The Question is from neet-zoology , and it was created by the author T SAILAJA

Question

A person with a mutation in the gene encoding rhodopsin kinase experiences prolonged photobleaching after exposure to bright light. This is MOST likely due to:

T SAILAJA · Accepted Answer

## CORE INFORMATION
✓ **Answer**: D
## CONCEPT FRAMEWORK
 **Primary Concept**: Phototransduction in the retina
 **Related Topics**: Rhodopsin, Metarhodopsin II, Rhodopsin kinase, Photobleaching
 **Prerequisites**: Understanding of the visual transduction cascade.
## SOLUTION PATHWAY
**Given Information**:
  A mutation in the gene encoding rhodopsin kinase leads to prolonged photobleaching.
  Photobleaching is prolonged after exposure to bright light.
**Method & Steps**:
 1. Understand the role of rhodopsin kinase in phototransduction.
  Reasoning: Rhodopsin kinase is crucial for inactivating metarhodopsin II, a key step in the recovery from light stimulation.  Without proper inactivation, the photoreceptor cell remains in a stimulated state.
  Formula/Rule: No specific formula is applicable here; it's a qualitative understanding of the biochemical pathway.
 2. Analyze the effect of a rhodopsin kinase mutation.
  Working: A mutation in the rhodopsin kinase gene would likely result in a non-functional or less-functional enzyme. This means metarhodopsin II would not be deactivated efficiently.
  Key Point:  Metarhodopsin II is an activated form of rhodopsin; its prolonged presence leads to prolonged signaling and photobleaching.
 3. Relate the prolonged photobleaching to the mutation.
  Result: The prolonged photobleaching is directly caused by the delayed inactivation of metarhodopsin II due to the dysfunctional rhodopsin kinase.
  Verification: This aligns with the known role of rhodopsin kinase in the visual transduction pathway.
 ## OPTION ANALYSIS
A :x: Increased sensitivity of transducin to light: This is not directly related to the rhodopsin kinase's role in metarhodopsin II inactivation.
B :x: Delayed regeneration of rhodopsin: While rhodopsin regeneration is part of the recovery process, the primary effect of the mutation is on metarhodopsin II inactivation, which happens before rhodopsin regeneration.
C :x: Increased synthesis of cGMP: cGMP levels are regulated downstream of rhodopsin activation. The primary problem is the failure to properly inactivate the activated rhodopsin.
D ✓: Delayed inactivation of metarhodopsin II: This directly explains the prolonged photobleaching because metarhodopsin II remains active, leading to sustained signaling. 
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing the roles of different proteins in the phototransduction cascade:  Carefully study the steps and the roles of rhodopsin, transducin, phosphodiesterase, and rhodopsin kinase.
  2.Assuming that the mutation affects rhodopsin directly: The mutation affects the enzyme that inactivates metarhodopsin II, not rhodopsin itself.
 **Quick Tips**:
  1.Visualize the phototransduction cascade as a series of activation and inactivation steps.
  2.Remember that rhodopsin kinase is the key player in turning off the signal.

T SAILAJA · Answer

Increased sensitivity of transducin to light

T SAILAJA · Answer

Delayed regeneration of rhodopsin

T SAILAJA · Answer

Increased synthesis of cGMP

T SAILAJA · Answer

The correct Option is "Delayed inactivation of metarhodopsin II"

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