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MCQ Practice

Biology MCQs

Release of cytochrome c from mitochondria into the cytosol leads to which cellular process?

  • A. Necrosis
  • B. Apoptosis
  • C. Autophagy
  • D. Mitosis
Explanation:
Cytosolic cytochrome c triggers formation of the apoptosome, leading to caspase activation and programmed cell death (apoptosis).

Overexpression of the Bcl-2 protein in a cell would most likely result in which effect?

  • A. Increased apoptosis
  • B. Enhanced autophagy
  • C. Resistance to apoptosis
  • D. Increased necrosis
Explanation:
Bcl-2 is an anti-apoptotic protein. Its overexpression makes cells more resistant to apoptotic signals, promoting cell survival.

Which of the following is a key executioner caspase in the apoptosis pathway?

  • A. Caspase-3
  • B. Caspase-8
  • C. Caspase-1
  • D. Caspase-9
Explanation:
Caspase-3 is an executioner caspase that cleaves various cellular substrates to carry out apoptosis. Caspase-8 and -9 are initiators.

Phospholipase C (PLC) activation results in the generation of which second messenger that releases Ca²⁺ from the endoplasmic reticulum?

  • A. cAMP
  • B. cGMP
  • C. IP₃
  • D. DAG
Explanation:
PLC cleaves PIP₂ into IP₃ and DAG. IP₃ diffuses to the ER, causing Ca²⁺ release, while DAG activates PKC.

Activation of a Gs protein-coupled receptor typically leads to stimulation of which enzyme to increase intracellular cAMP?

  • A. Protein kinase C
  • B. Adenylyl cyclase
  • C. Phosphodiesterase
  • D. Guanylyl cyclase
Explanation:
Gs α-subunit activates adenylyl cyclase, which converts ATP to cAMP, raising second-messenger levels.

Which type of endocytosis involves clathrin-coated pits and often requires receptor binding?

  • A. Phagocytosis
  • B. Pinocytosis
  • C. Receptor-mediated endocytosis
  • D. Exocytosis
Explanation:
Receptor-mediated endocytosis uses clathrin-coated vesicles. Specific ligands bind membrane receptors, concentrating them in coated pits for internalization.

The sodium-potassium pump (Na⁺/K⁺-ATPase) is an example of which type of membrane transport?

  • A. Passive diffusion
  • B. Facilitated diffusion
  • C. Primary active transport
  • D. Secondary active transport
Explanation:
Na⁺/K⁺-ATPase uses ATP directly to pump Na⁺ out and K⁺ in against their gradients, classifying it as primary active transport.

Which motor protein transports vesicles toward the plus end of microtubules (generally the cell periphery)?

  • A. Kinesin
  • B. Dynein
  • C. Myosin
  • D. Actin
Explanation:
Kinesin moves cargo anterogradely toward microtubule plus ends (cell periphery). Dynein moves cargo retrogradely (toward minus ends).

Crawling movement of cells (e.g., fibroblasts) primarily depends on the polymerization of which cytoskeletal component?

  • A. Microtubules
  • B. Intermediate filaments
  • C. Actin microfilaments
  • D. Centrioles
Explanation:
Lamellipodia and filopodia are actin-based protrusions. Actin polymerization at the leading edge drives cell crawling and motility.

Which of the following organelles is present in plant cells but absent in animal cells?

  • A. Peroxisome
  • B. Centrosome
  • C. Chloroplast
  • D. Golgi apparatus
Explanation:
Chloroplasts (sites of photosynthesis) are found in plant and algal cells but not in animal cells.