Selected MCQ

Current Question
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 1
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 2
Which organelle is primarily responsible for lipid synthesis and detoxification of drugs in liver cells?
  • A. Rough endoplasmic reticulum
  • B. Smooth endoplasmic reticulum
  • C. Golgi apparatus
  • D. Mitochondrion
Correct Answer: B
Explanation:
Smooth ER contains enzymes involved in lipid metabolism and drug detoxification (e.g., cytochrome P450s), especially in hepatocytes.
Related Question 3
Which feature of mitochondrial structure most directly facilitates ATP synthesis via oxidative phosphorylation?
  • A. Large pores in the outer membrane allowing free movement of ions
  • B. Extensive folding of the inner membrane into cristae
  • C. Circular DNA encoding the majority of electron transport proteins
  • D. Abundant ribosomes within the mitochondrial matrix
Correct Answer: B
Explanation:
The inner mitochondrial membrane is highly folded into cristae, increasing surface area for the electron transport chain complexes and ATP synthase to produce ATP.