Selected MCQ

Current Question
On which end of a tRNA molecule is the amino acid attached during translation?
  • A. 5′ end
  • B. 3′ end
  • C. D-loop
  • D. Anticodon loop
Correct Answer: B
Explanation:
The 3′-terminal CCA sequence of tRNA is where aminoacyl-tRNA synthetases covalently attach the amino acid.
Related Question 1
A point mutation changes a codon for an amino acid to a stop codon. This is called a:
  • A. Missense mutation
  • B. Silent mutation
  • C. Nonsense mutation
  • D. Frameshift mutation
Correct Answer: C
Explanation:
Changing an amino acid codon to a stop codon prematurely terminates translation, producing a truncated protein; this is a nonsense mutation.
Related Question 2
During the eukaryotic cell cycle, which checkpoint ensures that all chromosomes are correctly attached to the mitotic spindle before proceeding to anaphase?
  • A. G1/S checkpoint
  • B. G2/M checkpoint
  • C. Spindle (metaphase) checkpoint
  • D. S-phase checkpoint
Correct Answer: C
Explanation:
The spindle assembly (metaphase) checkpoint monitors attachment of all kinetochores to spindle microtubules. It prevents the onset of anaphase until all chromosomes are properly aligned and attached.
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
In a DNA molecule, 5′ to 3′ synthesis means:
  • A. New nucleotides are added at the 5′ end of the new strand
  • B. New nucleotides are added at the 3′ end of the new strand
  • C. DNA is always read 5′ to 3′ on the template
  • D. The sugar backbone runs from 5′ to 3′
Correct Answer: B
Explanation:
DNA polymerases add nucleotides to the 3′-OH end of a growing strand, so synthesis proceeds in the 5′→3′ direction (extending at the 3′ end).
Related Question 5
Which of the following is NOT typically controlled during industrial fermentation in a bioreactor?
  • A. Temperature
  • B. pH
  • C. Oxygen concentration
  • D. DNA sequence of the microorganism
Correct Answer: D
Explanation:
A, B, and C (temperature, pH, oxygen) are critical parameters controlled in fermentation. The chosen strain fixes the DNA sequence and is not a controlled parameter during the run.