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Question #45762
The Question
To survive in a hyperosmotic marine environment, cartilaginous fishes retain urea as an osmolyte. If a sudden increase in environmental salinity demands rapid transcriptional upregulation of the urea cycle enzyme Carbamoyl Phosphate Synthetase I (CPS-I), which of the following molecular events at the chromatin level must occur to prevent cellular crenation?
Options
- A.
Histone acetyltransferases neutralize the positive charges on lysine and arginine side chains, decreasing DNA-histone affinity.
- B.
Histone deacetylases restore the positive charges on the histone octamer, promoting the formation of transcriptionally active euchromatin.
- C.
The negatively charged phosphate backbone of the CPS-I gene is heavily methylated to repel the positively charged histone core.
- D.
The H1 histone tightly binds the linker DNA to facilitate the immediate binding of RNA polymerase to the promoter region.
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
Urea_Cycle|Gene_Expression|Hyperosmotic_Stress
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: This question tests the synthesis of Chapter 19 (Excretory Products - Osmoregulation via urea) and Chapter 6 (Molecular Basis of Inheritance - Packaging of DNA helix).
The common misconception is failing to link the biochemical mechanism of epigenetic modification (acetylation neutralizing the positive charge of basic amino acids) to a macro-physiological adaptation.
Students often memorize 'acetylation = activation' without understanding the underlying electrostatic charge dynamics explicitly detailed in NCERT.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Excretory Products and Their Elimination - Class 11 |
| Concept | Osmoregulation in Aquatic Adaptations |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |