Selected MCQ

Current Question
Which DNA repair pathway primarily corrects UV-induced thymine dimers?
  • A. Base-excision repair
  • B. Nucleotide-excision repair
  • C. Mismatch repair
  • D. Non-homologous end joining
Correct Answer: B
Explanation:
Nucleotide-excision repair recognizes bulky lesions like thymine dimers from UV exposure and removes a short single-stranded DNA segment including the damage.
Related Question 1
Which chromatography technique separates proteins primarily based on size using a gel matrix?
  • A. Ion-exchange chromatography
  • B. Gel filtration (size-exclusion) chromatography
  • C. Affinity chromatography
  • D. Reverse-phase chromatography
Correct Answer: B
Explanation:
Gel filtration chromatography (size-exclusion) separates proteins by size: larger molecules elute first because they enter fewer pores in the matrix, while smaller molecules elute later.
Related Question 2
In flow cytometry, cells are labeled with fluorescent antibodies and passed in a stream through a laser. This technique primarily measures:
  • A. Cell size and internal complexity
  • B. DNA sequence variants
  • C. Protein structure by X-ray diffraction
  • D. Glycolytic activity
Correct Answer: A
Explanation:
Flow cytometry measures light scattering (size and granularity) and fluorescence from labeled markers, allowing rapid analysis of cell populations (size, complexity, marker expression).
Related Question 3
SDS-PAGE separates proteins primarily based on:
  • A. Charge only
  • B. Size (molecular weight)
  • C. Hydrophobicity
  • D. Isoelectric point
Correct Answer: B
Explanation:
SDS denatures proteins and coats them with a negative charge that is proportional to their length. In SDS-PAGE, proteins are separated by size; smaller proteins migrate faster.
Related Question 4
Enzyme-linked immunosorbent assay (ELISA) is primarily used to:
  • A. Measure DNA concentration
  • B. Detect specific proteins or antibodies by an enzyme-mediated color change
  • C. Visualize chromosomes under a microscope
  • D. Amplify RNA
Correct Answer: B
Explanation:
ELISA employs enzyme-linked antibodies. When the target antigen or antibody is present, a substrate is converted to a colored product, indicating a positive result.
Related Question 5
Small interfering RNAs (siRNAs) are primarily involved in which cellular process?
  • A. DNA replication
  • B. RNA interference (RNAi) leading to mRNA degradation
  • C. Protein synthesis
  • D. Glycolysis
Correct Answer: B
Explanation:
siRNAs guide the RNA-induced silencing complex (RISC) to complementary mRNA, causing its cleavage and degradation, a form of RNA interference.