Selected MCQ

Current Question
Which statement correctly describes the role of nuclear pore complexes in eukaryotic cells?
  • A. They allow passive diffusion of all proteins smaller than ~100 kDa
  • B. They actively transport large molecules into and out of the nucleus
  • C. They separate the nuclear interior from the cytosol without any transport
  • D. They are the sites where rRNA is transcribed and processed
Correct Answer: B
Explanation:
Nuclear pore complexes selectively transport large molecules (such as mRNA and proteins with nuclear localization/export signals) between the nucleus and the cytoplasm. Small molecules can diffuse passively up to ~40 kDa.
Related Question 1
During the eukaryotic cell cycle, which checkpoint ensures that all chromosomes are correctly attached to the mitotic spindle before proceeding to anaphase?
  • A. G1/S checkpoint
  • B. G2/M checkpoint
  • C. Spindle (metaphase) checkpoint
  • D. S-phase checkpoint
Correct Answer: C
Explanation:
The spindle assembly (metaphase) checkpoint monitors attachment of all kinetochores to spindle microtubules. It prevents the onset of anaphase until all chromosomes are properly aligned and attached.
Related Question 2
Which of the following best describes clathrin function in eukaryotic cells?
  • A. It mediates the transport of proteins from the ER to the Golgi.
  • B. It forms a coat around vesicles during receptor-mediated endocytosis.
  • C. It phosphorylates tyrosine residues in signaling receptors.
  • D. It generates a proton gradient in endosomes.
Correct Answer: B
Explanation:
Clathrin polymerizes into a lattice on the inner surface of the plasma membrane, forming coated pits and vesicles that internalize receptors and ligands.
Related Question 3
The 5′ cap added to eukaryotic mRNAs is:
  • A. A string of adenine residues at the 5′ end
  • B. A modified guanosine (7-methylguanosine) linked 5′→5′
  • C. A poly-uridine sequence at the 3′ end
  • D. A phosphate group at the 5′ end
Correct Answer: B
Explanation:
The 5′ cap is a 7-methylguanosine joined via a 5′-to-5′ triphosphate linkage to the first nucleotide of the mRNA, protecting it from degradation and aiding translation.
Related Question 4
Which term describes genes that are located on the same chromosome and inherited together more often than by chance?
  • A. Linked genes
  • B. Epistatic genes
  • C. Polygenic genes
  • D. Independent genes
Correct Answer: A
Explanation:
Linked genes are near each other on the same chromosome. They tend to be inherited together, and their recombination frequency is less than 50%.
Related Question 5
Which of the following best describes polygenic inheritance?
  • A. One gene affects multiple traits (e.g., pleiotropy)
  • B. Many genes contribute to one trait (e.g., skin color)
  • C. A trait determined by genes only on the X chromosome
  • D. Inheritance of mitochondrial DNA
Correct Answer: B
Explanation:
Polygenic inheritance means multiple genes (often with additive effects) determine a single phenotype, such as height or skin color, producing continuous variation.