The Question is from neet-botany photosynthesis-in-higher-plants dark-phase, and it was created by the author B VENKAT

Question

A mutation in a plant affects the enzyme responsible for converting glyceraldehyde-3-phosphate (G3P) to dihydroxyacetone phosphate (DHAP). Which of the following is the MOST likely direct consequence of this mutation on the Calvin cycle?

B VENKAT · Accepted Answer

## CORE INFORMATION
✓ **Answer**: D
## CONCEPT FRAMEWORK
 **Primary Concept**: Calvin Cycle and Enzyme Function
 **Related Topics**: Photosynthesis, Carbohydrate Metabolism, Enzyme Kinetics
 **Prerequisites**: Understanding of the Calvin cycle, the role of G3P and DHAP, and the interconversion between them.
## SOLUTION PATHWAY
**Given Information**:
  A mutation affects the enzyme responsible for converting G3P to DHAP.
  The enzyme in question is involved in the Calvin cycle.
**Method & Steps**:
 1. Identify the role of the G3P to DHAP interconversion in the Calvin cycle.
  Reasoning:  The Calvin cycle involves a series of reactions to convert $CO_2$ into carbohydrates. G3P and DHAP are triose phosphates that are isomers.  The interconversion between them is crucial for the efficient functioning of the cycle and the subsequent export of carbohydrates.
  Formula/Rule:  The interconversion is catalyzed by triose phosphate isomerase.
 2. Analyze the consequence of the mutation.
  Working: If the enzyme converting G3P to DHAP is affected, the equilibrium between these two molecules will be disrupted. This will directly affect the availability of DHAP for the synthesis of other sugars.  G3P will accumulate, and the export of triose phosphates from the chloroplast, which are precursors for sucrose synthesis, will decrease.
  Key Point: The interconversion of G3P and DHAP is essential for the smooth operation of the Calvin cycle and the subsequent production of carbohydrates.
 3. Determine the most likely direct consequence.
  Result: The most direct consequence is a reduced export of triose phosphates from the chloroplast and impaired sucrose synthesis.
  Verification: This option aligns with the disruption of the G3P-DHAP equilibrium and its impact on carbohydrate synthesis and export.
 ## OPTION ANALYSIS
A :x: Complete cessation of the Calvin cycle is unlikely. While the mutation affects a key step, other parts of the cycle might still function, albeit less efficiently.
B :x: Accumulation of 3-PGA (3-phosphoglycerate) is an indirect consequence.  The mutation's direct effect is on the conversion of G3P to DHAP.
 C :x: Increased RuBisCO activity is not a direct consequence. RuBisCO activity is regulated by various factors, and this mutation primarily affects the downstream process.
D ✓: Reduced export of triose phosphates from the chloroplast and impaired sucrose synthesis is the most likely direct consequence of the mutation, as it directly affects the pool of triose phosphates available for export and subsequent sucrose synthesis.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing the direct and indirect effects of the mutation: Focus on the immediate impact of the enzyme deficiency.
  2.Oversimplifying the Calvin cycle: Understanding the interconnectedness of its steps is crucial for accurate analysis.
 **Quick Tips**:
  1.Visualize the Calvin cycle and the role of G3P and DHAP in the pathway.
  2.Remember that enzymes are catalysts that maintain equilibrium; disrupting an enzyme disrupts the equilibrium.

B VENKAT · Answer

Complete cessation of the Calvin cycle

B VENKAT · Answer

Accumulation of 3-PGA

B VENKAT · Answer

Increased RuBisCO activity

B VENKAT · Answer

The correct Option is "Reduced export of triose phosphates from the chloroplast and impaired sucrose synthesis"

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