1 / 23

GLYCOLYSIS

GLYCOLYSIS. For centuries, bakeries and breweries have exploited the conversion of glucose to ethanol and CO 2 by glycolysis in yeast. The fate of glucose molecule in the cell. Glucose. Pentose phosphate pathway supplies the NADPH for lipid synthesis and pentoses for nucleic acid synthesis.

shepry
Télécharger la présentation

GLYCOLYSIS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. GLYCOLYSIS For centuries, bakeries and breweries have exploited the conversion of glucose to ethanol and CO2 by glycolysis in yeast

  2. The fate of glucose molecule in the cell Glucose Pentose phosphate pathway supplies the NADPH for lipid synthesis and pentoses for nucleic acid synthesis Glycogenogenesis (synthesis of glycogen) is activated in well fed, resting state Glucose-6-phosphate Ribose, NADPH Glycogen Pyruvate Glycolysis is activated if energy is required

  3. Glycolysis is the earliest discovered and most important process of carbohydrates metabolism. Glycolysis – metabolic pathway in which glucose is transformed to pyruvate with production of a small amount of energy in the form of ATP or NADH. Glycolysis is an anaerobic process (it does not require oxygen). Glycolysis pathway is used by anaerobic as well as aerobic organisms. In glycolysis one molecule of glucose is converted into two molecules of pyruvate. In eukaryotic cells,glycolysis takes place in the cytosol.

  4. Acetyl CoA • Pyruvate can be further metabolized to: (1)Lactate or ethanol (anaerobic conditions) (2) AcetylCoA (aerobic conditions) • Acetyl CoA is further oxidized to CO2 and H2O via the citric acid cycle • Much more ATP is generated from the citric acid cycle than from glycolysis

  5. Catabolism of glucose in aerobic conditions via glycolysis and the citric acid cycle

  6. The glycolytic pathway consist of ten enzyme-catalyzed reactions that begin with a glucose and split it into two molecules of pyruvate

  7. Glycolysis (10 reactions) can be divided into three stages • In the 1st stage (hexosestage) 2 ATP are consumed per glucose • In the 3rd stage (triosestage)4 ATP are produced per glucose • Net: 2 ATP produced per glucose

  8. Stage 1, which is the conversion of glucose into fructose 1,6-bisphosphate, consists of three steps: a phosphorylation, an isomerization, and a second phosphorylation reaction. The strategy of these initial steps in glycolysis is to trap the glucose in the cell and form a compound that can be readily cleaved into phospho-rylated three-carbon units.

  9. Stage 2 is the cleavage of the fructose 1,6-bisphosphate into two three-carbon fragments dihydroxyacetone phosphate and glyceraldehyde 3-phosphate. Dihydroxyacetone phosphate and glyceraldehyde 3-phosphate are readily interconvertible.

  10. In stage 3, ATP is harvested when the three-carbon fragments are oxidized to pyruvate.

  11. Glycolysis Has 10 Enzyme-Catalyzed Steps 1. Hexokinase • Each chemical reaction prepares a substrate for the next step in the process • Transfers the g-phosphoryl of ATP to glucose C-6 oxygen to generate glucose 6-phosphate (G6P) • Four kinases in glycolysis: steps 1,3,7, and 10 • All four kinases require Mg2+ and have a similar mechanism

  12. Properties of hexokinases • Broad substrate specificity - hexokinases can phosphorylate glucose, mannose and fructose • Isozymes- multipleforms of hexokinase occur in mammalian tissues and yeast • Hexokinases I, II, III are active at normal glucose concentrations • Hexokinase IV (Glucokinase) is active at higher glucose levels, allows the liver to respond to large increases in blood glucose • Hexokinases I, II and III are allosterically inhibited by physiological concentrations of their immediate product, glucose-6-phosphate, but glucokinase is not.

  13. 2. Glucose 6-Phosphate Isomerase • Converts glucose 6-phosphate (G6P) (an aldose) to fructose 6-phosphate (F6P) (a ketose) • Enzyme preferentially binds the a-anomer of G6P (converts to open chain form in the active site) • Enzyme is highly stereospecific for G6P and F6P • Isomerase reaction is near-equilibrium in cells

  14. 3. Phosphofructokinase-1 (PFK-1) • Catalyzes transfer of a phosphoryl group from ATP to the C-1 hydroxyl group of F6P to form fructose 1,6-bisphosphate (F1,6BP) • PFK-1 is metabolically irreversible and a critical regulatory point for glycolysis in most cells • A second phosphofructokinase (PFK-2) synthesizes fructose 2,6-bisphosphate (F2,6BP)

  15. 4. Aldolase • Aldolase cleaves the hexose F1,6BP into two triose phosphates: glyceraldehyde 3-phosphate (GAP) and dihydroxyacetone phosphate (DHAP) • Reaction is near-equilibrium, not a control point

  16. 5. Triose Phosphate Isomerase (TPI) • Conversion of DHAP into GAP • Reaction is very fast, only the D-isomer of GAP is formed • Reaction is reversible. At equilibrium, 96% of the triose phosphate is DHAP. However, the reaction proceeds readily from DHAP to GAP because the subsequent reactions of glycolysis remove this product.

  17. Fate of carbon atoms from hexose stage to triose stage

  18. 6. Glyceraldehyde 3-Phosphate Dehydrogenase (GAPDH) • Conversion of GAP to 1,3-bisphosphoglycerate (1,3BPG) • Molecule of NAD+ is reduced to NADH • Energy from oxidation of GAP is conserved in acid-anhydride linkage of 1,3BPG • Next step of glycolysis uses the high-energy phosphate of 1,3BPG to form ATP from ADP

  19. 7. Phosphoglycerate Kinase (PGK) • Transfer of phosphoryl group from the energy-rich mixed anhydride 1,3BPG to ADP yields ATP and 3-phosphoglycerate (3PG) • Substrate-level phosphorylation - Steps 6 and 7 couple oxidation of an aldehyde to a carboxylic acid with the phosphorylation of ADP to ATP

  20. 8. Phosphoglycerate Mutase • Catalyzes transfer of a phosphoryl group from one part of a substrate molecule to another • Reaction occurs without input of ATP energy

  21. 9. Enolase: 2PG to PEP • 2-Phosphoglycerate (2PG) is dehydrated to phosphoenolpyruvate (PEP) • Elimination of water from C-2 and C-3 yields the enol-phosphate PEP • PEP has a veryhigh phosphoryl group transfer potential because it exists in its unstable enol form

  22. 10. Pyruvate Kinase (PK) PEP + ADP  Pyruvate + ATP • Catalyzes a substrate-level phosphorylation • Metabolically irreversible reaction • Regulation both by allostericmodulators and by covalentmodification • Pyruvate kinase gene can be regulated by various hormones and nutrients

  23. Net reaction of glycolysis During the convertion of glucose to pyruvate: • Two molecules of ATP are produced • Two molecules of NAD+ are reduced to NADH Glucose + 2 ADP + 2 NAD+ + 2 Pi 2 Pyruvate + 2 ATP + 2 NADH + 2 H+ + 2 H2O

More Related