Category: Life Sciences Objective Questions

Life Sciences Multiple Choice Questions on “Recombination”.

1. Rearrangement of DNA that involves the breakage and reunion of DNA is called___________
A. Replication
B. Recombination
C. Translation
D. Transcription
Answer: B
Clarification: Recombination is the process of rearrangement of DNA of breakage and reunion and it can change the genomic configuration.

2. Recombination is responsible for crossing-over during meiosis of eukaryotic cells.
A. True
B. False
Answer: A
Clarification: Recombination was first recognized as the process which is responsible for crossing over in the meiosis. It is a large scale rearrangement of DNA molecules.

3. Which of the following is NOT true about homologous recombination?
A. Exchange of homologous segments
B. Exchange takes place between two homologous DNA molecules
C. It is also termed as general recombination
D. It involves a direct exchange of sequences of DNA
Answer: D
Clarification: Homologous recombination involves a reciprocal exchange of sequences of DNA.

4. Which of the following is site specific recombination?
A. Modification
B. Transposition
C. Holiday junction
D. Retrotransposons
Answer:b
Clarification: Transposition is the process of recombination, which allows one DNA sequence to inserted in another without taking care of sequence homology.

5. Who proposed holiday model for homologous recombination?
A. Gobind Khurana
B. Louis Pasteur
C. Robin Holiday
D. Niels Bohr
Answer: C
Clarification: Robin Holiday in 1964, proposed an appealing scheme for recombination called holiday model or hetroduplex model.

6. Which of the following is NOT a recombination system?
A. RecBCD
B. RecE
C. RecF
D. DnaF
Answer: D
Clarification: Homologous recombination was first described in bacterial systems. The three different recombination systems are RecF, RecE, and RecBCD.

7. Name the phenomenon of allele replacement during recombination and DNA repair?
A. Replication
B. Mutation
C. Transversion
D. Gene conversion
Answer: D
Clarification: Gene conversion is the phenomenon of changing allele forms during recombination and DNA repair.

8. Name the protein, which is involved in homologous recombination in E.coli?
A. Topoisomerase
B. Gyrase
C. Helicase
D. RecBCD enzyme
Answer: D
Clarification: The three different recombination systems are RecF, RecE, and RecBCD. RecBCD is known as Exonuclease V and it has both helicase and nuclease activity.

.

Life Sciences Interview Questions and Answers focuses on “Enzymes – 2”.

1. Which of the following function is catalyzed by Racemases?
A. Removal of water
B. Intramolecular transfer of a functional group
C. Interconversion of L and D stereoisomers
D. Inversion of asymmetric carbon atom
Answer: C
Clarification: Racemases are the class of Isomerases which catalyzes the intramolecular rearrangement and interconvert L and D stereoisomers. Like racemases another isomerase which catalyzes the intramolecular transfer of functional group is mutases.

2. The zymogen is an inactive precursor of an active enzyme.
A. True
B. False
Answer: A
Clarification: Inactive precursor is first cleaved to form active enzyme and this inactive precursor is known as a zymogen. Many proteolytic enzymes are first synthesized as an inactive precursor which further cleaved to form the active enzyme.

3. Which of the following is an example of ligases enzyme?
A. Mutases
B. Epimerases
C. Racemases
D. Carboxylases
Answer: D
Clarification: Carboxylases are the example of ligases enzyme. Ligases are the class of enzyme which deals with the formation of C-C, C-S, C-O and C-N bonds.

4. What is the binding energy?
A. Free energy released in the formation of enzyme-substrate interaction
B. The energy required to form a bond
C. The energy required to bind substrate
D. It is the activation energy
Answer: A
Clarification: Binding energy is the free energy released when the enzyme-substrate complex is formed. This energy is used to lessen the activation energy. Binding energy can be maximum when the only correct substrate binds to the enzyme.

5. Which of the following is INCORRECT for the lock-and-key model?
A. It is used to describe the binding process
B. The active site of the enzyme is complementary to the substrate
C. It demonstrates enzyme-substrate complex
D. The binding of the substrate produces a conformational change in enzyme
Answer: D
Clarification: Lock-and-key model is used to describe the enzyme-substrate complex. It is the binding process where the active site of an enzyme is complementary to the shape of the substrate. The binding of the substrate produces a conformational change in the enzyme is incorrect as the confirmation of enzyme changes only in the induced fit model.

6. Which of the following is not a catalytic strategy for an enzyme to perform specific reaction?
A. Covalent catalysis
B. Metal ion catalysis
C. Michaelis constant
D. Acid-base catalysis
Answer: C
Clarification: Enzymes involves more than one strategies to catalyze specific reactions. Acid-base catalysis, metal ion catalysis, and covalent catalysis are best-characterized mechanisms employed by an enzyme.

7. What is the SI unit of enzyme activity?
A. Km
B. Kat
C. K_cat
D. V_max
Answer: B
Clarification: Kat stands for katal, SI unit of enzyme activity. One katal is equals to the amount of enzyme that catalyzes the transformation of 1 mole of substrate per second. 1 katal = 1 mol sec^-1.

8. Which of the following is not an example of irreversible enzyme inhibitor?
A. Cyanide
B. Sarin
C. Diisopropyl phosphoflouridate (DIPF)
D. Statin drugs
Answer: D
Clarification: Irreversible inhibitor binds to the active site of the enzyme and destroys the functional group. These inhibitors are mostly toxic in nature. Statin drugs are the example of competitive inhibitors which is used to control cholesterol.

9. Lineweaver-Burk plot is also known as______
A. Double reciprocal plot
B. Hanes-Woolf plot
C. Eadie-Hofstee plot
D. Steady-state equation
Answer: A
Clarification: Lineweaver-Burk plot is a double reciprocal plot as it is the reciprocal of Michaelis-Menten equation represented in the graphical form.
1/V = Km/V_max [S] + 1/V_max.

10. Name the enzyme which is found in tears, sweat, and an egg white?
A. Ribozyme
B. Lysozyme
C. Zymogen
D. Isozymes
Answer: B
Clarification: Lysozyme is an enzyme which is present in secretions such as tears, sweat and found in egg white. Lysozyme cleaves the glycosidic bond that connects NAG and NAM of peptidoglycan cell wall.

11. What is an Isozyme?
A. Same structure, different function
B. Different structure, the same function
C. Same structure, the same function
D. Different structure, different function
Answer: B
Clarification: Isozymes are multiple forms of enzymes that have the same functions but differ in structure. For example, lactate dehydrogenase which catalyzes the conversion of pyruvate to lactate, it has five isoenzymes.

To practice all areas of Life Sciences for Interviews, .

This set of Life Sciences Multiple Choice Questions on “Lysosome”.

1. Which of the following organelle control intracellular digestion of macromolecules with the help of hydrolytic enzymes?
A. Plastid
B. Peroxisome
C. Lysosome
D. Actin
Answer: C
Clarification: Lysosomes are membrane-bound compartment filled with hydrolytic enzymes which control intracellular digestion in the macromolecules. It contains about 40 types of different hydrolytic enzymes.

2. pH of the lysosome is acidic in nature.
A. True
B. False
Answer: A
Clarification: The acidic nature of lysosome is maintained by a hydrogen pump in the lysosomal membrane which pumps hydrogen ion into lysosome and maintains pH of about 5.0 in its interior.

3. Which of these are not the hydrolytic enzymes of lysosome?
A. Lipases
B. Sulfatases
C. Phosphatases
D. Aldolase
Answer: D
Clarification: Lysosomes contain 40 types of hydrolytic enzymes which include lipases, sulphatases, phosphatases, glycosidases etc. These enzymes work optimally in the acidic environment and the lysosome provides an acidic environment for these enzymes.

4. Digestion of cell’s own component is known as__________
A. Autophagy
B. Heterophagy
C. Phagocytosis
D. Pinocytosis
Answer: A
Clarification: Autophagy is the process of self-digestion, autophagic vacuoles contain cells own components, known as autophagosome which further fuse to the lysosome where digestion of components takes place.

5. What is amphisome?
A. Early endosome
B. Fusion of endosome and autophagosome
C. Vacuole
D. The bigger size of lysosome
Answer: B
Clarification: Amphisome is formed when autophagosome fused with the endosomes. This amphisome further fused with lysosome for digestion. It will result in the release of macromolecules into the cytosol.

6. The release of melanosomes from melanocytes is mediated by which of the following process?
A. Autophagy
B. Endocytosis
C. Exocytosis
D. Pinocytosis
Answer: C
Clarification: In the condition of stress, cell releases undigested content by exocytosis of lysosomes. It is a minor pathway. Melanocyte in skin stores its pigment in lysosomes which releases it into the extracellular space of the epidermis.

7. Name the single membrane which surrounded the vacuoles?
A. Contractile vacuole
B. Meninges
C. Tonoplast
D. Sarcolemma
Answer: C
Clarification: Vacuoles are large, fluid-filled vesicles, present in most of the plants and fungal cells. These are surrounded by a single-membrane called tonoplast.

8. Which of the following organelle works as a lysosome in the plants?
A. Contractile vacuole
B. Peroxisome
C. Plastid
D. Vacuole
Answer: D
Clarification: Like a lysosome in animal cells, vacuoles are present in plants and fungi contain a variety of hydrolytic enzymes. The pH of vacuole is also acidic and is maintained by transport protein in the vacuolar membrane.

9. Which of the following pumps excess water out of the cell?
A. Contractile vacuole
B. Lysosome
C. Peroxisome
D. Vacuoles
Answer: A
Clarification: Contractile vacuole is different from vacuoles as it helps in osmoregulation. It is mainly found in protists and is used to pump excess water out of the cell.

.

Life Sciences Multiple Choice Questions on “B-Cell”.

1. Which of the following is responsible for B-cell activation?
A. Infection
B. Antibody
C. Antigen
D. Allergy
Answer: C
Clarification: The activation of mature B-cell is done by antigen. When antigen come in contact with B-cells, it undergoes clonal proliferation and divided into memory cells and plasma cells.

2. What is the meaning of thymus independent B-cell activation?
A. Without the participation of T-cell
B. Do not mature in the thymus
C. Thymus would not take part in its activation
D. Affinity maturation takes place in the thymus
Answer: A
Clarification: In thymus independent B-cell pathway, antigen activates B-cell without the participation of TH cell. Response generated by thymus independent antigens only generate IgM and do not give rise to memory.

3. Which of the following acts as a coreceptor for B-cell activation?
A. CD28
B. IL-2
C. IgA
D. CD19
Answer: D
Clarification: CD19, CD81, and CD21 are present on the B-cell membrane and known as a B-cell coreceptor. These receptors are used to determine a cell’s identity and for transducing signals.

4. Out of these, which transcription factor does not take part in B-cell activation?
A. Abl
B. NF- kB
C. Jun
D. Fos
Answer: A
Clarification: Transcription factors like NF-AT, CREB, JUN, FOS, and AP-1 promote gene expression required for B-cell proliferation into a plasma cell and the memory cell.

5. Hybridoma technology is used to produce___________
A. Interferons
B. Monoclonal antibodies
C. Antibodies
D. Immune response
Answer: B
Clarification: It is a method which is used for the production of hybridoma of B-cells. This hybridoma B-cell later used for the production of monoclonal antibodies. Monoclonal antibodies are highly specific against a single epitope of the antigen.

6. Name the drug which is used to isolate hybridoma cells from the media?
A. Amphetamine
B. Opium
C. Aminopterin
D. Cocaine
Answer: C
Clarification: Aminopterin inhibits dHFR enzyme and block denovo pathway of nucleotide synthesis, which further allow the survival of only hybridoma cells and B-cells in HAT media.

7. Name the most commonly used monoclonal antibody for treatment of breast cancer?
A. Bradikinins
B. Prostaglandin
C. Erbutir
D. Herceptin
Answer: D
Clarification: Monoclonal antibodies are specific against the particular antigen and these are used to treat the cancer as they release their toxins in the growing cells which interfere with their cellular processes. Herceptin is particularly for breast cancer while erbutir is for colorectal cancer.

8. Mark the one which is NOT used in generating antibody diversity?
A. Combinatorial V(D)J joining
B. Juntional and insertional diversification
C. Somatic hypermutation
D. Binary fission
Answer: D
Clarification: Different classes of antibodies have variable amino acid sequences at the N-terminal end which interacts with different types of antigens. Four theories have been proposed for generating antibody diversity.

9. Tolerance of self-antigen by B-cells are known as B-cell tolerance.
A. True
B. False
Answer: A
Clarification: Self tolerance is the process by which the immune system does not attack self antigen. Immunological tolerance of B-cell is called B-cell tolerance, B-cell produced by this process does not recognize self-antigen but may recognize non-self antigens.

.

Life Sciences Multiple Choice Questions on “DNA Repair”.

1. The correction of changes in DNA by a set of process known as___________
A. Replication
B. DNA repair
C. Translation
D. Transcription
Answer: B
Clarification: DNA repair is the correction process which is used to maintain genetic stability.

2. The genome can maintain its essential cellular function even without DNA repair.
A. True
B. False
Answer: B
Clarification: Genome cannot maintain its essential cellular function if the DNA is damaged. So, for the accurate functioning, a set of correction processes are used known as DNA repair.

3. Name the repair system for UV mediated damage of DNA?
A. Exchange of homologous segments
B. DNA glycosylase
C. Nucleotide excision repair
D. Photoreactivation
Answer: D
Clarification: Exposure to UV radiation can cause pyrimidine dimer which is repaired by a light dependent direct system called photoreactivation.

4. Which of the following enzyme is used in photoreactivation process?
A. DNA ligase
B. DNA photolyase
C. DNA polymerase
D. Primase
Answer: B
Clarification: DNA photolyase participates in the DNA repair system when the damage takes place by UV radiation.

5. Name the repair system which involves the removal of the damaged segment of DNA?
A. Recombinational repair
B. Direct repair
C. Excision repair
D. Mismatched repair
Answer: C
Clarification: Excision of the damaged site comes under the excision repair system. It is of two types, base excision repair and nucleotide excision repair.

6. Name the enzyme which initiates base excision repair process?
A. RNA polymerase
B. DNA polymerase
C. DNA photolyase
D. DNA glycosylase
Answer: D
Clarification: DNA glycosylase cleaves N-glycosidic bonds which liberates altered base and generates apurinic or an apyrimidic site.

7. Which of the following enzyme works in the nucleotide excision repair?
A. DNA photolyase
B. ABC exinuclease
C. DNA glycosylase
D. RecA
Answer: B
Clarification: ABC excinuclease involves the removal of short, usually 12 nucleotide segment. This system is best studied in E.coli.

8. Mark the one, which is NOT a subunit of ABC exinuclease?
A. UvrA
B. UvrB
C. UvrC
D. UvrF
Answer: D
Clarification: ABC exinuclease binds at the site of lesion for the purpose of excision. It consists of three subunits i.e, UvrA, UvrB, and UvrC.

9. Which of the following is NOT the function of the enzyme systems involved in mismatch repair?
A. Recognize mismatched base pair
B. Gene conversion
C. Determine incorrect base from a mismatch
D. Excise incorrect base and carry out repair system
Answer: B
Clarification: Gene conversion is the phenomenon of changing allele forms during recombination and DNA repair.

10. Mark the one, which is CORRECT for SOS repair.
A. RecA protein participates
B. A free radical mechanism is involved
C. The repair enzyme functions only once
D. No bases or nucleotides are removed
Answer: A
Clarification: SOS repair involves RecA protein and is responsible for error prone replication. Final reaction is catalyzed by DNA ligase.

.

Life Sciences Multiple Choice Questions on “Bioenergetics”.

1. Law of thermodynamics which states that energy can neither be created nor be destroyed is ___________
A. The second law of thermodynamics
B. Third law of thermodynamics
C. First law of thermodynamics
D. Zero-order kinetics
Answer: C
Clarification: First law of thermodynamics depicts that energy can neither be created nor be destroyed but it can transform from one form to another. This shows that the energy remains constant in the system and in surroundings.

2. Gibb’s free energy is the portion of the total energy which is available for useful work.
A. True
B. False
Answer: A
Clarification: Gibb’s free energy is also known as chemical potential and is denoted by ∆G. It is the portion of total energy in a system which is available for work.

3. Which of the following equation shows the relationship between free energy change (∆G) and the change in entropy (∆S), under constant temperature and pressure?
A. ∆G = T∆H – ∆S
B. ∆G = T∆H/∆S
C. ∆G = ∆H/T∆S
D. ∆G = ∆H – T∆S
Answer: D
Clarification: The relationship between free energy change and change in entropy of a reacting system under constant temperature and pressure is given by equation ∆G = ∆H – T∆S, where ∆H is the change in enthalpy and T is temperature.

4. What is the value of ∆G, when a system is in equilibrium?
A. ∆G = 0
B. ∆G = 1
C. ∆G = -1
D. ∆G = ∆G֯
Answer: A
Clarification: Under equilibrium, both forward and reverse reactions occur at equal rates which make a change in free energy zero.

5. Which of the following factor is not responsible for the actual change in free energy (∆G)?
A. Temperature
B. Pressure
C. The initial concentration of reactant and products
D. pH
Answer: D
Clarification: During a reaction, the actual change in free energy is influenced by temperature, pressure, and the concentration of reactant and product at an initial level while ph does not affect the rate of reaction.

6. Which of the following equation gives the relationship between ∆G֯ and Keq?
A. ∆G֯ = -RT ln K_eq
B. ∆G֯ = ln K_eq
C. ∆G = ∆G֯ (-RT K_eq)
D. ∆G = -RT ln K_eq
Answer: A
Clarification: Equation ∆G֯ = -RT ln Keqis correct as Keq is the equilibrium constant, R is the gas constant and T is the absolute temperature. This equation shows the simple prediction about the rate of reaction as if it proceeds forward, reverse or is at equilibrium.

7. What is the standard free energy change of ATP?
A. Small and negative
B. Large and positive
C. Large and negative
D. Small and positive
Answer: C
Clarification: The phosphoryl transfer potential determines the negative free energy values. ATP has a higher tendency to transfer its terminal phosphoryl group to water during hydrolysis and generate large and negative free energy change.

8. Which of the following act as a storage form of high energy phosphate?
A. Glucose-6-phosphate
B. Phosphoenolpyruvate
C. Phosphagens
D. Glycerol phosphate
Answer: C
Clarification: High energy phosphate stored as the phosphagens. It is of two types, creatine phosphate in vertebrates and arginine phosphate in invertebrates. Phosphagens maintains the concentration of ATP when it is utilized as a source of energy.

9. What is the name of the molecule which donates its electrons?
A. Reducing agent
B. Oxidative agent
C. Standard reduction potential
D. Oxidant
Answer: A
Clarification: An electron-donating molecule in an oxidation-reduction reaction is called the reducing agent while an electron accepting molecule is called an oxidizing agent or oxidant.

10. What is reduction potential?
A. The molecule loses an electron
B. An atom/molecule gains an electron
C. Reducing the power of an electron
D. Oxidation power of an electron
Answer: B
Clarification: Reduction potential is the readiness with which a molecule gains an electron. It is calculated in volts (V). Electrons move more rapidly from less positive reduction potential to molecules having more reduction potential.

.