Selected MCQ

Current Question
Sanger (dideoxy) sequencing terminates DNA chain elongation using:
  • A. Restriction enzymes
  • B. Dideoxynucleotides (ddNTPs)
  • C. RNA polymerase
  • D. DNA methyltransferases
Correct Answer: B
Explanation:
In Sanger sequencing, modified nucleotides (ddNTPs) lacking a 3′-OH terminate extension when incorporated, allowing determination of the DNA sequence by fragment lengths.
Related Question 1
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 2
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 3
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.
Related Question 4
The technique for producing monoclonal antibodies involves fusing a specific antibody-producing B cell with a myeloma cell (a cancer cell). This hybrid cell line is called a:
  • A. Bacteriophage
  • B. Hybridoma
  • C. Plasmid
  • D. Complement
Correct Answer: B
Explanation:
A hybridoma results from fusing a single B lymphocyte (which produces one antibody) with a myeloma cell, creating an immortal cell line that produces identical (monoclonal) antibodies.
Related Question 5
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).