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Section J carbohydrate metabolism

Section J carbohydrate metabolism. Monosaccharides and disaccharides Polysaccharides and oligosaccharides Glycolysis Citric acid synthesis Carbohydrate Biosynthesis Pentose phosphate pathway. J1 Monosaccharides and disaccharides. Aldoses and ketoses.

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Section J carbohydrate metabolism

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  1. Section Jcarbohydrate metabolism • Monosaccharides and disaccharides • Polysaccharides and oligosaccharides • Glycolysis • Citric acid synthesis • Carbohydrate Biosynthesis • Pentose phosphate pathway

  2. J1 Monosaccharides and disaccharides

  3. Aldoses and ketoses A monosaccharide has the general formula (CH2O)n and contains either an aldehyde group (an aldose) or a ketone group (a ketose).

  4. Stereoisomers The D and L stereoisomers of sugars refer to the configuration of the asymmetric carbon atom furthest from the aldehyde or ketone group.

  5. Aldoses

  6. (赤藓糖）

  7. 阿拉伯糖 木糖

  8. 葡萄糖 甘露糖 半乳糖

  9. Ketoses

  10. Ring structure Tetroses and larger sugars can cyclized by reaction of the aldehyde or ketone group with a hydroxyl group on another carbon atom of the sugar.

  11. A monosaccharide is called a reducing sugar.

  12. disaccharides A disaccharide is formed when two monosaccharides become joined by a glycosidic bond.

  13. Sugar derivatives The hydroxyl groups of sugars can be replaced by other groups to form a wide range of biologically important molecules including phosphorylated sugars, amino sugars and nucleotides.

  14. nomenclature The names of simple sugars and sugar derivatives can all be abbreviated. Glc glucose Fru fructose

  15. J2 Polysaccharides and oligosaccharides Long chains of monosacharides joined together are collectively called polysaccharides. The major storage polysaccharides are glycogen, starchand dextran. Cellulose is a structural polysaccharide found in plant cell wall.

  16. Carbohydrate metabolism (Section J3---Glycolysis) Glycolysis comes from the Greek glykys, meaning “sweet”, and lysis, meaning “splitting”.

  17. An overview on D-glucose metabolism • The major fuel of most organisms, G'o = –2840 kJ/mole if completely oxidized to CO2 and H2O via the glycolysis pathway, citric acid cycle and oxidative phosphorylation (generating ATP) . • Can also be oxidized to make NADPH and ribose-5-P via the pentose phosphate pathway. • Can be stored in polymer form (glycogen or starch) or be converted to fat for long term storage. • Is also a versatile precursor for carbon skeletons of almost all kinds of biomolecules, including amino acids, nucleotides, fatty acids, coenzymes and other metabolic intermediates.

  18. 1. The Development of Biochemistry and the Delineation of Glycolysis Went Hand by Hand • 1897, Eduard Buchner (Germany), accidental observation : sucrose (as a preservative) was rapidly fermented into alcohol by cell-free yeast extract. • The accepted view that fermentation is inextricably tied to living cells (i.e., the vitalistic dogma) was shaken and Biochemistry was born: Metabolism became chemistry! • 1900s, (Arthur Harden and William Young) Pi was needed for yeast juice to ferment glucose, a hexose diphosphate (fructose 1,6-bisphosphate) was isolated.

  19. 1900s, Arthur Harden and William Young (Great Britain) separated the yeast juice into two fractions: one heat-labile, nondialyzable zymase (enzymes) and the other heat-stable, dialyzable cozymase (metal ions, ATP, ADP, NAD+). • 1910s-1930s, Gustav Embden and Otto Meyerhof (Germany), studied muscle and its extracts: • Reconstructed all the transformation steps from glycogen to lactic acid in vitro; revealed that many reactions of lactic acid (muscle) and alcohol (yeast) fermentations were the same! • Discovered that lactic acid is reconverted to carbohydrate in the presence of O2 (gluconeogenesis); observed that some phosphorylated compounds are energy-rich.

  20. (Glycolysis was also known as Embden-Meyerhof pathway). • The whole pathway of glycolysis (Glucose to pyruvate) was elucidated by the 1940s.

  21. 2. The overall glycolysis can be divided into two phases • The hexose is first phophorylated (thus activated) and then cleaved to produce two three-carbon intermediates at the preparatory phase, consuming ATP. • The three-carbon intermediates are then oxidized during the payoff phase, generating ATP and NADH.

  22. Group transfer Isomerization Group transfer cleavage Isomerization

  23. Dehydrogenation Group transfer Group shift Dehydration Group transfer

  24. 3. Ten enzymes catalyze the ten reactions of glycolysis • Hexokinase (also glucokinase in liver) catalyzes the first phosphorylation reaction on the pathway. • Phosphohexose isomerase (also called phosphoglucose isomerase) catalyzes the isomerization from glucose 6-P to fructose 6-P, converting an aldose to a ketose.

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