Cholesterol is utilized as a precursor for sterioid hormone biosynthesis which t

Question

Cholesterol is utilized as a precursor for sterioid hormone biosynthesis which takes place within the endoplasmic reticulum of the cell. Which process would be necessary part of getting chloesterol coming from food into the cell and then into the endoplasmic reticulum.

A) Cholesterol utilizing an energy dependent transporter to cross a membrane
B) Cholesterol freely diffusing across the lipid bilayer
C) Cholesterol changing the fludity of membranes in order to pass through them.
D) Cholesterol being insoluble in the cytoplasm
E) Cholesterol being acted on through post-translational modification

I think it is B, but can you explain why the correct answer is the most important?

Explanation / Answer

Cholesteol is a precursor for steroidal harmone synthesis by the enzymes which are located in mitochondria and smooth endoplasmic reticulum where cholesterol content is low.

So cholesterol is transported from outer cellular membrane to inner cellular membrane. As cholesterol is a lipid soluble and free cholesterol located at external mitochondrial membrane.

This transport of cholesterol is a rate limiting step in steroidal biosynthesis because as cholesterol is hydrophobic it cannot diffuse directly into aqueous environment in the mitochondria.

So cholesterol is insoluble in cytoplasm and appear either as free form or in the form of ester.

They are transported through signal transduction and membrane traffic.

StAR protein (steroidogenic acute regulatory protein) and translocator proteins helps in the transport of cholesterol which is converted to pregnenolone by P450 scc (side chain cleavage enzyme) which initiates the steroidal harmone synthesis.

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