Question 33

[yikang_xu4881]

I have problem including cholesterol among steroids. It is the precursor for steroid synthesis, but definitely not a steroids by definition.

none of the choices offered seems correct.

[admin]

By definition, cholesterol is a sterol which is a subgroup of steroids. I think that your discomfort was caused by the common expression "cholesterol is a precursor of steroid hormones." Note that it is a precursor to this important category of hormones (another subcategory of steroids), but it is indeed a steroid itself.

Ref:

http://www.answers.com/topic/sterol?cat=health

[yikang_xu4881]

are sterols and steroids the same entity?

i thought steroids have their side chain cleaved(the irreversible step in steroid synthesis), while sterols have intact side chain.

hopefully mcat will test this topic.

--still confused.

[admin]

Sterols are a subgroup of steroids. In fact, the word "steroids" was coined by Callow (Proc Royal Soc London series A 1936, 157, 194; don't memorize!) to refer to "the group of compounds comprising the sterols, bile acids, heart poisons, saponins, and sex hormones".

Synthesis of steroids, unless relevant information is provided in the passage, is beyond required knowledge for the new MCAT.

[jvuofm1709]

this is regarding question #34, which does not have a discussion forum. In GLC, the stationary phase is a liquid which coats the tubes, not a solid stationary phase. This immediately eliminates choice A as correct. A liquid is used since it acts to dissolve the lipid molecules (different polarities are used to achieve differentiable dissolving abilities), and the lipid vapor is passed through in an inert gas mobile phase. Whereas in column chromatography, an elutant is used to elute the different phase, in GLC an oven is used to heat the tubes, thereby vaporizing the dissolved gas molecules from the stationary phase (that is, even if they dissolved). The two primary factors effecting GLC separation are thus A) the solubility of the lipid in the stationary phase and B) the BOILIING POINT of the lipids.

[jvuofm1709]

I just read on wikipedia that GLC can also use a solid polymer as its stationary phase (I also confirmed this in my biochem book: Lehninger Principles of Biochemistry 5th edition) However, option A says that the lipids are ABSORBED by the solid stationary phase of the GLC column...they are ADSORBED, so it is still incorrect.

[mohsinalam5969]

A steroid is a type of organic compound that contains a specific arrangement of four cycloalkane rings that are joined to each other. Examples of steroids include the dietary fat cholesterol, the sex hormones estradiol and testosterone, and the anti-inflammatory drug dexamethasone.
Cortisone is a steroid hormone. In chemical structure, it is a corticosteroid closely related to corticosterone. It is used to treat a variety of ailments and can be administered intravenously, orally, intraarticularly, or cutaneously. Cortisone suppresses the immune system, thus reducing inflammation and attendant pain and swelling at the site of the injury.
Cortisone is one of several end-products of a process called steroidogenesis. This process starts with the synthesis of cholesterol, which then proceeds through a series of modifications in the adrenal gland (suprarenal) to become any one of many steroid hormones. One end-product of this pathway is cortisol.

i hope that this knowledge is enough to explain that all these are steroids.