Discussion of all aspects of biological molecules, biochemical processes and laboratory procedures in the field.
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Ok, this may be a very stupid and simple question, but nevertheless I still need an answer. Why is it that the chemical formula of Glucose (C6H12O6) has 6 Carbon atoms, 12 Hydrogen and 6 Oxygen atoms, but when I actually look at the macromolecule in a 3d structure I can only see ONE Carbon atom, 12 Hydrogen atoms and 6 Oxygen atoms?
Like I said before this is probably a very simple question, but I have stagnated at this point, as I cannot continue my work until I grasp this idea and figure out this problem.
Any help would be greatly appreciated and very well recieved.
P.S. I am doing a Gr.12 course so please keep this answer simple.
Last edited by Gumber on Wed Mar 12, 2008 6:06 pm, edited 1 time in total.
Your problem comes from not being familiar with the different ways to represent chemical structures. You’ve got a distorted Haworth projection of the cyclic or pyranose form of glucose. There are carbon atoms at each vertex of the hexagon (except the one occupied by an oxygen atom). If you count the vertices as one carbon each and add to that count the explicit carbon atom, you should get 6. Try the open, linear formula:
Each cross represents a carbon. See fig with C filled in:
Not really to answer the question, which has already been done, I think, but as "macromolecules" go, glucose isn't very macro. It only has a molecular weight of 180. From the title you gave the thread, I thought it was going to be a question about proteins, which typically have thousands of atoms of carbon, oxygen and nitrogen, not to mention a few sulfurs and miscellaneous metals and phosphorus. Your question really was about how to interpret a molecular formula. That's fine. I'm not meaning to criticize you. Now you know.
For crystallographers the distinction between small molecule and macromolecule tends to be set at the current limit of direct methods to easily solve a structure. Right now that limit is somewhere in the vicinity of 700 non-hydrogen atoms, which would be a MW in the vicinity of 7-10,000. It is possible to routinely solve 300 atom-or-fewer structures with nothing but intensity data. For 300 to 700 atoms it gets a bit dodgier, and beyond 700 atoms you usually don't get enough redundancy for small molecule methods to work. It's really kind of arbitrary, though. I'd settle for 2000 MW as a boundary. It's as good an arbitrary limit as any.
10 posts • Page 1 of 1
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