August 26, 2009 at 5:58 am #11734teyyaParticipant
hi all.i need to ask some questions…because it was asked by my lecture…in glycolysis process,why glucose cannot be phosphorylated two times and directly converted to glucose-1,6 biphosphate instead of fructose 1,6 biphoshpate?..and secondly, can galactose be transformed to fructose? i need ur help……
August 26, 2009 at 10:01 am #92600mandeParticipant
Since I have yet to learn about phosphorylation, I can only answer your second question about ‘the transformation of galactose to fructose’.
If I’m not mistaken, no, galactose cannot be transformed/converted to fructose (a sugar found in fruits). This is because both the aforementioned are monosaccharides.
a) glucose + glucose => maltose
b)glucose + galactose => lactose
c) glucose + fructose => sucrose
On another note, these two simple sugars are likely to compete with each other in a certain condition as such I have read on Wikipedia.
"Fructose absorption occurs via the GLUT-5 (fructose only) transporter, and the GLUT2 transporter, for which it competes with glucose and galactose. A deficiency of GLUT 5 may result in excess fructose carried into the lower intestine. There, it can provide nutrients for the existing gut flora, which produce gas. It may also cause water retention in the intestine. These effects may lead to bloating, excessive flatulence, loose stools, and even diarrhea depending on the amounts eaten and other factors."
I know the last part may not be of help but I hope I have helped in some way! And if i’m wrong, then feel free to correct me because there is learning through mistakes!
August 29, 2009 at 2:36 pm #92645MrMisteryParticipant
monosaccharides can be converted into one other, otherwise you could never utilize any other sugar than fructose or glucose. Galactose for example can be converted to glucose via Galactose-1-phosphate uridyl transferase. fructose can be phosphorylated by fructokinase, from where it enters the glycolysis pathway, which can then generate glucose by running in reverse.
Of yeah and the stuff about transporters has nothing to do with the metabolism part.
As for the first question, I can only guess that it is a more favorable reaction to phosphorylate a hydroxyl group on the chain (carbon 1) in a ketose sugar than any of the hydroxyl groups inside the ring of an aldose sugar (aldose sugars like glucose do not have a hydroxyl group on Carbon 1 and have a carbonyl group instead. You need a hydroxyl group to create the phosphoester bond during the phosphorylation reaction).
August 31, 2009 at 3:17 pm #92654teyyaParticipant
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