GLYCOLYSIS It is known as embden- meyehof pathway (EMP) Glycolysis is sequence of reaction converting Glucose 2 Pyruvate Free energy released in this process and stored as 2 molecules of ATP, and 2 molecules of NADH Glycolysis is a universal pathway; in both prokaryote and eukaryotes In eukaryotes it occurs in Cytosol C6H12O6+ 2NAD+ +2ADP + 2 Pi 2 (CH3(C=O)COOH + 2 ATP + 2 NADH + 2 H+ +H2O

Historical Perspective: Glycolysis was the very first biochemistry or oldest biochemistry studied. It is the first metabolic pathway discovered. Louis Pasture : Fermentation is caused by microorganism. Pastuer’s effect: Aerobic growth requires less glucose than anaerobic condition. Buchner; 1897: Reactions of glycolysis can be carried out in cell-free yeast extract. Harden and Young 1905: 1: inorganic phosphate is required for fermentation. 2: yeast extract could be separated in small molecular weight essential coenzymes or what they called Co-zymase and bigger molecules called enzymes or zymase. 1940: with the efforts of many workers, complete pathways for glycolysis was established.

GLUCOSE 2 PYRUVATE 2 ACETYL CO-A 4CO2+4H2O 2 ETHANOL +2H20 2 LACTATE O2 Citric acid cycle O2 CO2 Aerobic condition Anaerobic condition 10 reactions

Two Phase of Glycolysis Preparatory Phase This phase is also called Glucose activation phase. In the preparatory phase of glycolysis, two molecules of ATP are invested. The glucose is phosphorylated,converted to fructose which again phosphorylated and cleaved into Glyceraldehyde-3-phosphate. Payoff Phase This phase is also called Energy extraction phase. During this phase, conversion of glyceraldehyde-3-phophate to pyruvate and the coupled formation of ATP take place. Because Glucose is split to yield two molecules of D- Glyceraldehyde-3-phosphate, each step in the payoff phase occurs twice per molecule of glucose.

 Glucose is phosphorylated to form glucose-6-phosphate.The reaction is catalysed by enzyme hexokinase or glucokinase.  The enzyme splits the ATP into ADP, and the Pi is added onto the glucose.  Hexokinase, requires Mg2+ for its activity. Step 1 : Uptake and Phosphorylation of Glucose Preparatory Phase

Step 2 : Isomerization of Glucose-6-Phsphate to Fructose-6- Phosphate  Glucose-6-phosphate is isomerised to fructose-6-phosphate by phosphohexose isomerase.  This reaction involves an aldose-ketose isomerisastion catalysed by phosphohexose isomerase.

 Fructose 6 phosphate is phosphorlyated to fructose 1,6 bisphosphate. Catalysed by phosphofructokinase enzyme.  It transfer phosphate group from ATP to fructose 1,6 bisphosphate. Step 3 : Phosphorylation of F-6-P to Fructose 1,6-Biphosphate

Step 4 : Cleavage of Fructose 1,6-Biphosphate  Bisphosphate aldolase catalyzes the reaction to convert fructose-1,6- bisphosphate into two three-carbon molecules: 1)Glyceraldehyde-3-phosphate 2)Dihydroxyacetone phosphate (DHAP).

Step 5 : Interconversion of the Triose Phosphates  Triose phosphate isomerase catalyzes the conversion of DHAP to glyceraldehyde-3-phosphate.  This is a reversible reaction but DHAP is eventually depleted because glyceraldehyde-3-phosphate continues in the next phase of glycolysis.

Payoff Phase Step 6 : Oxidative phosphorylation of GAP to 1,3- Bisphosphoglycerate  Conversion of glyceraldehyde-3-phosphate into 1,3- bisphosphoglycerate(1,3-BPG)  The reaction catalysed by glyceraldehyde-3-phospahte dehydrogenase  The oxidation od aldehyde to an acid is coupled to reduction of NAD+ to NADH/H+

Step 7 : Conversion of 1,3-Biphosphoglycerate to 3- Phosphoglycerate  Conversion of 1,3-bisphosphoglycerate to 3- phosphoglycerate catalysed by phosphoglycerate kinase  This is first step to produce ATP

The phosphate shifts from C3 to C2 to form2- phosphoglycerate catalysed by enzyme phosphoglycerate mutase Step 8 : Conversion of 3-Phosphoglycerate to 2-Phosphoglycerate

Enolase converts 2-phosphoglycerate to phosphoenolpyruvate (PEP), simultaneously releasing a molecule of water and creates high energy enol phosphate linkage Step 9 : Dehydration of 2-Phosphoglycerate to Phosphoenolpyruvate

 Phosphenol pyruvate converted to pyruvate producing one ATP molecule catalysed by pyruvate kinase enzyme. It is irreversible step Step 10 : Conversion of Phosphoenol Pyruvate to Pyruvate

ENZYMES Hexokinase Phosphogluco-isomerase Phosphofructo-kinase Aldolase Triosephosphate-isomerase Glyceraldehyde-3-phosphate dehydrogenase Phosphoglycerate-kinase phosphoglycerate mutase Enolase Pyruvate kinase

Energy Yield in Aerobic Glycolysis StepEnzymeSourceNo. of ATP 1Hexokinase– 3Phosphofructokinase– 6 Glyceraldehyde-3- phosphate dehydrogenase NADH(+3) x 2 = +6 7Phosphoglycerate kinaseATP(+1) x 2 = +2 10Pyruvate kinaseATP(+1) x 2 = +2 Net Yield8 ATPs

Significance of the Glycolysis Pathway Glycolysis is the only pathway that is taking place in all the cells of the body. Glycolysis is the only source of energy in erythrocytes. In strenuous exercise, when muscle tissue lacks enough oxygen, anaerobic glycolysis forms the major source of energy for muscles. The glycolytic pathway provides carbon skeletons for synthesis of non-essential amino acids as well as glycerol part of fat. Most of the reactions of the glycolytic pathway are reversible, which are also used for gluconeogenesis