The Question is from neet-botany biomolecules-biology lipid, and it was created by the author D VINOD

Question

Which statement regarding the biosynthesis of cholesterol is INCORRECT?

D VINOD · Accepted Answer

## CORE INFORMATION
✓ **Answer**: D
## CONCEPT FRAMEWORK
	**Primary Concept**: Cholesterol Biosynthesis
	**Related Topics**: Mevalonate Pathway, Isoprenoid Pathway, HMG-CoA Reductase, Squalene, Steroidogenesis
	**Prerequisites**: Basic biochemistry, enzyme regulation, metabolic pathways
## SOLUTION PATHWAY
**Given Information**:
	The question asks for the INCORRECT statement about cholesterol biosynthesis.
**Method & Steps**:
	1. Analyze each statement about cholesterol biosynthesis.
	2. Identify the statement that is factually incorrect based on established biochemical principles.
	3. Select the incorrect statement as the answer.
## OPTION ANALYSIS
[A] ✓: HMG-CoA reductase is the rate-limiting enzyme in cholesterol biosynthesis. This statement is correct. HMG-CoA reductase catalyzes the conversion of HMG-CoA to mevalonate, a crucial and regulated step in the cholesterol biosynthesis pathway.
[B] ✓: The process occurs primarily in the liver. This statement is correct. While cholesterol synthesis can occur in other tissues, the liver is the primary site of cholesterol biosynthesis.
[C] ✓: NADPH provides the reducing equivalents for the biosynthesis of cholesterol. This statement is correct.  NADPH is the primary source of reducing power for the numerous reductive steps involved in cholesterol synthesis.
[D] :x: Oxygen is directly involved in the condensation of isoprene units to form squalene. This statement is incorrect. While oxygen is required for cholesterol biosynthesis as a whole, it is *not* directly involved in the formation of squalene from isoprene units. This step involves a reductive 'head-to-head' condensation of two farnesyl pyrophosphate molecules, and NADPH provides the reducing equivalents. Molecular oxygen is not directly involved in this specific reaction.  Oxygen *is* required later in the pathway for the conversion of squalene to lanosterol, which is then further modified to form cholesterol.
## LEARNING AIDS
	**Common Mistakes**:
		1. Confusing the roles of NADPH and oxygen in cholesterol synthesis: Remember that NADPH is the reducing agent, while oxygen is involved in later oxidation steps.
		2. Assuming that all steps in a long biosynthetic pathway require oxygen: Many biosynthetic reactions are reductive and do not directly involve oxygen.
	**Quick Tips**:
		1. Remember the key regulatory enzyme: HMG-CoA reductase.
		2. Recall the primary site of synthesis: The liver.

D VINOD · Answer

HMG-CoA reductase is the rate-limiting enzyme in cholesterol biosynthesis.

D VINOD · Answer

The process occurs primarily in the liver.

D VINOD · Answer

NADPH provides the reducing equivalents for the biosynthesis of cholesterol.

D VINOD · Answer

The correct Option is "Oxygen is directly involved in the condensation of isoprene units to form squalene."

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