Lecture 19 to 22 Metabolism New

Lecture 19 to 22 Metabolism New - Lecture 19 to 22...

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Lecture 19-22: Carbohydrate, Lipid and Amino acids Metabolism Carbohydrate metabolism: Absorption of carbohydrate: Most of the monosaccharides (mainly glucose, fructose and galactose) from diet have been transported across basolateral side of enterocyte in intestine. Monosaccharides are absorbed into the portal vein and then transport to the liver. Liver takes a portion, accounts for about 30-35% of ingested glucose from a meal, ships excess out to the tissues. Liver takes up almost all of the fructose and galactose from the portal vein. Circulating levels of fructose are very low, but some can get to muscles when large amounts of fructose are consumed. Carbohydrate reserves in a 70 kg person Liverglycogen 72 g Muscle glycogen 245 g Circulating glucose 10 g Enough to last for 10-18 h of fasting
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1. Glucose a) Glycolysis b) Glycogen synthesis/breakdown c) gluconeogenesis 1. Fats/triacylglycerols a) Lipolysis b) Fatty acid synthesis c) Triacylglycerol synthesis 2. Amino acids/proteins a) Protein breakdown b) Amino acid breakdown c) Amino acid synthesis What happen after a full meal/Starving?
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The sodium ions are pumped back out of the cell by the Na+/K+ ATPase in order to maintain their concentration gradient. Glucose cross the plasma membrane of the intestinal cells using a Na+/glucose transporter which allows sodium ions and glucose to enter the cell together ( that is, both molecules are passing trough the membrane in the same direction: symporter ). The sodium ions flow down their concentration gradient while the glucose molecules are pumped up theirs gradient. Glucose is then released into the bloodstream by a glucose transporters ( Eg. GLUT 2 in enterocyte is uniport transporter while Glut-1/Glut-5 in other tissues is bidirectional transporter) present in the basal membrane of the endothelial cells
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Salient characteristics of the hexose transporters are summarized in the table below. Transporter Major Sites of Expression Characteristics SGLUT 1 Intestinal mucosa, kidney tubules Cotransports one molecule of glucose or galactose along with two sodium ions. Does not transport fructose. GLUT-1 Brain, erythrocyte, endothelial cells, fetal tissues Transports glucose (high affinity) and galactose, not fructose. Expressed in many cells. GLUT-2 Liver, pancreatic beta cell, small intestine, kidney. Tranports glucose, galactose and fructose. A low affinity, high capacity glucose transporter; serves as a "glucose sensor" in pancreatic beta cells. GLUT-3 Brain, placenta and testes Transports glucose (high affinity) and galactose, not fructose. The primary glucose transporter for neurons. GLUT-4 Skeletal and cardiac muscle, adipocytes The insulin-responsive glucose transporter. High affinity for glucose. GLUT-5 Small intestine, sperm Transports fructose, but not glucose or galactose. Present also in brain, kidney, adipocytes and muscle.
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Uptake of glucose into hepatocyte: Via cell membrane transporter GLUT (Glucose transporter for facilitate diffusion): are bidirectional; they can transport glucose both into and out of cells.
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This note was uploaded on 07/04/2011 for the course BIOC Point taught by Professor Point during the Spring '11 term at HKU.

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Lecture 19 to 22 Metabolism New - Lecture 19 to 22...

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