Selected MCQ

Current Question
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 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
Why is fetal bovine serum commonly added to cell culture media?
  • A. To buffer the pH
  • B. To provide growth factors and nutrients
  • C. To increase osmolarity
  • D. To act as an antibiotic
Correct Answer: B
Explanation:
Fetal bovine serum supplies a mix of growth factors, hormones, and nutrients that support cell growth and viability in culture.
Related Question 3
What is the sedimentation coefficient (S value) of a complete eukaryotic ribosome?
  • A. 70S
  • B. 80S
  • C. 90S
  • D. 100S
Correct Answer: B
Explanation:
A eukaryotic ribosome is 80S, composed of a 60S large subunit and a 40S small subunit (70S in bacteria).
Related Question 4
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 5
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.