Selected MCQ

Current Question
In eukaryotic pre-mRNA splicing, which nucleotides are found at the 5′ and 3′ ends of most introns?
  • A. GU at 5′ and AG at 3′ ends
  • B. GA at both ends
  • C. AA at 5′ and TT at 3′ ends
  • D. CT at 5′ and TC at 3′ ends
Correct Answer: A
Explanation:
The consensus splice donor site at the 5′ end of introns is “GU,” and the splice acceptor site at the 3′ end is “AG” in most eukaryotic genes.
Related Question 1
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 2
A mutation prevents dynein from binding microtubules in eukaryotic cells. Which of the following processes would be most directly impaired?
  • A. Skeletal muscle contraction
  • B. Movement of vesicles from the Golgi apparatus to the endoplasmic reticulum
  • C. Movement of chromosomes toward the spindle poles during mitosis
  • D. Sliding of microtubule doublets in eukaryotic cilia and flagella
Correct Answer: D
Explanation:
Dynein motor proteins drive the sliding of microtubule doublets in cilia and flagella. Without functional dynein, ciliary and flagellar motion would be impaired. (Other processes involve myosin or different motor proteins.)
Related Question 3
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 4
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 5
In genomic imprinting, the expression of a gene depends on its parental origin. For example, only the paternally inherited allele of a certain gene is expressed. This is known as:
  • A. Epigenetic modification
  • B. Loss of heterozygosity
  • C. Imprinting
  • D. Mendelian inheritance
Correct Answer: C
Explanation:
Genomic imprinting is an epigenetic phenomenon where only one allele (maternal or paternal) is expressed, depending on the parent of origin, while the other is silenced.