CITRIC ACID CYCLE / KREB CYCLE:DEFINITION:Regarding the reaction of living body, which providesenergy for acetic acid or acetyl equivalent ozone-based phosphate bonds (suchas ATP) for storage – it is also called the citric acid cycle, tricarboxylicacid cycle.PRINCIPLE:The citric acid cycle also known as the tricarboxylicacid cycle (TCA cycle), the Krebs cycle, or it is a series of enzyme catalyzedchemical reactions, which has central importance in all living cells that useoxygen. In eukaryotic cells, matrix of the mitochondria contain the citric acidcycle present in then.
In aerobic organisms,a metabolic pathway involved theconversion of carbohydrates, fats and proteins into carbon dioxide and water sothat it generate a form of usable energy. NET EQUATION: The citric acid cycle is also called cellularrespiration, the process where your body gets energy from the food you eat. Thecitric acid cycle has the same citric acid that is found in oranges and other citrusfruits.1) Glycolysis,where the simple sugar such as glucose is broken down, also present in thecytosol.
2) Inmitochondria the pyruvate that is formed as a product is transformed intoacetyl CoA .3) AcetylCoA is modified in the mitochondria to generate energy precursors inpreparation for the next step.4) In the process ofoxidative phosphorylation, the electron are transformed to citric acid cycleand phosphorylation of ADP, and ATP is formed. This process is also occur themitochondria.How does it happen?The carbon made atom and molecules are enter andcirculate through the citric acid cycle For understanding the working of citricacid cycle first need to determine how the carbon atoms are rearranged throughthe cycle. Molecules that are electron shuttles, gain the energy that isreleased by stepwise rearrangement and subtraction of carbon in the form ofelectron that is accept by molecule are called electron shuttles. Electronshuttles like NAD+ and FADH small organic molecule, that transport highenergy electrons to the point where they need to be by gaining electronsthrough reduction and through oxidation losing electrons. The electrons thatare transported by electron shuttles are later to be used to generate ATP.
Energy shuttles: NADH: An energy shuttle which is deliver high energy electron to the electrontransport chain and eventually produce the 2-3 ATP as a end product when the energyshuttle don’t have the high energy electron it is going to oxidized or losingelectron and finally have the positive charge is called NAD+FADH2: It carries high energy electron to the electron transport chain finallythey have power of production 1-2 ATP. The FAD is the oxidized form of FADH2.High energy molecules:ATP: It is main type of energy that is used by the celland is generate by phosphorylation of ADP.GTP: GTP is similar to ATP, which can be easily convertedto ATP in the cell.Citric acid cycle-REACTIONS:There are many reactions which are involved in Kreb cycle or Citric acidcycle: REACTION 1:Formationof Citrate:-In the first reaction of citric acid cycle theoxaloacetate react with acetyle-CoA to form citric acid.The first reaction is catalyzed bycitrate synthase enzyme. Once the two molecules are joined the water moleculeattack at acetyl group main release the coenzyme A from this complex.
Citratesynthase:(enzyme)The enzyme citrate synthase is present in nearly allliving cells and act as a pace-making enzyme in the citric acid cycle’s firststep. Citrate synthase is present in eukaryotes but is is made up of nuclearDNA instead of mitochondrial. It is synthesized from cytoplasmic ribosomes,then transported into the mitochondrial matrix. Citrate synthase is commonlypresent as a quantitative enzyme marker for the presence of intactmitochondria.
.Oxaloacetate is regenerated after the completion of one krebcycle.REACTION 2: Formation of Isocitrate:The next reaction of the Kreb cycle is catalysed by acontinaseenzyme. In this reaction overall two H2O molecules are produced onewater molecule is removed and other water molecule is put back into anotherlocation. The overall effect of this reaction is that the shifting of -OH groupfrom position 3 to the position 4.
The yield that get is isocitrate molecule. Acontinase:(enzyme)Aconitase(aconitate hydratase) is an enzyme that catalyzes the stereo-specific isomerizationof citrate to isocitrate via cis-aconitate in the tricarboxylic acid cycle, anon-redox-active process. REACTION 3:Oxidationof Isocitrate to ?-Ketoglutarate:Two events occur in citric acid cycle’s thirdreaction.
In the first reaction the formation of NADH from NAD. The enzyme thatcatalyzed this reaction is isocitrate dehydrogenase enzyme.This catalyze theoxidation of -OH group at 4 position of isocitrate and yield is intermediatefuther in the second event carbon-dioxide is removed and yield isalpha-ketoglutarate. Isocitratedehydrogenase: (IDH),is an enzyme that have role in the citric acid cycle to catalyzes the thirdstep of the cycle: the oxidative decarboxylation of isocitrate, producingalpha-ketoglutarate (a-ketoglutarate) and CO2 while converting NAD+ to NADH. REACTION 4: Oxidationof ?-Ketoglutarate to Succinyl-CoA:In this reaction the CO2 is removed fromthe alpha ketoglutarate and another molecule that is coenzyme A is added atthis place. The decarboxylation is happened due to reduction of NAD into NADH. Theenzyme that catalyse this reaction is alpha-ketoglutarate dehydrogenase.
Theconversion mechanism is same as in the previous steps pyruvate metabolism. Theresulting molecule that generate is succinyl-CoA.