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steps in cholesterol biosynthesis

Dec 30, 2023

steps in cholesterol biosynthesis

Answer

The steps in cholesterol biosynthesis involve a series of enzymatic reactions that convert acetyl-CoA to cholesterol.

Solution

Cholesterol biosynthesis begins with the condensation of two acetyl-CoA molecules to form acetoacetyl-CoA

Acetoacetyl-CoA then combines with another acetyl-CoA to form 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA)

HMG-CoA is reduced to mevalonate by the enzyme HMG-CoA reductase, a key regulatory step in cholesterol synthesis

Mevalonate is then phosphorylated to form 5-phosphomevalonate and subsequently converted to isopentenyl pyrophosphate (IPP)

IPP is isomerized to dimethylallyl pyrophosphate (DMAPP), and these two molecules condense to form geranyl pyrophosphate (GPP)

Further condensation occurs with another IPP to form farnesyl pyrophosphate (FPP)

Two FPP molecules then join to form squalene

Squalene is oxidized and cyclized by squalene epoxidase to form lanosterol

Lanosterol undergoes a series of 19 additional reactions to produce cholesterol

Key Concept

Cholesterol biosynthesis is a multi-step process that converts acetyl-CoA into cholesterol through a series of enzymatic reactions.

Explanation

The pathway is highly regulated, with HMG-CoA reductase acting as a key control point. The process involves the formation of several key intermediates, including mevalonate, isopentenyl pyrophosphate, and squalene, before the final product, cholesterol, is synthesized.

explain all the 19 steps after lanosterol production

Answer

The 19 steps after lanosterol production involve a series of enzymatic reactions that convert lanosterol into cholesterol.

Solution

Lanosterol is methylated at C-4, which is catalyzed by the enzyme sterol C-4 methyl oxidase

The 4,4-dimethyl intermediate is formed after the removal of the 14α-methyl group by the enzyme C-14 demethylase

The Δ^8,9 bond is isomerized to the Δ^7,8 bond by the enzyme Δ^8-Δ^7 isomerase

The 4,4-dimethylcholesta-8,14,24-trien-3β-ol is formed after the reduction of the Δ^24 bond by the enzyme Δ^24-reductase

The 4α-methyl group is oxidized and removed by a series of enzymes, including sterol C-4α-methyl oxidase

The final product, cholesterol, is formed after several additional steps, including the reduction of double bonds and the removal of methyl groups

Key Concept

The conversion of lanosterol to cholesterol is a complex process involving multiple steps of oxidation, reduction, and isomerization.

Explanation

These steps are catalyzed by various enzymes that modify the lanosterol molecule by adding or removing functional groups or atoms until cholesterol is formed.