The Question is from neet-botany molecular-basis-of-inheritance , and it was created by the author K SURESH KUMAR

Question

If a mutation prevented the lac repressor from binding to allolactose, what would be the likely outcome for the lac operon?

K SURESH KUMAR · Accepted Answer

## CORE INFORMATION
✓ **Answer**: A
## CONCEPT FRAMEWORK
 **Primary Concept**:  The impact of mutations on the lac operon's regulation.
 **Related Topics**:  Lac repressor, allolactose, gene regulation, mutations.
 **Prerequisites**:  Understanding of the lac operon's normal function.
## SOLUTION PATHWAY
**Given Information**:
  The question describes a mutation preventing the lac repressor from binding to allolactose.
**Method & Steps**:
 1. Recall the role of allolactose in repressor binding.
  Reasoning: Allolactose is the inducer; it binds to the repressor, causing a conformational change that prevents it from binding to the operator.
  Formula/Rule: None directly applicable; this is a conceptual understanding.
 2. Determine the effect of the mutation.
  Working: If the repressor can't bind allolactose, it will remain bound to the operator regardless of lactose's presence.  This means the lac operon will always be repressed.
  Key Point: The inability of the repressor to bind the inducer essentially renders the operon constitutively repressed.
 3. Select the correct answer.
  Result: The operon would be constitutively repressed.
  Verification:  The other options describe outcomes that are inconsistent with the given mutation.
 ## OPTION ANALYSIS
A] ✓: The mutation prevents allolactose from inactivating the repressor, leading to continuous repression of the lac operon.
B] :x: Constitutive expression would occur if the repressor couldn't bind to the operator at all.
C] :x: Normal function requires the repressor to bind allolactose and release from the operator in the presence of lactose.
D] :x: The repressor would still bind to the operator in the absence of allolactose, but the question specifies a binding failure with allolactose.
 ## LEARNING AIDS
 **Common Mistakes**: Confusing constitutive repression with constitutive expression.
  1. [Error 1]: Predicting constitutive expression. [How to avoid]:  Consider that the repressor remains active, blocking transcription continuously.
  2. [Error 2]: Misunderstanding the role of allolactose. [How to avoid]:  Focus on allolactose's role in inactivating the repressor.
 **Quick Tips**:  Consider the consequence of a permanently active repressor.

K SURESH KUMAR · Answer

The correct Option is "The operon would be constitutively repressed."

K SURESH KUMAR · Answer

The operon would be constitutively expressed.

K SURESH KUMAR · Answer

The operon would function normally.

K SURESH KUMAR · Answer

The repressor would bind to the promoter.

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