Relationship between structure and function of glucoes

[ccBiologist]

Ok what is the relationship between the structure and function of glucose? i have read so far that the hydrogens found in glucose are removed and used to regenerate ATP from ADP + P. Im not so certain about that anyone care to help?

[JackBean]

the importance of structure of glucose will be seen, if you compare it with other monosaccharides

[greatmicrobiologist]

Go through the glycolysis. If you through the carbohydrate metabolism then you will understand the structural functions of each monosaccharide.

[ccBiologist]

Ok i went through glycolysis however for the record is it biologically correct to say that due to its structure glucose it can be easily oxidized to pyruvate in comparison to other monosaccharids which is used to produce energy via conversion of adp to atp

[ccBiologist]

however one question thoughwhat aspect of the structural formual would attribute to itbeing easily converted to pyruvate

[JackBean]

this is rather question, why did glucose become the main energy source and not e.g. mannose. That's similar to the question, why are we composed from L-amino acids

[Adz795]

Is there a possibility that the enzymes are specialized only for utilizing α-D-glucose and not its epimers like mannose,etc.?

Is the reason for us being composed of L-amino acids similar to the reason for α-D-glucose to form glycogen and not cellulose (ie because of it's ability to link and cross-link due to the -OH)? I mean the reason for only L-amino acids should be their way of linking. Am I correct?

[JackBean]

where did you get, that D-glc doesn't form cellulose?

If you studied the glycolysis, you should know the specifities of respective enzymes. Anyway, they are usually speciallied with the exception of hexose kinase. The other monosacharides must be first converted to Glc or Fru

[jonmoulton]

OK, I need to review a bit to get back in the carbohydrate saddle (oh wait, it's a chair). The α- in α-D-glucose is only really defined when the D-glucose is bound into a larger molecule. The bond out of glucose is in the α form in glucose and the β form in starch, but as a monomer bulk D-glucose in aqueous solution is not firmly in either α or β form (though one molecule, at one instant, if bound in a ring, will be in either α or β form). As a monomer, glucose is in equilibrium with a free aldehyde form. When the aldehyde reacts intramolecularly to form a closed ring, the resulting ring will be in α or β form depending on which face the carbonyl carbon (C1) forms the ring-closing bond. However, free D-glucose is a mixture of α and β forms and they are dynamically interconverting though the free aldehyde form. When the glucose is bound into a polymer, this locks the position of the ring-closing bond into either the α or β form. Galactose is pure 1-4 α-bound glucose while starch is a polymer of the pure 1-4 β form (though they may also have 1-6 linkages). Now I can look at your question again, Adz.

The α and β forms of poly-D-glucose have different mechanical properties and adopt different confirmations, with poly-α-D-glucose forming curving fibers and poly-β-D-glucose forming linear fibers (as you wrote, Adz, due to different hydrogen-bonding geometries). I don't think there is a similar logic to the L- vs. D- amino acids. I'm now speculating: I think that a simple protein composed entirely of D amino acids would be a mirror image of the same protein composed entirely of L amino acids and would have identical mechanical properties (except for properties like optical rotation), unlike the case for α versus β poly-D-glucose. Therefore the "choice" of L amino acids is not due to a property of their linking or the structures they form, but is an apparently arbitrary characteristic of terrestrial amino acids, perhaps an ancient accident of chance. Can anyone confirm or refute that?

[Adz795]

Oh yes! What a confusion I caused!
The difference in L-, D- properties would, in no way, originate from linking patterns (like in the case of α vs. β D-glucose). It would have to, as Jonmoulton speculated, originate from the fact that they are mirror images of each other. The reason for differences in α vs. β D-glucose is entirely different. It is because of the way the carbonyl carbon is bonded to the oxygen of the sixth carbon.

I apologize for causing this needless confusion.

I think I have one more question, Jonmoulton.
Starch is a poly-α-D-glucose. Cellulose is a poly-β-D-glucose. Am I correct?
I am do not understand why you said that "starch is a polymer of pure 1-4 β form". I understand that you mean the 1-4 glycosidic linkages are formed from the β form of glucose, but isn't that the α form?

And thanks a lot for answering me!

[jonmoulton]

Hi Adz,

You get me to review some carbohydrate chemistry, which I enjoyed (that's not the area I work in now). However, I made some errors (noted below).

Both starch and cellulose are primarily linked though 1-4 bonds. The difference is whether the bond to carbon 1 goes "up" or "down" relative to the ring. If there are any 1-6 bonds these cause branching -- these branches are common in starch.

I wrote "Galactose is pure 1-4 α-bound glucose while starch is a polymer of the pure 1-4 β form" Oops. That should have been:
Starch is pure 1-4 α-bound glucose while cellulose is a polymer of the pure 1-4 β form.

Sorry about that. Like I said, this isn't what I've been doing lately, but that's pretty darn sloppy on my part.

[Adz795]

Yes, that's just the correction I thought of.
Thanks so much! Feels good to be clear about it.