Tuesday, 4 August 2020

Krebs (TCA) Cycle and it's Products

Krebs cycle also known as tricarboxylic acid cycle, it is a biochemical pathway that is used to generate energy to the oxidation of acetyl-coA. It is also used for the synthesis of NADH and for the production of the amino acid. Krebs cycle takes place in mitochondria of the eukaryotes and cytosol of the prokaryotes.


The first steps involved is actually a preparatory step which begins with pyruvate. Pyruvate is derived through the glycolysis of glucose which is 6 carbon compound. The next step includes the oxidation of pyruvate into acetyl-coA by the enzyme pyruvate dehydrogenase complex and in this reaction a molecule of carbon dioxide and a molecule of NADH is generated. The acetyl-coA is a 2 carbon compound, in the next step the acetyl-coA combines with oxygen as it eight.which is a four carbon compound to form citrate and hence the resulting molecule is six carbon compound this reaction is catalyzed by the enzyme citratesynthase. In the next step the citrate is isomerized in to isocitrate by the enzyme aconitase.

Next the isocitrate is oxidized into alpha-ketoglutarate by the enzyme isocitrate dehydrogenase and in this reaction a molecule of NAD is reduced to NADH and one molecule of carbon dioxide is generated. Hence the alpha-ketoglutarate is a 5 carbon compound since one molecule of carbon is lost into carbon dioxide. Next the alpha-ketoglutarate is converted into succinyle-coA by the enzyme alpha ketoglutarate dehydrogenase and in this reaction also a molecule of NAD is reduced to NADH and a molecule of carbon dioxide is released, hence the succinyl-coA is four carbon compound. In the next step this succinyl-coA is converted into succinate by the enzyme succinyl-coA synthase, in this reaction a molecule of GTP is generated. Next succinate is converted into fumarate by the enzyme succinate dehydrogenase in this reaction a molecule of QH2 is generated which is used for the production of FADH2. Fumarate is then converted into malate by the enzyme fumese. In the last step the malate is converted into oxaloacetate by the enzyme malate dehydrogenase, in this reaction also NAD is reduced to NADH.

Let's look at the result of the kreb's cycle through each cycle of the Krebs cycle following products are generated
3 molecular of NADH, 1 molecule of FADH2, 1molecule of GTP and 2 molecule of carbon dioxide. Now since glucose is split into two pyruvate compounds, for each molecule of glucose this cycle runs twice, hence the products formed are 6 NADH, 2 FADH2, 2 GTP and 4 CO2.
All the NADH and FADH2 are next fed to the electron transport chain for the generation of ATP.

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