Before You Begin
Question #45212
The Question
In a patient with Severe Combined Immunodeficiency (SCID) caused by Adenosine Deaminase (ADA) deficiency, lymphocytes fail to proliferate upon antigenic stimulation due to the arrest of DNA replication. Which of the following best explains the inability of DNA polymerase to catalyze nucleotide phosphate esterification (phosphodiester bond formation) in these cells?
Options
- A.
Accumulation of dATP inhibits ribonucleotide reductase, depleting the pool of other dNTPs required as substrates for esterification.
- B.
Excess deoxyadenosine competitively inhibits DNA polymerase, directly blocking the formation of phosphodiester bonds at the replication fork.
- C.
The absence of ADA prevents the synthesis of RNA primers, as DNA primase requires inosine to initiate nucleotide polymerization.
- D.
Toxic accumulation of adenosine directly degrades the sugar-phosphate backbone, reversing the esterification process in mature lymphocytes.
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Regulatory_Failure
Understand how NOT, EXCEPT, and logical constraints are used to manipulate exam results.
Concepts Behind This Question
DNA_Polymerase|Adenosine_Deaminase|dATP_accumulation
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize that ADA deficiency causes SCID (NCERT Biotechnology) but fail to connect the biochemical consequence to the exact molecular failure in DNA replication (Molecular Basis of Inheritance).
The trap relies on confusing direct inhibition of DNA polymerase (Option B) with the actual indirect mechanism of substrate starvation via ribonucleotide reductase inhibition (Option A).
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Biomolecules - Class 11 |
| Concept | Nucleotide Phosphate Esterification |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |