Give the schematic representation of an overall view of Krebs cycle.

Explanation

Acetyl Co - A formed from pyruvate durinf the process of respiration undergoes complete oxidation through a series of reaction which was discovered by Sir Hans Kreb's. Citric acid is the first stable compound having three carbonyl groups . Hence , Kreb's cycle is also known as tri - carboxylic acid cycle or citric acid cycle .
Formation of citric acid : Acetyl Co-A which is formed from pyruvate reacts with oxalacetate (4 C) to form citrate . One `H_(2)O` molecule is utilized in the reaction . Enzyme citrate synthetase catalyses this reaction . Co - A produced during this reaction is recycled, for the conversation of pyruvate to acetyl Co - A.
Isomerisation of citrate to isocitrate (Dehydration and hydration ) : Citrate undergoes isomerisation to form isocitrate.
The steps are :
1 . First of all citrate undergoes dehydration by loosing one molecule of `H_(2)O` and forms cis-aconitate under enzyme acotinase .
2. Cis - aconitate undergoes hydration to form isocitrate by taking back one molecule of `H_(2)O`.
` Cis - aconitate + H_(2)O overset ("Acotinase") to` Isocitrate.
Oxidaton of Isocitrate : After oxidation isocitrate forms oxalo - succinate . In this reaction H removed is accepted by coenzyme NAD which form `NADH_(2)` after accepting H , in presence of isocitrate dehydrogenase with `Mn^(2+)` as co- factor .
Isocitric acid + NAD `overset ("Isocitrate dehydrogenase") to "Oxalosuccinate + NADH_(2)"`
Decarboxylation : Oxalosuccinate undergoes decarboxylation in the presence of decarboxylase to form `prop-` ketoglutarate . A molecule of `CO_(2)` is relased .
`"Oxalosuccinate" overset("Decarboxylase")to prop - "ketoglutarate" + CO_(2) `
Oxidative decarboxylation : `prop` - ketoglutarate under- goes oxidative decarboxylation to form succinyl Co- A , in presence of `prop` - ketolutarate dyhydrogenase .
`prop - "ketoglutarate" + NAD + Co-A to "Succinyl" Co - A + NADH_(2) + CO_(2)`
Hydration and phosphorylation of succinyl Co-A:
It undergoes hydrolysis to form succinate with release of Co-A , in the presence of succinyl thiokinase. Energy released is utilised by GDP to from GTP (Guanosine triphosphate ) and iP. GTP formed reacts with ADP to form ATP . This type of ATP formation is called substrate level phosphorylation .
Oxidation of succinate : Succinate oxidises to form fumarate . `H_(2)` removed is accepted by FAD to form `FADH_(2)`. Enzyme succinate dehydrogenase is present and `Fe^(2+)` as a co - factor .
Succinate + FAD `overset("Succinate dehydrogenase ") to Fe^(2+) "Fumarate" + FADH_(2)`
Hydration of fumarate : After hydration fumarate combines with `H_(2)O` to form malate in the presence of fumarase .
` "Fumarate" + H_(2)O overset("Fumarase") to Malate.
Oxidation of Malate : Malate undergoes oxidation to form oxaloacetate. H removed during this reaction is accepted by NAD to from `NADH_(2)`.
`Oxaloacetate is thus regenerated to combine with acetyl Co - A to keep the cycle going .
Malate + NAD `overset("Malate dehydrogenase") to "Oxaloacetate + NADH_(2)"`