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Biochemistry Alpha and Beta Glucose

Hi there!

I am having some difficulty with the structure of Alpha and Beta glucose in that when they form their respected polysaccharides (starch and cellulose), would you refer to the bonding all the way along per monosaccharide as a glycosidic bond?

Also, the reason that Beta glucose molecules have their structural integrity and strength in Cellulose is due to the 180o rotation per turn - forming hydrogen bonds. Though why can't alpha glucose rotate 180o and have the same effect, despite the C1 and C2 hydroxyl group reversal?
What makes beta glucose superior?

Many thanks. :smile:

Reply 1

Serine Soul

If an a-glucose were to be rotated at 180°, it wouldn't be able to form a glycosidic bond with the next a-glucose, as two OH groups would not be able to combine :smile:

Reply 2

MrHarry

Original post by enaayrah

If an a-glucose were to be rotated at 180°, it wouldn't be able to form a glycosidic bond with the next a-glucose, as two OH groups would not be able to combine :smile:

Ah, so the ability of Beta glucose to make 180o rotations per turn allows it to have hydrogen bonds which strengthen the structure? How exactly do the rotations make it superior in strength to form cellulose?

Thanks for replying :smile:

Reply 3

Serine Soul

Original post by MrHarry

Yeah, something along those lines. If you recall from chemistry, in the context of the glucose molecules, an OH group (with a lone pair of electrons in the O) must be present, as well as an δ+ hydrogen on the glucose molecule above.

I'm not too advanced on this kind of stuff, but I'm guessing the rotation allows the hydrogen bond to form in such a way :dontknow:

Reply 4

MrHarry

Thanks for replying, though I'm still rather confused. :-(
Im struggling with understanding how exactly the Beta Glucose rotations make its strength superior to that of Alpha glucose, and how exactly is Alpha glucose inferior?

(in that Beta glucose chains form a firm, strong and tensile cellulose whereas Alpha glucose chains form starch)

Reply 5

Mihir talsania

Original post by MrHarry

If the Beta Glucose is able to rotate 180 degrees it is able to form a glycosidic bond with another glucose molecules..Exactly what the previous person said.. What makes Beta glucose more superior to Alpha is that with its ability to rotate 180 degrees it is able to change the structure of the chain forming i.e. they will just not be forming a straight chain of polysaccharides/. Thus we say that the Alpha glucose molecule is able to only form a 1:4 bond with other glucose molecules ( this gives us only straight chains of glucose molecules) and Beta glucose molecules are able to form both 1:4 and 1:6 bonds with other glucose molecules. An example of Beta glucose bondings is found in Starch or cellulose. Just search up the structure of cellulose and you will get an idea of what i'm talking about. FYI when i mention 1:4 or 1:6 it means the carbon number the bond is forming between. E.g. 1:4 bond is a bond between the first carbon atom in the glucose molecule and the 4th carbon atom in another glucose molecule

Reply 6

streetlightppl

This is an old thread, but I'm studying this now for AS Bio - it's about the beta-glucoses forming straight chains rather than the alpha glucoses forming coils, so the straight chains of beta-glucoses can lie flat together, tightly packed, and form a strong structure of cellulose (there are hyrdogen bonds involved somewhere...) whereas the alpha chains are coiled so can't pack tightly together - they kinda make blobs of carbohydrate? Like the strach granules mentioned earlier. Hope this helps anyone looking at this now :biggrin:

Edit: starch uses alpha-1,4- and aplha-1,6-glycosidic bonds, but there are two different components of starch: amylose and amylopectin. The amylose is coiled and only uses alpha-1,4-glycosidic bonds, whereas amylopectin is branched/coiled along branches and uses alpha-1,4- and alpha-1,6-glycosidic bonds. Cellulose only uses beta-1,4-glycosidic bonds, where every other beta glucose molecule is rotated so it is more or less upside down.

(edited 5 years ago)

Reply 7

New Wonder

Original post by Mihir talsania

That's just wrong I am afraid. Alpha glucose can form 1,6 glycosidic linkages - it's why glycogen and starch can form branched chains.

Reply 8

username5360040

This is an old thread, but the reason why the rotated ß-glucose is that the subsequent arrangement from rotation makes hydrogen bonds between different chains possible. For alpha glucose molecules(which don't flip over) the OH groups are pointing inwards and these form hydrogen bonds with other glucose in the same chain. This results in the alpha helix, which is good for storage. However, for beta glucose, every alternate glucose rotates therefore some OH groups are facing inwards and some outwards. Thereby some of them forming hydrogen bonds with adjacent parallel chains, whose collective strength gives its structural stability. :smile: