.2 nm
C. 1.2 – 2 nm
D. 0.2 – 2 nm
Answer: C
Clarification: The gap junctions have a wide diameter of about 1.2 – 2 nm. These gap junctions are capable of allowing molecules that are slightly larger than the normal sized ones.

7. What is the chemical formula for rotigaptide?
A. C₂₈H₃₉N₇O₉
B. C₂₈H₃₉N₇O₈
C. C₂₈H₃₈N₇O₉
D. C₂₇H₃₉N₇O₉
Answer: A
Clarification: Rotigaptide has a chemical formula of C₂₈H₃₉N₇O₉ which is shortly known as ZP-123. This is a drug which is now used to treat atrial fibrillation. This drug has shown to increase the conductance of gap junctions in cardiac muscle cells.

8. Which cell organelle covers the plasmodesmata of the cells?
A. Ribosome
B. Nucleus
C. Rough endoplasmic Reticulum
D. Smooth endoplasmic reticulum
Answer: D
Clarification: The plasmodesmata in exclusively present in plant cells. These are covered by the smooth endoplasmic reticulum of both the cells. This helps in the transport of materials across the cells.

9. Which genetic disorder is associated with dysfunction of gap junction?
A. Vohwinkel’s syndrome
B. Down’s syndrome
C. Zellweger Syndrome
D. Bubble Boy Syndrome
Answer: A
Clarification: Vohwinkel’s syndrome is a skin disease caused by a disorder in the gap junction. It is characterized by thick calluses in the palms of hands and foot. This disease is seen in the infant stages or early childhood.

10. Which of the following disease associated with the nervous system is caused by disorder in gap junctions?
A. Parkinson’s disease
B. Brain ischemia
C. Stroke
D. Seizures
Answer: B
Clarification: Brain ischemia, otherwise known cerebral ischemia where the blood flow to the brain is constricted. The gap junctions are unable to provide oxygen thus the brain undergoes hypoxia. This situation is permanent if it is untreated for prolonged time.

Cell Biology Multiple Choice Questions on “Cells Basic Properties”.

1. Parts of a cell can be isolated and cultured in a laboratory.
A. True
B. False
Answer: B
Clarification: Parts of a cell called cell organelles deteriorate if isolated from the whole cell and hence they cannot be cultured in vitro. Whole cells on the other hand can be cultured in a laboratory.

2. The first culture of human cells began in ________
A. 1851
B. 1951
C. 2000
D. 1780
Answer: B
Clarification: The first culture of human cells was performed by George and Martha Gey in 1951 at John Hopkins University in 1951. Henrietta Lacks donated these cells from her malignant tumor named – HeLa cells.

3. Which cells are found in the intestinal lining?
A. Neurons
B. Epithelial cells
C. Hepatocytes
D. RBCs
Answer: B
Clarification: Epithelial cells line the intestine and are responsible for the uptake and absorption of nutrients from the digestive tract. Microvilli are located at the apical end of these cells and mitochondria are located at the basal end.

4. Microvilli are composed of ____________
A. red blood cells
B. myosin
C. white blood cells
D. actin
Answer: D
Clarification: The microvilli facilitate absorption of nutrients and project outwards from the apical cell surface because of the presence of a skeleton made of filaments. These filaments are composed of the protein actin.

5. Which organelle is located at the basal end of epithelial cells lining the intestine?
A. Mitochondria
B. Nucleus
C. Golgi complex
D. Cilia
Answer: A
Clarification: Large numbers of mitochondria are located at the basal end of epithelial cells and they generate ATP (energy unit of a cell) that provides energy for membrane transport processes of the cell.

6. In cellular division, one cell gives rise to two daughter cells containing equal volume. However such a case of regular division is not observed in ________________
A. White blood cells
B. Liver cells
C. Oocytes
D. Red blood cells
Answer: C
Clarification: Oocytes undergo irregular cell division where one daughter cell retains nearly all the cytoplasm which is later fertilized by a sperm cell and gives rise to an embryo. The other cell only consists of half the genetic material and no cytoplasm.

7. Light energy is converted to chemical energy by photosynthesis and is stored in________________
A. Glial cells
B. Mitochondria
C. Proteins
D. Carbohydrates
Answer: D
Clarification: The light energy which is converted to chemical energy by the photosynthetic pigments present in plant cells is stored in energy-rich carbohydrates like sucrose and starch.

8. In humans, glucose in the body is released by _____________
A. Intestine
B. Kidney
C. Liver
D. Lungs
Answer: C
Clarification: Glucose is released by liver into the blood stream which circulates throughout the body delivering chemical energy to all the cells of the body. This energy is stored in the form of ATP.

9. The sum total of all the chemical reactions taking place inside the cell, represent the cell’s _______________
A. Metabolism
B. Catabolism
C. Anabolism
D. Regulation
Answer: A
Clarification: All the chemical reactions that take place inside the cell represent the cell’s metabolism. Nearly all chemical reactions involved in the metabolism require enzymes that help pace up these reactions.

10. Motor proteins help in regulation which activities in a cell?
A. Mechanical
B. Chemical
C. Uptake
D. Regulation
Answer: A
Clarification: Cells perform lot of bustling activities in their daily discourse. This requires a lot of mechanical activities, regulation, uptake etc. The motor protein is one class of proteins amongst many that help in the mechanical activities of the cell.

11. German embryologist, Hans Driesch used which organism’s embryo in his studies?
A. Star-fish
B. Sea-urchin
C. Whale
D. Monkey
Answer: B
Clarification: In his studies, Hans Driesch used sea urchin’s embryo and found that first two or four cells could be isolated and can lead individually lead to the formation of complete new embryo.

12. Which are the two most important macromolecules of a cell?
A. Protein, carbohydrates
B. Protein, mitochondria
C. Protein, nucleus
D. Protein, membrane
Answer: C
Clarification: Proteins and nucleus are the most important macromolecules found in a living cell. All the regulation is done by the nucleus of the cell which harbors genetic code. Proteins on the other hand are necessary in the metabolism that takes place inside a cell.

Cell Biology Multiple Choice Questions on “Metabolism”.

1. Catabolic pathways result in _______________ of the molecules.
A. assembly
B. functionalization
C. conformation
D. disassembly
Answer: D
Clarification: Catabolism refers to the disassembly of complex molecules to form simpler products. Catabolism hence serves two roles: providing raw materials for synthesis of products and making chemical energy available for survival of a cell.

2. Energy released by catabolic pathways is stored in how many forms?
A. 1
B. 2
C. 3
D. 4
Answer: B
Clarification: Energy released by catabolic pathways is stored primarily in two forms: high energy phosphates like adenosine triphosphate and high energy electrons (NADPH).

3. Anabolic pathways are energy-requiring.
A. True
B. False
Answer: A
Clarification: Anabolic pathways lead to the formation of complex molecules from simpler raw products. These require chemical energy which is supplied by the exergonic catabolic pathways.

4. How many molecules of ATP are formed per molecule of oxidation of glucose?
A. 12
B. 24
C. 36
D. 48
Answer: C
Clarification: The free energy released by complete oxidation of glucose is ΔG⁰’ = -686 kcal/mol; which is very large. The free energy required to convert ADP to ATP is relatively small ΔG⁰’ = +7.3 kcal/mol. Upto 36 molecules of ATP can be formed per molecule of glucose.

5. The TCA cycle occurs in which region of a prokaryotic cell?
A. cytosol
B. mitochondria
C. ribsomes
D. golgi complex
Answer: A
Clarification: There are two stages in the catabolism of glucose namely glycolysis which occurs in the cytosol and tricarboxylic acid (TCA. cycle which occurs in the cytosol of prokaryotes and mitochondria of eukaryotes.

6. Glycolysis begins with which of the following reactions?
A. reduction
B. oxidation
C. phosphorylation
D. acidification
Answer: C
Clarification: Glycolysis begins with the addition of a sugar molecule to a phosphate group. Phosphorylation activates the sugar molecule to take part in later steps of the process and also reduce the concentration of glucose in the cytoplasm, promoting continued diffusion from blood to the cell.

7. NAD is a _________
A. enzyme
B. cofactor
C. protein
D. nucleoside
Answer: B
Clarification: Nicotinamide adenine dinucleotide is a non-protein cofactor called coenzyme. NAD plays a key role in the metabolism of the cell by donating and accepting electrons.

8. NAD⁺ can be derived from which vitamin?
A. A
B. C
C. Riboflavin
D. Niacin
Answer: D
Clarification: NAD⁺ is the reduced state of the coenzyme NAD. It is derived from the vitamin niacin and is loosely bound to the enzyme dehydrogenase.

9. In fermentation, which of the following is regenerated?
A. Starch
B. Oxygen
C. NAD⁺
D. NADH
Answer: C
Clarification: Cells are able to regenerate NAD⁺ by fermentation. In this process the transfer of electrons take place from NADH to pyruvate or to a compound derived from pyruvate.

10. In case of repeated contraction, muscle cells regenerate NAD⁺ by converting pyruvate to _____________
A. glycogen
B. lactate
C. starch
D. cellulose
Answer: B
Clarification: In case of repeated contraction, the oxygen levels drop down and make it difficult to keep up with the cell’s metabolic demands. Under these conditions, skeletal muscle cells regenerate NAD⁺ by converting pyruvate to lactate.

11. Yeast cells convert pyruvate to lactate.
A. True
B. False
Answer: B
Clarification: Unlike the cells of skeletal muscles, which convert pyruvate to lactate in case of low oxygen supply; the yeast cells convert pyruvate to ethanol.

12. A cell’s reservoir of NADPH represents its _______________
A. oxidation state
B. oxidation power
C. tensile strength
D. reducing power
Answer: D
Clarification: A cell’s reservoir of NADPH is a measure of its reducing power and the usable energy. NADPH is a compound similar to NADH but with an additional phosphate group.

13. How many mechanisms exist for altering the shape of an enzyme, playing a role in regulating glucose oxidation?
A. 1
B. 2
C. 3
D. 4
Answer: B
Clarification: For regulating glucose oxidation, there are two mechanisms that are responsible for altering the shape of an enzyme’s active site namely covalent modification and allosteric modification.

14. Protein kinases are responsible for transferring which group?
A. oxygen
B. carbon
C. amino
D. phosphate
Answer: D
Clarification: Protein kinases are a class of enzymes that transfer phosphate group to other proteins (covalent modification). These are hence vital in hormone action, cell division and gene expression.

15. How many types of protein kinases are there?
A. 1
B. 2
C. 3
D. 4
Answer: B
Clarification: There are two types of protein kinases: one adds phosphate group to tyrosine residues in a protein and the other adds phosphate group to serine or threonine residues.

Cell Biology Multiple Choice Questions on “Mitochondrial Structure and Function – 1”.

1. Mitochondria is the organ for ______
A. Cellular respiration
B. Cellular digestion
C. Cellular death
D. Cellular motility
Answer: A
Clarification: Mitochondria is a bean shaped organ in the cell cytoplasm. Its major role is cellular respiration. It utilizes oxygen and carbohydrate to release carbon dioxide and energy in the form of ATP. Cellular respiratory processes such as Kreb’s cycle and oxidative phosphorylation takes place in mitochondria.

2. The protruding invaginated sheets inside mitochondria is known as _____
A. Cristae
B. Fimbrae
C. Hyphae
D. Cellular Digestion
Answer: A
Clarification: The structure of mitochondria under the microscope is bean shaped with inner and outer mitochondrial membranes surrounding it. The inner membrane invaginates inside to produce finger-like protrusions known as the Cristae.

3. The inner boundary membrane and inner cristal membrane are joined by ____
A. Mitochondrial junctions
B. Membrane junctions
C. Cristae junctions
D. Tubule junctions
Answer: C
Clarification: The inner boundary membrane and internal cristal membranes in the mitochondria are joined to one another by narrow tubular connections known as cristae junctions. The cristae are internal protrusions that hold the respiratory mechanism important for cellular respiration.

4. Which part of mitochondria has almost 70-75% protein content?
A. Outer membrane
B. Inner membrane
C. Both outer and inner membrane
D. Intermembrane space
Answer: B
Clarification: The outer membrane of mitochondria is composed of approximately 50% lipid by weight and contains a mixture of different enzymes. The inner membrane contains more than 100 different polypeptides and has a very high protein to lipid ratio. The protein content exceeds 70% by weight.

5. Which part of mitochondria is responsible for the degradation of many enzymes?
A. Mitochondrial matrix
B. Cristae
C. Inner membrane
D. Outer membrane
Answer: D
Clarification: The outer membrane of mitochondria is composed of approximately 50% lipid by weight and contains a mixture of different enzymes. It is involved in diverse activities such as enzyme degradation. The oxidation of epinephrine, degradation of tryptophan and elongation of fatty acid takes place in outer mitochondrial membrane.

6. In the inner membrane of mitochondria, there is one protein molecule for approximately every _______
A. 15 phospholipids
B. 25 phospholipids
C. 5 phospholipids
D. 10 phospholipids
Answer: A
Clarification: The inner membrane contains more than 100 different polypeptides and has a very high protein to lipid ratio. The protein content exceeds 70% by weight. This corresponds to about one protein molecule for every 15 phospholipids.

7. Cardiolipin present in inner mitochondrial membrane plays a role in ___________
A. Formation of the respiratory mechanisms
B. Activation of proteins involved in Glycolysis
C. Activation of proteins involved in electron oxidation
D. Activation of proteins
Answer: C
Clarification: The inner membrane of mitochondria is virtually devoid of cholesterol and rich in unusual phospholipid and cardiolipins, which is the characteristics of bacterial membrane, from which the inner mitochondrial membrane has presumable evolved. Cardiolipin plays a role in facilitating the activity of several large protein complexes involved in lector transport and ATP synthesis.

8. Porins are present in ____________
A. Inner membrane
B. Outer membrane
C. Both inner and outer membrane
D. Intermembrane space
Answer: C
Clarification: Porins are integral proteins that have relatively large internal channel surrounded by a barrel of Beta strands. The porins of outer mitochondrial membrane are dynamic structures that are more permeable to molecules such as ATP, NAD and Coenzyme A. The inner mitochondrial membrane is highly impermeable and all molecules and ions require special membrane transporters to gain entrance.

9. The mitochondrial DNA in humans encode for how many poplypeptides?
A. 15
B. 13
C. 12
D. 11
Answer: B
Clarification: The mitochondria possess their own genetic material and the machinery to manufacture their own RNAs and proteins. The mitochondrial DNA encodes a small number of polypeptides which are 13 in humans. These are tightly integrated in the inner mitochondrial membrane along with polypeptides encoded by nuclear genes.

10. Human mitochondrial DNA encodes for ____________
A. 2 rRNAs
B. 3 rRNAs
C. 1 rRNA
D. 4 rRNAs
Answer: A
Clarification: The mitochondria possess their own genetic material and the machinery to manufacture their own RNAs and proteins. In humans, the mitochondrial DNA encodes for 2 ribosomal RNAs (rRNAs).

11. Human mitochondrial DNA encodes for _________
A. 21 tRNAs
B. 31 tRNAs
C. 22 tRNA
D. 24 tRNAs
Answer: C
Clarification: The mitochondria possess their own genetic material and the machinery to manufacture their own RNAs and proteins. In humans, the mitochondrial DNA encodes for 2 ribosomal RNAs (rRNAs) and also 22 transfer RNAs (tRNAs) that are used in protein synthesis within the organelle.

12. The mitochondrial RNA polymerase is made up of _____________
A. 1 subunit
B. 2 subunits
C. 3 subunits
D. multiple subunits
Answer: A
Clarification: Mitochondrial RNA polymerase helps in the synthesis of proteins from mitochondrial RNA. The mitochondrial RNA polymerase is unlike the multi-subunit RNA polymerase enzyme of prokaryotic and eukaryotic cell and contains only a single subunit similar to certain bacterial viruses.