1-Biosynthesis of Carbohydrates-.pdf - BIOSYNTHESIS OF...

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BIOSYNTHESIS OF CARBOHYDRATES Assoc. Prof. Özlem Dalmızrak Near East University Faculty of Medicine Department of Biochemistry
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Energy storage in tissues, kcal Organ Glucose or glycogen Proteins Triacylglycerol Blood 60 0 45 Liver 400 400 450 Brain 8 0 0 Striated muscle 1,200 24,000 450 Adipose tissue 80 40 135,000 GLUCONEOGENESIS
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Human metabolism consumes about 160 ± 20 grams of glucose per day, about 75% of this in the brain. Body fluids carry only about 20 grams of free glucose, and glycogen stores normally can provide only about 180 to 200 grams of free glucose. Thus, the body carries only a little more than a one-day supply of glucose. If glucose is not obtained in the diet, the body must produce new glucose from noncarbohydrate precursors. The term for this activity is gluconeogenesis , which means the generation ( genesis ) of new ( neo ) glucose.
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Why do we make glucose? It is necessary to keep blood glucose concentration in a narrow range. Energy metabolism of some tissues brain, erythrocytes, testis and mammary mainly depends on glucose. Even though ketone bodies can be used in starvation, at physiological conditions glucose has vital importance for brain. Glucose is the only fuel molecule for erythrocytes. In addition to dietary glucose, sometimes gluconeogenesis provides glucose. GLUCONEOGENESIS
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Carbohydrate Synthesis From Simple Precursors: Gluconeogenesis
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Gluconeogenesis occurs in all animals, plants, fungi and microorganisms. The reactions are essentially same in all tissues and species. The precursors of glucose: lactate from muscle, forms pyruvate some amino acid carbon skeletons - from diet or breakdown of muscle protein during starvation- most important is alanine TCA cycle intermediates propionate from breakdown of TG and amino acids. glycerol from certain lipids. In mammals, it occurs primarily in the liver and to a lesser extent in renal cortex and epithelial cells that line the inside of the small intestine . GLUCONEOGENESIS
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GLUCONEOGENESIS
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Citric Acid Intermediates and Some Amino Acids Are Glucogenic
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Mammals cannot convert fatty acids to glucose. Pyruvate dehydrogenase reaction is irreversible. Plants, yeast and many bacteria have glyoxylate pathway to make glucose from acetyl-CoA. This is important during the germination of seedlings, before leaves develop and photosynthesis can provide energy and carbohydrates. The seedling relies on stored seed oils for energy production and cell wall biosynthesis. GLUCONEOGENESIS
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