Selected MCQ

Current Question
During agarose gel electrophoresis of DNA, in which direction do DNA fragments migrate?
  • A. Toward the cathode (negative electrode)
  • B. Toward the anode (positive electrode)
  • C. DNA does not migrate in agarose
  • D. Toward the North Pole
Correct Answer: B
Explanation:
DNA has a negative charge (due to phosphate groups) and migrates toward the positively charged electrode (anode) when an electric field is applied.
Related Question 1
Alternative splicing occurs during gene expression at the level of:
  • A. DNA replication
  • B. Transcription initiation
  • C. Pre-mRNA processing (RNA splicing)
  • D. Protein folding
Correct Answer: C
Explanation:
Alternative splicing of pre-mRNA allows different exons to be joined or skipped, producing multiple mRNA variants from one gene during RNA processing.
Related Question 2
Which of the following is NOT typically controlled during industrial fermentation in a bioreactor?
  • A. Temperature
  • B. pH
  • C. Oxygen concentration
  • D. DNA sequence of the microorganism
Correct Answer: D
Explanation:
A, B, and C (temperature, pH, oxygen) are critical parameters controlled in fermentation. The chosen strain fixes the DNA sequence and is not a controlled parameter during the run.
Related Question 3
On which end of a tRNA molecule is the amino acid attached during translation?
  • A. 5′ end
  • B. 3′ end
  • C. D-loop
  • D. Anticodon loop
Correct Answer: B
Explanation:
The 3′-terminal CCA sequence of tRNA is where aminoacyl-tRNA synthetases covalently attach the amino acid.
Related Question 4
During PCR, Taq DNA polymerase has an optimal extension temperature of approximately:
  • A. 50°C
  • B. 60°C
  • C. 72°C
  • D. 95°C
Correct Answer: C
Explanation:
Taq polymerase is most active at around 72°C, which is used for the extension step to synthesize new DNA strands.
Related Question 5
Why does the lagging strand of DNA require more DNA ligase activity during replication than the leading strand?
  • A. It contains more errors to fix
  • B. It is synthesized more continuously
  • C. It is synthesized discontinuously in Okazaki fragments
  • D. It is shorter than the leading strand
Correct Answer: C
Explanation:
The lagging strand is made in short Okazaki fragments, each of which must be joined by DNA ligase. The leading strand is continuous and requires minimal ligation.