Before You Begin
Question #47705
The Question
During a recombinant DNA experiment, a researcher uses a restriction endonuclease that generates blunt ends to cut both the plasmid vector and the foreign DNA. Despite adding an optimal concentration of DNA ligase and ATP, the yield of recombinant plasmids is drastically lower than a parallel experiment using EcoRI. Which of the following best explains this kinetic bottleneck?
Options
- A.
DNA ligase is strictly specific to single-stranded DNA overhangs and cannot bind to double-stranded blunt ends.
- B.
The absence of complementary cohesive ends prevents transient hydrogen bonding, reducing the probability of the fragments aligning for phosphodiester bond formation.
- C.
Blunt-end cleavage removes the terminal 5'-phosphate groups, leaving only 3'-hydroxyl groups that cannot undergo condensation.
- D.
The blunt ends spontaneously undergo complementary base pairing with themselves, preventing the insertion of the foreign DNA.
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
Restriction Endonuclease | Viral Vector | Gene Therapy
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize the NCERT line 'sticky ends facilitate the action of the enzyme DNA ligase' without understanding the underlying thermodynamic mechanism.
The trap is assuming that blunt ends lack the necessary chemical functional groups (Option C) or that ligase is entirely incapable of joining them (Option A).
The true bottleneck is kinetic: the lack of transient hydrogen bonding reduces the probability of the substrates aligning correctly in the enzyme's active site.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Biotechnology : Principles and Processes - Class 12 |
| Concept | Restriction Endonuclease Nomenclature |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |