Selected MCQ

Current Question
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 1
Which plasmid-based technique is used to enrich and detect low-abundance mRNAs by reverse transcription into cDNA?
  • A. RFLP analysis
  • B. Northern blotting
  • C. RT-PCR (reverse-transcription PCR)
  • D. Affinity chromatography
Correct Answer: C
Explanation:
RT-PCR involves reverse-transcribing RNA to cDNA and then amplifying specific sequences by PCR. It is very sensitive for detecting low-abundance transcripts.
Related Question 2
Which assay would you use to detect and quantify a specific DNA sequence in a sample?
  • A. ELISA
  • B. Southern blot
  • C. Western blot
  • D. Gram staining
Correct Answer: B
Explanation:
A Southern blot uses a DNA probe to hybridize with a specific DNA sequence immobilized on a membrane, allowing detection of that sequence in the sample.
Related Question 3
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 4
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 5
Fluorescence in situ hybridization (FISH) is a technique used to:
  • A. Fragment DNA into smaller pieces
  • B. Visualize specific DNA or RNA sequences in cells or chromosomes using fluorescent probes
  • C. Measure protein concentration in solution
  • D. Separate DNA by size
Correct Answer: B
Explanation:
FISH uses fluorescently labeled probes that hybridize to specific DNA sequences on chromosomes or cells, allowing localization under a fluorescence microscope.