Element 5; Lecture 4 Carbohydrate Metabolism Glycolysis Ms. K. Rohini Lecturer - FoM

Learning Objectives  Reactions of Glycolysis  Regulation of Glycolysis  Oxidation of pyruvate  Importance of acetyl CoA 31 Jan 2012Ms.Rohini FoM 2

Glucose  The “sugar” carried by blood  Energy fuel for all cells of the body – all cells depend on at least a small proportion of glucose for energy – some cells depend predominantly on glucose for energy (Eg.Brain) – some cells depend exclusively on glucose for energy (Eg.RBCs)

Glucose  Reaction for catabolism: Glycolysis  Reaction for anabolism: Gluconeogenesis

 Embden Meyerhof Pathway  Glykys – Sweet; lysis- splitting  Pathway is meant for Provision of energy 31 Jan 2012Ms.Rohini FoM 5 Glycolysis

Oxidation of glucose or glycogen to pyruvate or lactate Site: All cells of the body Subcellular site: Cytoplasm

Features  Major pathway of utilization of glucose in all cells  A CYTOSOLIC energy yielding pathway  Can operate in PRESENCE of or ABSENCE of OXYGEN (Aerobic or anaerobic glycolysis respectively)

Carbohydrate Metabolism Overview glycogen pentose GLUCOSE other sugars pyruvate lactate acetyl CoA EtOH TCA cycle ETS ATP

31 Jan 2012Ms.Rohini FoM 9

Glucose Glucose 6-phosphate Fructose 6-phosphate Fructose 1,6 bisphosphate Hexokinase / Glucokinase Mg 2+ ATP ADP ATP Phosphohexose isomerase Phosphofructokinase 1 (PFK-1) Mg 2+

Glyceraldehyde 3-phosphate Dihydroxyacetone phosphate 1,3-bisphosphoglycerate Fructose 1,6 bisphosphate Aldolase A NAD + NADH + H + Pi Triosephosphate isomerase Glyceraldehyde 3-phosphate dehydrogenase

1,3-bisphosphoglycerate 3-phosphoglycerate 2-phosphoglycerate Phosphoenolpyruvate Phosphoglycerate kinase Mg 2+ ADP ATP H2OH2O Phosphoglycerate mutase Enolase

Phosphoenolpyruvate Pyruvate CO2 + H 2 O + ATP Lactate Pyruvate kinase Mg 2+ ADP ATP Aerobic Lactate dehydrogenase Anaerobic NAD + NADH + H + (via PDH complex, TCA cycle, ETC)

Hexokinase Found in extrahepatic tissues Low Km, low Vmax for glucose Product inhibition by Glucose 6-phosphate Constitutive enzyme; non inducible Glucokinase Found in liver, -cells of pancreas High Km, high Vmax for glucose No product inhibition by glucose 6-phosphate Inducible by Insulin

Energetics Reaction ATP used ATP produced AerobicAnaerobic Hexokinase1-- Phosphofructokinase1-- Glyceraldehyde 3- phosphate D.H. -3x2 = 6- Phosphoglycerate kinase -1x2 = 2 Pyruvate kinase-1x2 = 2 Total2104 Total ATPs produced104 Net ATPs produced10-2 = 8 ATPs4-2 = 2 ATPs

Summary  Glycolysis – 10 steps  Key enzymes – Steps 1, 3, 9 = Irreversible  Energy Production – Steps 5,6,9  Regeneration of NAD+ - Steps 5 and 10

Regulation of glycolysis Three regulatory reactions: 1.Hexokinase/glucokinase 2.Phosphofructokinase 1 3.Pyruvate kinase

Regulation:  Hexokinase: inhibited by glucose 6-phosphate (end product inhibition/feedback inhibition)  Phosphofructokinase 1: − Activated by AMP, fructose 2,6 bisphosphate − Inhibited by citrate, ATP  Pyruvate kinase: − Activated by fructose 1,6 bisphosphate (feed-forward activation) − Inhibited by ATP, alanine  Fructose-2,6-Bisphosphate: Glycolysis favored

19 Metabolic Fates of Pyruvate Glucose Glycolysis Pyruvate Transamination Alanine Carboxylation Oxaloacetate Oxidative decarboxylation Acetyl Co A Reduction Lactate Oxidation CO 2 and H 2 O

20 Oxidative Decarboxylation of Pyruvate Under aerobic condition, pyruvate is oxidatively decarboxylated to acetyl CoA. Enzyme involved is pyruvate dehydrogenase, a multi-enzyme complex made up of three enzymes. Mitochondrial enzyme. Hence, pyruvate formed in cytosol is transported into mitochondrion by a pyruvate carrier. Reaction under physiological conditions is irreversible and yields acetyl CoA, CO 2 and NADH. Thiamine (B 1 ) → Riboflavin (B 2 ) → Niacin → Panthothenic acid →  Reaction requires coenzymes, derivatives of water-soluble vitamins; hence reaction affected by deficiency of these vitamins. Vitamin (?) →

21 Formation of Acetyl CoA from Pyruvate CH 3 -C-COO -  O Pyruvate CH 3 -C~S-CoA  O Acetyl CoA Pyruvate Dehydrogenase (PDH) Complex CoASH CO 2     FAD FADH 2     NAD + NADH + H + Electron Transport System PDH not part of TCA cycle but important for supply of acetyl CoA

22 Energy Production and Intermediates for Biosynthesis Energy Source for Certain Tissues During Starvation Energy Storage as Triacylglycerols; Cholesterol & Steroid Hormones Sources and Fate of Acetyl coA

Learning Outcomes  Describe the glycolytic pathway.  Explain the energy-requiring and energy-producing steps in the glycolytic pathway.  Explain the metabolic fate of pyruvate. 31 Jan 2012Ms.Rohini FoM 23

31 Jan 2012Ms.Rohini FoM Nov 2011Rohini K FoM 24 Thank You