Biology Biotechnology PMDC Conceptual Practice
PMDC Verified Question 14 of 65
Sanger's DNA sequencing method relies on dideoxynucleotides (ddNTPs), which lack an -OH group at carbon:
A
\( 1' \)
B
\( 2' \)
C
\( 3' \)
D
\( 5' \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: \( 3' \)
Concept:

Chain-termination mechanism of dideoxynucleotides in automated DNA sequencing.

Solution:

Dideoxynucleotides (ddNTPs) lack a hydroxyl group (\( \text{-OH} \)) at the \( 3' \) position of the deoxyribose sugar. Once incorporated into a growing DNA chain, no further phosphodiester bond can be formed, causing immediate chain termination.

Why other options are incorrect:

  • \( 1' \) carbon: The nitrogenous base is attached to the \( 1' \) carbon via an N-glycosidic bond.


  • \( 2' \) carbon: Standard deoxynucleotides (dNTPs) already lack an \( \text{-OH} \) at carbon \( 2' \) (having \( \text{-H} \) instead).


  • \( 5' \) carbon: The phosphate group is attached to the \( 5' \) carbon, which is necessary for entry into the active site.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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