Question

Which steps in Kreb’s cycle involve decarboxylation? Please describe the two different types of C-C bonds cleaved to form CO2 in the cycle. How is the anion stabilized in each case?

Answer 1

Kreb`s cycle or citric acid cycle if the series of recation taking place in the aerobic organisms to release the energy. During this cysclic pathway, acetyl coenzyme A (acetyl Co-A) and oxalocaetate fisrt form citric acid, which undergo decarboxylation and converted back in to oxalic acid. During this recation two CO₂ molecules are released as byproduct, three NAD and one FAD molecules are reduced and one ATP molecule released as energy.

The perticular decarboxyylation step invloved is the first one with the conversion of isocitrate intermediate (which is formed from citric acid) to alpha-ketoglutarate with removal of one CO₂ molecule and reduction of one NAD⁺ to NADH. The recation involved is shown in below figure (Reaction 1), The intermediate ion formed during this step is stabilized by transfer of one H from C2 carbon to C3 carbon.

The other decarboxilation step involved is the successive removal of CO₂ from alpha-ketoglutarate with the addition of Co-A. In this step Co-A oxidizes alpha-ketoglutarate and reduces one NAD⁺ to NADH. The Co-A stabilized intermediate molecule of this step is called succinyl Co-A. The reaction involed in this step is shown in folloning Figure (Reaction 2). In the next steps, succinyl Co-A undergoes reaction with Phostphate and relaeses energy and also undergoes further reaction to convert back to oxalic acid.