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so it all ends up as glucose? is galactose processed through the liver or will it conceivably end up as muscle glycogen once turned into glucose? thanks.
so it all ends up as glucose? is galactose processed through the liver or will it conceivably end up as muscle glycogen once turned into glucose? thanks.
Correct. While UDP Glucose is the immediate precursor to glycogen and is involved in the glycogen synthase enzyme, I don't know the specific amount that is stored in the liver or muscle.
Hydrolysis of Disaccharides and Small Glucose Polymersinto Monosaccharides by Intestinal Epithelial Enzymes.The enterocytes lining the villi of the small intestinecontain four enzymes (lactase, sucrase, maltase, anda-dextrinase), which are capable of splitting the disaccharideslactose, sucrose, and maltose, plus other smallglucose polymers, into their constituent monosaccharides.These enzymes are located in the enterocytes coveringthe intestinal microvilli brush border, so that thedisaccharides are digested as they come in contact withthese enterocytes.Lactose splits into a molecule of galactose and amolecule of glucose. Sucrose splits into a molecule offructose and a molecule of glucose. Maltose and othersmall glucose polymers all split into multiple moleculesof glucose. Thus, the final products of carbohydratedigestion are all monosaccharides. They are all watersoluble and are absorbed immediately into the portalblood.After absorption from the intestinal tract, much of thefructose and almost all the galactose are rapidly convertedinto glucose in the liver.Therefore, little fructoseand galactose are present in the circulating blood.Glucose thus becomes the final common pathway for thetransport of almost all carbohydrates to the tissue cells.In liver cells, appropriate enzymes are available topromote interconversions among the monosaccharides—glucose, fructose, and galactose—as shown inFigure 67–3. Furthermore, the dynamics of the reactionsare such that when the liver releases the monosaccharidesback into the blood, the final product is almostentirely glucose.The reason for this is that the liver cellscontain large amounts of glucose phosphatase. Therefore,glucose-6-phosphate can be degraded to glucose and phosphate, and the glucose can then be transportedthrough the liver cell membrane back into the blood.Once again, it should be emphasized that usuallymore than 95 per cent of all the monosaccharides thatcirculate in the blood are the final conversion product,glucose.Carbohydrate MetabolismIn carbohydrate metabolism, the liver performs the followingfunctions, as summarized from Chapter 67:1. Storage of large amounts of glycogen2. Conversion of galactose and fructose to glucose3. Gluconeogenesis4. Formation of many chemical compounds from intermediate products of carbohydrate metabolismDoes this help? Taken from Textbook of Medical Physiology (Fifth Edition).
Exactly what I was looking for. So Galactose (half of all lactose) follows the same pathway as fructose.are/were you a nutrition student?
I minored in Nutrition, but I didn't really get a lot out of it in college. I majored in Exercise Science, and got my CSCS, but I still like to learn what's going on with nutrition and exercise to keep current on new research. Pretty soon I will be going back to school for endocrinology or physical therapy here soon. Should have done that one before, but alas hindsight is always 20/20. Eh?
Exactly what I was looking for. So Galactose (half of all lactose) follows the same pathway as fructose.are/were you a nutrition student?
Fructose does not use the Leloir pathway, so it is not the same pathway.
Yeah, fructose is all by itself. It's one of those quirky sugars. I believe it can only get digested in the liver, the only problem is that it skips a key rate limiting enzyme, either glucokinase or hexokinase (I believe both of these are interchangeable, but one resides predominately in the tissues and one in the liver) and goes right into glycolysis–regardless of whether there's ATP-glycogen available. So fructose can be processed by the body without any sort of indication of where to go. Fructose doesn't stimulate a insulin response, so it doesn't trigger CCK or any hormones to control hunger, so you can just keep eating and never feel full, with energy piling up in the tissues.The name of the catalyst that primes this escapes me at the moment, but I think it is phosphofructokinase fructose -> portal vein -> liver -> glycolysis -> (then if it isn't stored as glycogen) it can fall off the chain in the Kreb's Cycle from Citrate -> Fatty Acids (up along the chain).
Yeah, fructose is all by itself. It's one of those quirky sugars. I believe it can only get digested in the liver, the only problem is that it skips a key rate limiting enzyme, either glucokinase or hexokinase (I believe both of these are interchangeable, but one resides predominately in the tissues and one in the liver) and goes right into glycolysis--regardless of whether there's ATP-glycogen available. So fructose can be processed by the body without any sort of indication of where to go. Fructose doesn't stimulate a insulin response, so it doesn't trigger CCK or any hormones to control hunger, so you can just keep eating and never feel full, with energy piling up in the tissues.The name of the catalyst that primes this escapes me at the moment, but I think it is phosphofructokinase fructose -> portal vein -> liver -> glycolysis -> (then if it isn't stored as glycogen) it can fall off the chain in the Kreb's Cycle from Citrate -> Fatty Acids (up along the chain).
Spot on. I know hexokinase phosphorylates fructose to its 6-phosphate form or in the liver fructokinase phosphorylates fructose to the 1-phosphate form. I'm not certain as to glucokinase necessarily having zero affinity for fructose (I believe it is theoretically possible) but that at the levels of each found in the body little such enzymatic activity occurs.
From what I've researched glucokinase only acts upon glucose in the liver. It has no effect on fructose at all. It doesn't need to, fructose goes straight in through the glycolytic process. Check out the below flow chart…I really like this one.
From what I've researched glucokinase only acts upon glucose in the liver. It has no effect on fructose at all. It doesn't need to, fructose goes straight in through the glycolytic process. Check out the below flow chart...I really like this one.
Sorry, I should have been more explicit in what I meant. I was just trying to make sure that it was clear not that glucokinase doesn't "ignore" other hexose substrates but that the cellular concentrations simply do not exist for that particular enzymatic phosphorylation to occur.Great chart.
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