Kreb cycle and Glycolysis

TYPES OF RESPIRATION: The oxidation of organic substance in living cells resulting in the liberation of energy is called respiration. It is of two types: 

1)AEROBIC RESPIRATION: 

This is known to occur in presence of oxygen and is described as a vast series of enzymatic reaction through which the chemical energy contained in the food is converted into energy in the form of ATP. The energy contained in food is made available for work through glycolysis and Krebs's cycle. The glucose is oxidized to its component CO2 and H20 with the release of energy in the form of ATP. The overall reaction is represented as: 

C6H12O6+ 6O2--------6CO2 +6 H20 +Energy 

The first phase of glycolysis is known to occur in cytosol of the cell where the Krebs cycle is known to take place in mitochondrial matrix. 

GLYCOLYSIS: 

Glycolysis is described as series of enzymatic reaction using glucose as raw material. It is also alternately termed as Embden-Mayerhof-Parnas(EMP) after the name of three German Plant Physiologist who work on this path way. 

1)Initially the glucose molecule accept the phosphate group of ATP and is converted into Glucose 6 phosphate in presence of Enzyme Hexokinase. 

2)The glucose 6 Phosphate accept the phosphate group of ATP and is converted into Fructose1,6 diphostate which is 6 carbon containing compound in presence of enzyme Phospho fructose kinase. 

3)The fructose 1,6 diphosphate is cleaved by the enzyme aldose into 3 phosphoglyceraldehyde(PGAL) and Dihydrooxyacetonephosphate(DHA

P).  

The DHAP is converted into its isomer 3 PGAL by enzyme phosphotriose isomerose.The 3-PGAL accepts on phosphate group from inorganic phosphate and is converted into 1,3 diphosphoglyceric acid(1,3di PGA) which donates a phosphate group to ADP and is 3Phosphoglyceric acid.In this process,a molecule of ATP is generated and the enzyme involved is PHosphoglyceric acid kinase. Intramolecular transfer of the phosphate group occurs from the 3 rd carbon of PGA to 2nd carbon therby forming 2-PGA in presence of enzyme Phosphoglycero mutase. 2-PGA loses one molecule of water and is converted into Phosphoenol Pyruvic acid(PEPA) with the involvement of enzyme enolases. The PEPA donates one phosphate group to ADP and is converted into pyruvic acid.In this process one molecule of ATP is generated and the enzyme involved is pyruvate kinase. ENERGETIES OF GLYCOLYSIS: 1)No of ATP's consumed-2 ATP 2)No of ATP's generated a)1,3 diPGA----3PGA ----1 ATP b)PEPA-----Pyruvic acid----1 ATP 1X2=2 c)Oxidation of NADH2=3 ATP 3X2=6 ATP Total ATP's generated-----10 ATP KREBS CYCLE: The 2nd phase of the oxidation of food involves the Kreb's cycle or Tricarboxylic cycle(TCA).It is series of chemical reaction by which the pyruvic acid produced is completely broken down into CO2 and water with the uptake of O2 and release energy in the form of ATP. The complete pathway was worked out by Sir Hans E Kreb(1953) for which he was awarded the nobel prize in the year 1953.All the reaction of this cycle occur in the mitochondrial matrix. For the participation of pyruvic acid in the Kreb cycle ,it is initially converted into Acetyl coenzyme A by the process of oxidative decarboxylation which can be summed up as Pyruvic acid + coenzymeA +NAD------Acetyl CoA +NADH2 + CO2 The acetyl CoA reacts with Oxalo ACetic Acid and water to form Citric acid in presence of enzyme citric acid asynthese. Acetyl CoA +OAA+ H2O------Citric acid+ co enzyme The citic acid loses one molecule of water to form sis aconotic acid which react with water to form isocitric acid. CA + excess H2O-----Sis Aconitic acid+H2O-----Isocitric acid The iso citric acid is dehydrogenated by the enzyme to form oxalo succinic acid. `ICA +NAD---------Oxalo Succinic acid+ NADH2 dehydrogenase (OSA) The OSA loses one molecule of CO2 to form alpha ketoglutaric acid. OSA-----------------------alpha ketoglutoric acid + CO2 decarboxylase The alpha ketoglutaric acid undergoes oxydate decarboxylation to be converted into Succinyl CoA. alpha ketoglutaric acid+CoA +NAD-------------------------Succinyl CoA alpha ketoglutoric acid dehydrogenase The succinyl CoA loses the CoA to be converted into Succinic acid. Succinyl COA +H2O +H3PO4-------Succinic acid +Co A+GTP(Guanoshine triphosphate) sucinyl thiokinase (GTP+ADP----ATP) The succinic acid is dehydrogenated into fumaric acid which react with one molecule of water to from malic acid. SA+FAD-------------------fumaric acid +H2O-----------malic acid(MA) Dehydrogenase The MA is dehydrogenated to form OAA by the enzyme malic acid dehydrogenase. MA+NAD--------------OAA+NADH2 ENERGETICS OF KREB CYCLE: 1)In the conversion of PA to Acetyl CoA 3ATPs( 3X2=6) 2)Iso CA------OSA 3ATPs( 3X2=6) 3)alpha keto glutaric acid------succinyl COA 3ATPs( 3X2=6) 4)SA------FA 2ATPS(2X2=4) 5)MA----OAA 3ATPs( 3X2=6) 6)Succiny COa------SA 1ATP(1X2=2) TOTAL ATP'S IN KREB CYCLE=30 ATPS TOTAL ATP'S PRODUCED FROM ONE MOLECULE OF GLUCOSE=40 ATPS TOTAL NO OF ATPS CONSUMED=3 ATPS NET GAIN OF ATPS FROM ONE MOLECULE GLUCOSE=38 ATPS