Question

Considering the final steps in cholesterol biosynthesis, when squalene is eventually converted to lanosterol, which of the following statements is wrong?a. The action of squalene monooxygenase oxidizes C14 of the squalene chain, forming an epoxideb. Squalene is joined at carbons 1 and 30 to form the fused ring structure of sterolsc. All of the sterols have three fused rings (the steroid nucleus) and are alcohols with a hydroxyl group at carbon C3d. I Squalene monooxygenase uses reduced flavin nucleotides, such as FAD (2H), as the cosubstrate in the reactione. Squalene monooxygenase is considered a mixed function oxidase because it catalyzes a reaction in which only one of the oxygen atoms of O2 is incorporated into the organic substrate

Answer 1

All of the sterols, including cholesterol, have four fused rings, not three as one of the choices incorrectly suggests. Squalene monooxygenase, which uses FAD (2H), is indeed significant in cholesterol biosynthesis.

Step-by-step explanation:

The question pertains to the final steps in cholesterol biosynthesis, focusing on the conversion of squalene into lanosterol and eventually towards the formation of cholesterol. Among the choices provided, the incorrect statement is that all of the sterols have three fused rings (the steroid nucleus) and are alcohols with a hydroxyl group at carbon C3. Sterols, including cholesterol, actually possess a structure with four fused rings, typically three six-membered rings and one five-membered ring.

Squalene monooxygenase is indeed involved in one of the later stages of cholesterol biosynthesis. It uses FAD (2H), or flavin adenine dinucleotide in its reduced form, as a cosubstrate in the reaction to oxidize the C14 of the squalene.

The enzyme can be considered a mixed function oxidase due to its reaction mechanism where only one of the oxygen atoms from molecular oxygen (O₂) is incorporated into the organic substrate.

Answer 2

Among all the options 4 options are wrong.

Wrong options:

a. The action of squalene monooxygenase oxidizes C14 of the squalene chain, forming an epoxide

b. Squalene is joined at carbons 1 and 30 to form the fused ring structure of sterols

c. All of the sterols have three fused rings (the steroid nucleus) and are alcohols with a hydroxyl group at carbon C3

d. I Squalene monooxygenase uses reduced flavin nucleotides, such as FAD (2H), as the cosubstrate in the reaction

Correct Option:

e. Squalene monooxygenase is considered a mixed function oxidase because it catalyzes a reaction in which only one of the oxygen atoms of O2 is incorporated into the organic substrate

Reference Book:

Marks' Basic Medical Biochemistry

Chapter 34

Cholesterol Absorption, Synthesis, Metabolism, and Fate