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Glycolysis ط Steps and key enzymes for glycolysis (irreversible reactions) ط Dual role of glycolysis; degrades glucose to generate ATP and source of synthesis.

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Presentation on theme: "Glycolysis ط Steps and key enzymes for glycolysis (irreversible reactions) ط Dual role of glycolysis; degrades glucose to generate ATP and source of synthesis."— Presentation transcript:

1 Glycolysis ط Steps and key enzymes for glycolysis (irreversible reactions) ط Dual role of glycolysis; degrades glucose to generate ATP and source of synthesis of cell compounds ط Aerobic and Anaerobic glycolysis, Pyruvate and lactate as end products of glycolysis ط Calculation of energy and Inhibitors of glycolysis ط Clinical correlation * Lactic acidosis D

2 Introduction fig7.4, Glycolysis occur in all cells 1. RBCs (anaerobic) – GLUT1: NADPH (PPP), Lactate 2. Brain (aerobic) – GLUT3: NADPH (PPP), CO2+H2O 3. Muscle (both) – GLUT4: CO2+H2O, Lactate, Glycogen 4. AT (aerobic) – GLUT4: NADPH (PPP), Glycogen, FA 5. Liver (both) – GLUT2: NADPH (PPP), Glycogen, FA, Lactate, Glucose, Glucurinides *NADPH for glutathione (organic peroxide, H 2 O 2 ), FAS, Endoplasmic Reticulum, Ribose Phosphate (ATP, DNA, RNA)

3 Glycolysis fig7.6, (+8 ATP)fig Priming Stage: (–2 ATP) Step1: Glu ===  G6P Step2: G6P  F6P (by open chain) Step3: F6P ===  F1,6P2 *F6P  PFK2 (–1 ATP)  F2,6P 2 2. Splitting Stage: (2 GAP) Step4: F1,6P2  DHAP + GAP (by splitting 3C each) Step5: DHAP  GAP 3. Oxidative-phosphorylation Stage: (+10 ATP) Step6: GAP  1,3BPG fig7.7, substrate-level phosphorylation: oxid-reduct (thiohemiacetal, Energetic) = +6 ATP Step7: 1,3BPG  3PG (through BPG shunt, no ATP formed in 15-25% of RBCs) *1,3BPG  2,3BPG M-tase  2,3BPG  2,3BPG P-tase  3PG Step8: 3PG  2PG Stpe9: 2PG  PEP Step10: PEP ===  Pyruvate End product: i. Anaerobic Glycolysis; Pyruvate  LDH  2 Lactate LDH utilize NADH to form Lactate … but fig7.9, cytoplasmic NADH when Pyruvate is formed enter mitochondria: a. GP shuttle (muscle) to generate FADH2 (mitochondrial membrane) b. MA shuttle (liver) to generate NADH (mitosol) ii. Aerobic Glycolysis; 2 Citric Acid Cycles (CO 2 + H 2 O, complete glu oxid) *Fermentation; in yeast (Ethanol + CO 2 )

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8 Inhibitors of Glycolysis 1. fig7.10, Deoxyglucose: doGlucose  HK  doG6P doG6P inhibit HK but is not a substrate (accumulate in cell) 2. fig7.11, Sulfhydryl Reagent (mercury, iodoacetate): GAP  GAPDH (+NADH)  1,3BPG mercury binds to –SH of GAPDH & prevents Thiohemiacetal formation, no NADH is formed 3. Fluoride (F): 2PG  Enolase  PEP fluoride bind to Mg2+/Pi forming an ionic complex, which interferes with enolase binding 4. fig7.12, Arsenate: GAP  GAPDH (+NADH)  1,3ABPG  PGK (+ATP)  3PG replaces Pi when 1,3BPG is formed, therefore no ATP is yielded when 3PG is formed Arsenic: substitutes Pi & product accumulates (no further ATP produced by glycolysis or TCA cycle)

9 Regulation of Glycolysis, Oxidation of other monosaccharides ط Regulation of glycolysis (at cellular level), irreversible steps ط Comparison of hexokinase and glucokinase ط Factors affecting glycolysis ط Entry of fructose, galactose and mannose into glycolysis ط Clinical correlation: * Lactose intolerance * Fructose intolerance * Galactosemia D , L

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11 Regulation (irreversible or non-equilibrium reactions) Glucokinase (HK 4) fig 7.14 Hexokinase (HK 1, 2, 3) 1. In liver & pancreatic b-cells 2. high Km & low affinity for glucose (~10mM) 3. Acts only on D-Glu (diet) 4. Inducible Enzyme (Glu, F1P by release from GKRP, INS through gene expression) 5. Inhibited by F6P (by binding to GKRP) 6. Acts on Glu, in response to high Glu concentration following a meal, to remove Glu from blood. 1. In most Tissues 2. Low Km & high affinity for glucose (<0.1mM) 3. Acts on D-Glu & other hexoses ( e.g. α-Glu & β-Glu) 4. Constitutive Enzyme (continuous activity) 5. Inhibited by G6P (Allosteric) 6. Acts at low Glu concentration to ensure supply of Glu to other tissues (especially Brain). Thereby maintain concentration gradient between blood & intracellular environment 1. HK (low Km) / GK (high Km) ….. Table * different kinetics!!Table a) HK: + INS (Glu-R) – G6P (G6P-tase) b) GK: + INS (gene expression) + F1P (GKRP) – F6P (GKRP)

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13 2. PFK1: rate-limiting enzyme (F6P  PGI-ase (reversible)  G6P  Glu, Gly, PPP a) ATP / AMP ratio (energy): 2ADP  AK  ATP + AMP; ↓ ATP  ↑↑ AMP + ↑↑ ADP by + PFK1 (F6P  F1,6P2) / – F1,6P2-tase (F1,6P2  F6P) b) Fig7.17 Cell Environment (cytosolic): · More H+ ions (low pH): Glu (bld)  GLUT (membrane)  Glycolysis (anaerobic)  2 Lact + 2 H+ (cytosol)  symport (membrane)  2 Lact + 2 H+ (bld) · Balance between Lact Prod : Lact Utilize 2 Lact  LDH  Pyr  Glu, Gly, PPP c) Tissues use other fuels (KB/FA) to preserve Glu for brain: citrate (TCA cycle, mitosol)  don't complete TCA cycle  go to cytosol (– glycolysis)  KB/FA oxidation (mitosol) d) Fig7.19 INS/GLG: · F2,6P2 promotes glycolysis & inhibit gluconeogenesis by + PFK1, – F1,6P2-tase *F1,6P2  F1,6P2-tase  F6P  PFK1  F1,6P2 · fig7.25, in LIVER § GLG  ↑ cAMP  ↓ F2,6 P2-tase  inhibit glycolysis by – PFK1, + F1,6P2-tase § fig 7.21, F2,6P2  F2,6P2-tase  F6P  PFK2  F2,6P2fig 7.21

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15 fig7.24fig7.24, PFK2 a/F2,6P 2 -tase b  PK-A  PFK2 b/F2,6P2-tase a cAMP inhibit glycolysis & promotes gluconeogenesis by + PK-A  + F2,6P 2 -tase, – PFK2 § fig7.27, INS promotes glycolysis by i. + cAMP PDE-ase (↑ AMP) : cAMP  cAMP PDE-ase  AMP ii. + PP-tase: PFK2 b/F2,6P2-tase a  PFK2 a/F2,6P2-tase b iii.– PK-A: PFK2 a/F2,6P 2 -tase b  PFK2 b/F2,6P2-tase a · Fig7.28, in HEART § Epineph acts on PK-A, which acts opposite of liver (to ↑ ATP)

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17 3. PyrK: has high Km as GK (need high substrate concentration in diet / INS) a) fig7.30, PyrK a  PK-A  PyrK b  PP-tase  PyrK afig7.30 b) cAMP (GLG) promotes + PK-A: PyrK a "active" è PyrK b "inactive" c) F1,6P2 (PFK1) promotes + PP-tase: PyrK b "inactive" è PyrK a "active" d) PyrK is inhibited (–) by ATP, alanine * GLG inhibit PyrK by promoting gluconeogenesis

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19 Clinical Correlation 1. fig7.17, Lactic Acidosis cc7.5 a. increase in Lact Prod: Excessive exercise, convulsions, Angina, Pulmonary Failure  ↓bld circulation  ↓O2 to cell  ↑Lact + H+ in bld b. decrease in Lact Utilize: Liver diseases, ethanol, Phenformin (drug)  ↓gluconeogenesis + ↓TCA cycle + ↓O2 to cell è ↑Lact + H+ in bld 2. fig, Fructose Intolerance cc7.3 Fru  FK  F1P  F1Paldolase  DHAP + GAP a. deficiency in F1Paldolase lead to F1P accumulate  deplete of Pi & ATP  Osmotic lysis b. deficiency in FK is less important (Fru  F6P or Sucrose) 3. fig, Galactosemia cc8.3 Gal  GalK  Gal1P  Gal1PUT-ase  UDP-Gal  UDP-Glu  Galctitol a. deficiency in GalK inhibit Gal to Glu drived from Lactose (cataract, CNS damage) b. deficiency in Gal1PUT-ase accumulates Gal1P (liver damage)

20 Clinical Correlation 2. fig, Fructose Intolerance cc7.3 Fru  FK  F1P  F1Paldolase  DHAP + GAP a. deficiency in F1Paldolase lead to F1P accumulate  deplete of Pi & ATP  Osmotic lysis b. deficiency in FK is less important (Fru  F6P or Sucrose)

21 Clinical Correlation 3. fig, Galactosemia cc8.3 Gal  GalK  Gal1P  Gal1PUT-ase  UDP-Gal  UDP-Glu  Galctitol a. deficiency in GalK inhibit Gal to Glu drived from Lactose (cataract, CNS damage) b. deficiency in Gal1PUT-ase accumulates Gal1P (liver damage)


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