Mock test 8

Mock Test 08: Mega Final Mix (60 Questions)

90:00

1. Which eukaryotic DNA polymerase possesses primase activity? A) Pol Alpha B) Pol Delta C) Pol Epsilon D) Pol Gamma

Ans: A. Pol Alpha acts as a primase to initiate DNA synthesis.

2. Rho-independent transcription termination in bacteria relies on: A) A rut site B) GC-rich hairpin followed by a poly-U tract C) ATP hydrolysis D) Sigma factor dissociation

Ans: B. The hairpin stalls the polymerase, and weak A-U bonds allow transcript release.

3. The Shine-Dalgarno sequence pairs with which component during translation initiation? A) 5S rRNA B) 16S rRNA C) 23S rRNA D) Initiator tRNA

Ans: B. It base-pairs with the 3' end of the 16S rRNA in the 30S subunit.

4. Which of the following histone modifications is generally associated with transcriptional activation? A) H3K9 methylation B) H3K27 methylation C) Histone acetylation D) DNA methylation

Ans: C. Acetylation neutralizes lysine's positive charge, relaxing chromatin.

5. Which snRNP is the catalytic core of the spliceosome? A) U1 B) U2 C) U6 D) U4

Ans: C. U6 base-pairs with U2 to form the active catalytic center.

6. The Ames test is used to determine: A) Protein concentration B) Mutagenic potential of a chemical C) DNA sequence D) Viral load

Ans: B. It uses Salmonella typhimurium strains to test for reverse mutations.

7. In the lac operon, the CAP-cAMP complex acts as a: A) Negative regulator B) Positive regulator C) Co-repressor D) Inducer

Ans: B. It binds upstream of the promoter to enhance RNA polymerase binding.

8. Telomeres are synthesized by a ribonucleoprotein that functions as a: A) DNA-dependent RNA polymerase B) Reverse transcriptase C) Endonuclease D) Ligase

Ans: B. Telomerase uses its own RNA template to synthesize DNA (Reverse transcription).

9. Which initiation factor prevents the premature association of the 30S and 50S ribosomal subunits? A) IF-1 B) IF-2 C) IF-3 D) EF-Tu

Ans: C. IF-3 binds the 30S subunit to keep it separated from the 50S subunit.

10. The PAM sequence is crucial for the function of: A) Restriction enzymes B) CRISPR-Cas9 C) Zinc Finger Nucleases D) TALENs

Ans: B. Protospacer Adjacent Motif (PAM) is required for Cas9 to bind and cut target DNA.

11. In uncompetitive inhibition, the Lineweaver-Burk plot shows lines that are: A) Intersecting at the Y-axis B) Intersecting at the X-axis C) Parallel D) Non-linear

Ans: C. Both Vmax and Km decrease proportionately, yielding parallel lines.

12. Trypsin specifically cleaves peptide bonds at the carboxyl side of: A) Basic amino acids (Lys, Arg) B) Aromatic amino acids (Phe, Trp, Tyr) C) Small uncharged amino acids (Gly, Ala) D) Acidic amino acids (Asp, Glu)

Ans: A. Trypsin targets positively charged/basic residues.

13. The Bohr effect states that hemoglobin's oxygen affinity decreases when: A) pH increases B) CO2 decreases C) pH decreases D) O2 concentration is high

Ans: C. Lower pH (high H+) and high CO2 stabilize the T-state, promoting O2 release.

14. Which amino acid is an alpha-helix breaker due to its cyclic structure? A) Glycine B) Proline C) Histidine D) Tryptophan

Ans: B. Proline lacks an amide hydrogen to participate in H-bonding and introduces a kink.

15. The catalytic triad of serine proteases (like Chymotrypsin) consists of: A) Ser, His, Asp B) Ser, Cys, Glu C) Thr, His, Asp D) Ser, Lys, Arg

Ans: A. Serine, Histidine, and Aspartate form the classic triad.

16. What is the isoelectric point (pI) of an amino acid with pK1=2.3 and pK2=9.7 (no ionizable R group)? A) 7.0 B) 6.0 C) 12.0 D) 4.0

Ans: B. pI = (2.3 + 9.7) / 2 = 6.0.

17. A non-competitive inhibitor alters which kinetic parameter? A) Increases Km B) Decreases Vmax C) Decreases Km D) Increases Vmax

Ans: B. It binds to an allosteric site regardless of substrate binding, lowering functional enzyme concentration (Vmax).

18. The Hill coefficient (n) for an enzyme is 1.5. This indicates: A) No cooperativity B) Negative cooperativity C) Positive cooperativity D) Competitive inhibition

Ans: C. n > 1 indicates positive cooperativity (e.g., hemoglobin).

19. Which test detects the presence of peptide bonds? A) Benedict's test B) Biuret test C) Ninhydrin test D) Iodine test

Ans: B. The Biuret test yields a purple color in the presence of peptide bonds.

20. What disease is caused by misfolding of the PrP protein from alpha-helices to beta-sheets? A) Alzheimer's B) Huntington's C) Prion diseases (e.g., CJD) D) Parkinson's

Ans: C. Prions propagate by transmitting a misfolded state.

21. The rate-limiting enzyme of Glycolysis is: A) Hexokinase B) Pyruvate Kinase C) Phosphofructokinase-1 (PFK-1) D) Aldolase

Ans: C. PFK-1 is the most critical regulatory step in glycolysis.

22. Which coenzymes are required by the Pyruvate Dehydrogenase complex? A) TPP, Lipoic acid, FAD, NAD+, CoA B) PLP, Biotin, FAD, NAD+, CoA C) TPP, Biotin, NADPH, CoA, ATP D) Lipoic acid, PLP, FAD, NADP+, ATP

Ans: A. These five are essential for the oxidative decarboxylation of pyruvate.

23. In the TCA cycle, FADH2 is produced during the conversion of: A) Citrate to Isocitrate B) Succinate to Fumarate C) Malate to Oxaloacetate D) Alpha-ketoglutarate to Succinyl-CoA

Ans: B. Catalyzed by Succinate Dehydrogenase (Complex II).

24. What drives the synthesis of ATP in oxidative phosphorylation? A) Electron transfer to oxygen B) Proton motive force (PMF) C) Substrate-level phosphorylation D) Hydrolysis of GTP

Ans: B. The proton gradient created across the inner mitochondrial membrane drives ATP synthase.

25. Fatty acid synthesis occurs in the: A) Mitochondria B) Endoplasmic reticulum C) Cytosol D) Lysosome

Ans: C. Beta-oxidation happens in the mitochondria, but synthesis happens in the cytosol.

26. Which enzyme bypasses Pyruvate Kinase in gluconeogenesis? A) Pyruvate carboxylase and PEPCK B) Fructose-1,6-bisphosphatase C) Glucose-6-phosphatase D) Malic enzyme

Ans: A. Pyruvate is converted to Oxaloacetate (via PC), then to Phosphoenolpyruvate (via PEPCK).

27. The first committed step of the Pentose Phosphate Pathway is catalyzed by: A) Transketolase B) Transaldolase C) Glucose-6-phosphate dehydrogenase D) Phosphopentose isomerase

Ans: C. G6PD is the primary regulatory point producing NADPH.

28. Which of the following is NOT a ketone body? A) Acetoacetate B) Acetone C) Beta-hydroxybutyrate D) Acetyl-CoA

Ans: D. Acetyl-CoA is the precursor to ketone bodies, not a ketone body itself.

29. In the Urea cycle, argininosuccinate is cleaved into arginine and: A) Fumarate B) Malate C) Oxaloacetate D) Citrulline

Ans: A. Argininosuccinate lyase produces Arginine and Fumarate (which links to the TCA cycle).

30. Dinitrophenol (DNP) affects oxidative phosphorylation by: A) Inhibiting Complex IV B) Inhibiting ATP synthase C) Uncoupling proton gradient from ATP synthesis D) Blocking electron transport at Complex I

Ans: C. DNP carries protons across the membrane, dissipating the gradient as heat.

31. In Agrobacterium-mediated plant transformation, which vir gene acts as an endonuclease to nick the T-DNA? A) virA B) virG C) virD1/D2 D) virE2

Ans: C. VirD1/D2 complex recognizes border sequences and cuts the DNA.

32. Elicitation using metal nanoparticles in plant tissue culture is primarily used to stimulate the production of: A) Primary metabolites B) Secondary metabolites C) Chlorophyll D) Cellulose

Ans: B. Nanoparticles act as elicitors, triggering oxidative stress responses that drastically increase secondary metabolite yields.

33. The Shikimate pathway is crucial in plants for the synthesis of: A) Aliphatic amino acids B) Aromatic amino acids C) Fatty acids D) Sterols

Ans: B. It produces Phe, Tyr, and Trp, which are precursors for many secondary metabolites.

34. Protoplast fusion requires the removal of the plant cell wall using: A) Pectinase and Cellulase B) Amylase and Lipase C) Protease and Nuclease D) Chitinase and Lysozyme

Ans: A. These enzymes degrade the pectin and cellulose of the cell wall.

35. In GPCR signaling, Adenylyl Cyclase catalyzes the conversion of ATP into: A) IP3 B) DAG C) cAMP D) cGMP

Ans: C. Cyclic AMP (cAMP) is the secondary messenger activated by Gs proteins.

36. Which protein targets other proteins for proteasomal degradation? A) Ubiquitin B) Clathrin C) Chaperonin D) Caspase

Ans: A. Polyubiquitination tags proteins for destruction by the 26S proteasome.

37. The Retinoblastoma (Rb) protein halts the cell cycle at which checkpoint? A) G2/M B) G1/S C) Metaphase/Anaphase D) S/G2

Ans: B. It binds E2F, preventing progression into the S phase until phosphorylated by CDKs.

38. Cytochrome c release from the mitochondria triggers which pathway? A) Extrinsic Apoptosis B) Intrinsic Apoptosis C) Necrosis D) Autophagy

Ans: B. It forms the apoptosome with Apaf-1, initiating intrinsic apoptosis.

39. SNARE proteins are essential for: A) Vesicle fusion with target membranes B) DNA supercoiling C) Chromosome segregation D) Actin polymerization

Ans: A. v-SNAREs and t-SNAREs interact to fuse vesicles with membranes.

40. In C4 plants, the primary acceptor of CO2 in mesophyll cells is: A) RuBP B) Phosphoenolpyruvate (PEP) C) Oxaloacetate D) Malate

Ans: B. PEP carboxylase fixes CO2 to PEP forming Oxaloacetate.

41. Which class of antibodies is the most abundant in mucosal secretions? A) IgG B) IgM C) IgA D) IgE

Ans: C. Secretory IgA protects mucosal surfaces.

42. MHC Class I molecules present antigens to: A) CD4+ Helper T Cells B) CD8+ Cytotoxic T Cells C) B Cells D) Macrophages

Ans: B. MHC I binds CD8+ T cells (endogenous antigens).

43. V(D)J recombination occurs in: A) Bone marrow and Thymus B) Lymph nodes C) Spleen D) Blood stream

Ans: A. It happens during primary lymphocyte maturation in generative organs.

44. Monoclonal antibodies are typically produced using: A) PCR B) Hybridoma technology C) Recombinant E. coli D) Phage display only

Ans: B. Fusing a B-cell with a myeloma cell creates an immortal hybridoma.

45. In Mendelian genetics, a 9:3:4 phenotypic ratio in the F2 generation indicates: A) Incomplete dominance B) Codominance C) Recessive epistasis D) Dominant epistasis

Ans: C. Recessive epistasis modifies the classic 9:3:3:1 ratio.

46. The Hardy-Weinberg principle states that allele frequencies remain constant if: A) Mutations occur frequently B) Mating is random C) Population size is small D) Natural selection is strong

Ans: B. HW equilibrium requires random mating, large population, no mutations, no drift, no selection.

47. A Lod score of 3.0 indicates that linkage is: A) 1000 times more likely than independent assortment B) 3 times more likely C) 300 times more likely D) Impossible

Ans: A. Lod score = log10(Odds). A score of 3 means 10^3 = 1000:1 odds of linkage.

48. Klinefelter syndrome is genetically defined as: A) 45, XO B) 47, XXY C) 47, XYY D) 46, XY

Ans: B. Males with an extra X chromosome.

49. The classical complement pathway is initiated by: A) C3b binding to microbial surfaces B) Mannose-binding lectin C) C1q binding to Antigen-Antibody complexes D) Factor B

Ans: C. The classical pathway relies on antibodies (IgG or IgM) bound to antigens.

50. Barbara McClintock discovered Transposons in: A) Drosophila B) E. coli C) Maize D) Yeast

Ans: C. "Jumping genes" were first identified in maize (Ac/Ds system).

51. In Gel Filtration (Size Exclusion) Chromatography, which proteins elute first? A) Smallest proteins B) Largest proteins C) Positively charged proteins D) Hydrophobic proteins

Ans: B. Large proteins cannot enter the pores and wash straight through the column.

52. SDS-PAGE separates proteins strictly on the basis of: A) Charge B) Shape C) Mass (Molecular Weight) D) Hydrophobicity

Ans: C. SDS denatures and coats proteins with a uniform negative charge, making mass the only variable.

53. Circular Dichroism (CD) spectroscopy is primarily used to determine a protein's: A) Primary sequence B) Secondary structure (Alpha helix/Beta sheet) C) Quaternary structure D) Mass

Ans: B. Differential absorption of left and right circularly polarized light reveals secondary structural elements.

54. In Sanger sequencing, chain termination is achieved by incorporating: A) dNTPs B) ddNTPs (Dideoxynucleotides) C) ATP D) RNA primers

Ans: B. ddNTPs lack the 3'-OH group required for the addition of the next nucleotide.

55. Surface Plasmon Resonance (SPR) is a technique utilized to measure: A) Protein crystallization B) Real-time biomolecular interactions and binding kinetics C) DNA sequence D) Cell sorting

Ans: B. SPR provides real-time kon and koff rates without labeling.

56. Which technique is used to amplify trace amounts of DNA? A) Northern Blot B) PCR (Polymerase Chain Reaction) C) Western Blot D) Flow cytometry

Ans: B. PCR exponentially amplifies target DNA sequences.

57. Flow cytometry combined with FACS is used to: A) Sort cells based on fluorescent markers B) Sequence RNA C) Determine protein crystal structures D) Visualize organelle ultrastructure

Ans: A. Fluorescence-Activated Cell Sorting isolates specific cell populations.

58. The Edman degradation method sequences proteins starting from the: A) C-terminus B) N-terminus C) Internal Methionine D) Disulfide bridges

Ans: B. Phenyl isothiocyanate (PITC) reacts with the N-terminal amino acid.

59. X-ray crystallography requires the macromolecule to be in: A) Liquid state B) Gaseous state C) Crystal lattice form D) Lyophilized powder

Ans: C. Regular arrangement in a crystal is needed to diffract X-rays effectively.

60. Which isotope is commonly used to radiolabel DNA in Southern blotting experiments? A) 35S B) 32P C) 14C D) 3H

Ans: B. Phosphorus-32 is incorporated into the phosphodiester backbone of the DNA probe.