Selected MCQ

Current Question
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 1
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.
Related Question 2
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 3
A mutation prevents dynein from binding microtubules in eukaryotic cells. Which of the following processes would be most directly impaired?
  • A. Skeletal muscle contraction
  • B. Movement of vesicles from the Golgi apparatus to the endoplasmic reticulum
  • C. Movement of chromosomes toward the spindle poles during mitosis
  • D. Sliding of microtubule doublets in eukaryotic cilia and flagella
Correct Answer: D
Explanation:
Dynein motor proteins drive the sliding of microtubule doublets in cilia and flagella. Without functional dynein, ciliary and flagellar motion would be impaired. (Other processes involve myosin or different motor proteins.)
Related Question 4
Where in the nucleus are ribosomal RNAs transcribed in eukaryotic cells?
  • A. Nucleolus
  • B. Euchromatin
  • C. Chromatin loops
  • D. Nuclear lamina
Correct Answer: A
Explanation:
The nucleolus is the site of rRNA gene transcription (by RNA Pol I) and ribosome assembly.
Related Question 5
A red blood cell (internal osmolarity ~290 mOsm) is placed in a 100 mM NaCl solution (assume full dissociation). Which best describes the movement of water?
  • A. The cell loses water and shrinks
  • B. The cell gains water and swells
  • C. No net water movement
  • D. The cell bursts immediately
Correct Answer: B
Explanation:
100 mM NaCl yields ~200 mOsm outside (hypotonic to the cell). Water enters the cell, causing it to swell.