Selected MCQ

Current Question
DNA polymerases proofread the newly synthesized DNA strand using which activity?
  • A. 5′→3′ exonuclease
  • B. 3′→5′ exonuclease
  • C. Primase activity
  • D. Helicase activity
Correct Answer: B
Explanation:
Many DNA polymerases have 3′→5′ exonuclease activity that excises incorrectly paired nucleotides immediately after incorporation (proofreading).
Related Question 1
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.
Related Question 2
A newly synthesized protein is destined for secretion outside the cell. Which sequence or signal will it most likely contain?
  • A. A hydrophobic transmembrane domain
  • B. A nuclear localization signal
  • C. A signal peptide at the N-terminus
  • D. A peroxisomal targeting signal at the C-terminus
Correct Answer: C
Explanation:
Secreted proteins typically have an N-terminal signal peptide that directs the ribosome to the ER for co-translational translocation into the secretory pathway.
Related Question 3
In gene therapy using a viral vector, what is a major concern related to using retroviruses?
  • A. They cannot infect human cells
  • B. They only integrate into mitochondrial DNA
  • C. Insertional mutagenesis by random integration into the host genome
  • D. They cannot carry large genes
Correct Answer: C
Explanation:
Retroviral vectors integrate randomly into the host genome, risking insertional mutagenesis (disrupting host genes), which can cause cancer or other issues.
Related Question 4
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 5
In Western blotting, proteins are typically detected using:
  • A. DNA probes
  • B. RNA probes
  • C. Enzyme-linked antibodies
  • D. Radioactive amino acids
Correct Answer: C
Explanation:
Western blot uses antibodies (often enzyme-linked) that bind specific proteins on the membrane, allowing visualization via a colorimetric or chemiluminescent reaction.