Mystery Molecule

[TomCat]

Hello.

This is my first post on here so please forgive me if I do something wrong. I've read the rules and I've researched this question thoroughly, collaborated with others, and used reasoning, but I'm not 100% confident in my answer and I'd appreciate some clarification.

The question is as follows:

What is the structure shown in the figure below?



a) starch molecule
b) protein molecule
c) steroid molecule
d) cellulose molecule
e) phospholipid molecule

My Answer: C. steroid molecule. However, a lot of students in my class are disagreeing with my answer, and I am starting to understand why. I looked up structural formulas of steroids, and the closest structure I found to the one pictured above was that of cholesterol. However, there is a pentagonal carbon structure in cholesterol that appears as a hexagonal carbon structure in the structural formula in the question above. Therefore, I know it's not cholesterol. However, is the image I've posted above still a steroid? I don't think it can be a protein because it doesn't have an amine group or a carboxylic acid group. It can't be a starch because it doesn't contain carbon 1-4 glycosidic linkages, and it can't be cellulose for pretty much the same reason (beta carbon 1-4 glycosidic linkages). A phosopholipid molecule has a phosphate-containing portion with a glycerol and two fatty acids "hanging" off of it, so it can't be that. So, if I'm correct, the only logical answer would be C, a steroid molecule. Now, I'm only an AP Biology student so I'm by no means any kind of expert, but this just seems to make sense.

Can anyone confirm my answer please? And, if I'm wrong, could you please give me an explanation of why I am wrong so I know not to make this mistake in the future?

Thank you in advance for your helpful responses.

[canalon]

Yep it does not seem to have the sterol structure (that includes the pentagonal ring) and that defines steroids (see plenty here: http://en.wikipedia.org/wiki/File:Steroidogenesis.svg). But your reasons to eliminates all the others are perfectly correct. So I feel a bit confused like you. It might be a problem with your prof drawing the molecule though...

[JackBean]

notice, that it has whole extra cycle from the cholesterol However, I still think that's a steroid, I think there exists something like that, but I wasn't succesfull searching it...

[JackBean]

try to go to http://pubchem.ncbi.nlm.nih.gov/search/search.cgi#
and go to Substructure/Suprestructure / CID, SMILES/SMARTS, InChI and enter OC2CCC3C4CCC1C5CCCCC5CCC1C4CC=C3C2
so you will get some idea, what it could be...

[ccarlee]

I answered the question with "steroid molecule" and got it correct.

[JackBean]

obviously nothing else could be correct