Selected MCQ

Current Question
Prokaryotic mRNAs often encode multiple proteins on a single transcript. This feature is known as:
  • A. Monocistronic transcription
  • B. Polycistronic transcription
  • C. Post-transcriptional splicing
  • D. Alternative splicing
Correct Answer: B
Explanation:
Polycistronic mRNA contains several open reading frames, each encoding a different protein. This is common in bacteria (e.g., operons).
Related Question 1
Which mechanism allows a single eukaryotic gene to encode multiple protein isoforms?
  • A. Alternative splicing
  • B. Alternative sigma factors
  • C. Gene duplication
  • D. Horizontal gene transfer
Correct Answer: A
Explanation:
Alternative splicing of a pre-mRNA can include or exclude exons, yielding different mRNAs and thus different protein isoforms from one gene.
Related Question 2
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 3
The 5′ cap added to eukaryotic mRNAs is:
  • A. A string of adenine residues at the 5′ end
  • B. A modified guanosine (7-methylguanosine) linked 5′→5′
  • C. A poly-uridine sequence at the 3′ end
  • D. A phosphate group at the 5′ end
Correct Answer: B
Explanation:
The 5′ cap is a 7-methylguanosine joined via a 5′-to-5′ triphosphate linkage to the first nucleotide of the mRNA, protecting it from degradation and aiding translation.
Related Question 4
Which term describes genes that are located on the same chromosome and inherited together more often than by chance?
  • A. Linked genes
  • B. Epistatic genes
  • C. Polygenic genes
  • D. Independent genes
Correct Answer: A
Explanation:
Linked genes are near each other on the same chromosome. They tend to be inherited together, and their recombination frequency is less than 50%.
Related Question 5
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.