Selected MCQ

Current Question
A newly synthesized protein is destined for secretion outside the cell. Which sequence or signal will it most likely contain?
  • A. A hydrophobic transmembrane domain
  • B. A nuclear localization signal
  • C. A signal peptide at the N-terminus
  • D. A peroxisomal targeting signal at the C-terminus
Correct Answer: C
Explanation:
Secreted proteins typically have an N-terminal signal peptide that directs the ribosome to the ER for co-translational translocation into the secretory pathway.
Related Question 1
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).
Related Question 2
Gap junction channels between animal cells are formed by which protein?
  • A. Connexin
  • B. Cadherin
  • C. Integrin
  • D. Actin
Correct Answer: A
Explanation:
Connexins assemble into connexons that align between adjacent cells to form gap junction channels for direct cytoplasmic communication.
Related Question 3
An ER-resident protein contains a C-terminal KDEL sequence. If this sequence is missing, what would likely happen to the protein?
  • A. It would be transported to the Golgi
  • B. It would be secreted from the cell
  • C. It would remain in the cytosol
  • D. It would be targeted to mitochondria
Correct Answer: B
Explanation:
KDEL is an ER retention signal. Without KDEL, the protein is not retrieved from the Golgi and is secreted.
Related Question 4
Overexpression of the Bcl-2 protein in a cell would most likely result in which effect?
  • A. Increased apoptosis
  • B. Enhanced autophagy
  • C. Resistance to apoptosis
  • D. Increased necrosis
Correct Answer: C
Explanation:
Bcl-2 is an anti-apoptotic protein. Its overexpression makes cells more resistant to apoptotic signals, promoting cell survival.
Related Question 5
Activation of a Gs protein-coupled receptor typically leads to stimulation of which enzyme to increase intracellular cAMP?
  • A. Protein kinase C
  • B. Adenylyl cyclase
  • C. Phosphodiesterase
  • D. Guanylyl cyclase
Correct Answer: B
Explanation:
Gs α-subunit activates adenylyl cyclase, which converts ATP to cAMP, raising second-messenger levels.