Hormone Structures?

[banana_phone]

Hi everyone -

I'm going over the reproduction and endocrinology chapters in BR right now. Some of the practice passages require you to know the structures of the different hormones - cortisol, testosterone, etc..

Is this something I should memorize for the exam, a la the amino acids? Or is this Berkeley Review being tough and not representative of material I will need to have memorized for the MCAT? Obviously knowing hormone classes is important, but not sure about specific structures.

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[Dr. Trenb]

Though I don't believe you are required to memorize their structures, be familiar with them. Specifically, learn to differentiate between these main steroid classes; Cholesterol, Progestogen, Androgen and Estrogen.

It is not that difficult to recognize which is which if you remember these two points:

1. The General Steroid Structure (4 rings)
http://www.nbs.csudh.edu/chemistry/faculty/nsturm/CHE452/images/SteroidStruc.gif

2. The descending order of their synthesis, which is reflected by their size (# of Carbons)
http://alaskadigitalvisions.com/femalehormones/ImagesGeneral/003Steroidogenesis288.jpg
Cholesterol comes first (27 Carbons) ➙ progesterone (21 Carbons) ➙ androgen (testosterone, 19 Carbons) ➙ estrogen (18 Carbons)
You don't have to remember the exact number of carbons, just remember their order in terms of their size

Basically, whenever you come over a question regarding these hormones, look for:
- The carbon skeleton with four fused rings (to rule out everything but steroids)
-See if there is a carbon connected to carbon 10 (between ring A and B, carbon #19): If no carbon there, then it's not cholesterol, androgen, glucocorticoid, or mineralocorticoid. It has to be an estrogen (again, estrogen is the smallest of the bunch)
- If a carbon is connected to carbon 10 (between ring A & B), look for carbons 20&21 on ring D. If you find these 2 carbons there, it can't be an androgen or estrogen (Note: I am only focusing on Carbon connection to the ring, Not Oxygen or other elements)

This method doesn't help if you are looking at a specific class and its sub-types. For example, if you are trying to figure out an estradiol from estrone. But that's outside the scope of the MCAT.

 

[rsrs3739]

You don't need to memorize the structures of specific hormones but you do need to be able to distinguish between cholesterol and peptide hormones, which tells you the hormone is either hydrophilic or hydrophobic.
Do memorize the structures and side chain properties of ALL 20 amino acids and both 3 and 1 letter codes.



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[ag9124]

I would say memorizing hormone structures is low yield, i can't recall of any question asking specifically of a steroid structure on the real mcat. I would mainly focus on learning general trends as others have mentioned. It's a different story when it comes to amino acids however. Learn those inside out.