Selected MCQ

Current Question
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 1
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 2
A single gene mutation causes both phenylketonuria (affecting skin pigment) and neurological impairment. This phenomenon is called:
  • A. Epistasis
  • B. Pleiotropy
  • C. Codominance
  • D. Penetrance
Correct Answer: B
Explanation:
One gene affecting multiple, seemingly unrelated traits (e.g., PKU’s effects on pigment and brain) is pleiotropy.
Related Question 3
Which eukaryotic RNA polymerase transcribes tRNA genes?
  • A. RNA polymerase I
  • B. RNA polymerase II
  • C. RNA polymerase III
  • D. RNA polymerase IV
Correct Answer: C
Explanation:
RNA Pol III transcribes tRNAs and 5S rRNA. Pol I makes most rRNAs, and Pol II makes mRNA and some snRNAs.
Related Question 4
Which motor protein transports vesicles toward the plus end of microtubules (generally the cell periphery)?
  • A. Kinesin
  • B. Dynein
  • C. Myosin
  • D. Actin
Correct Answer: A
Explanation:
Kinesin moves cargo anterogradely toward microtubule plus ends (cell periphery). Dynein moves cargo retrogradely (toward minus ends).
Related Question 5
During the G1/S transition in the eukaryotic cell cycle, phosphorylation of the retinoblastoma (Rb) protein results in which of the following?
  • A. Release of E2F transcription factors, activating S-phase gene expression
  • B. Activation of cyclin-dependent kinase inhibitors to halt cell cycle progression
  • C. Induction of apoptosis via activation of p53
  • D. Inhibition of cyclin D synthesis
Correct Answer: A
Explanation:
Phosphorylated Rb releases bound E2F transcription factors, which then activate genes required for DNA replication in S phase.