Kreb Cycle

Glycolysis

`Glycolysis is the first stage which is a 10 вЂ" reaction biochemical pathway that produces ATP by substrate вЂ" level phosphorylation. Glycolysis occurs in the cytoplasm and converts into a 3 carbon molecule of pryruvate. Glycolysis begins with a 6 - carbon of glucose. Two energy phosphates from ATP molecules are added to the 6 вЂ" carbon molecule of glucose which produces a 6 вЂ" carbon molecule with two phosphates. Then the 6 вЂ" carbon molecule is split in half with 3 on each side with 1 phosphate attached.

In the second half of glycolysis, an additional inorganic phosphate is added into the 3 вЂ" carbon phosphate. The additional phosphate and the NAD+ come together and make NADH. Then it goes into a transfer, which is a reduction of ADP to ATP twice which comes out with a 3 вЂ" carbon pyruvate. ADP is converted to ATP through substrate level phosphorlyation. Which is 1 NADH and 2 ATP molecules. 4 ATP (2 ATP from each side) вЂ" 2 ATP (from the first step) = 2 ATP (the net yield). For glycolysis to continue NADH has to be recycled to NAD+ by either fermentation or aerobic respiration.

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Pyruvate Oxidation

Pyruvate begins where glycolysis leaves off. The extraction of additional from pyruvate takes place in the mitochondria in eukaryotes and in the plasma membrane in prokaryotes. First, pyruvate starts off its cycle with 3 carbons. One of the 3 carbons departs and becomes CO2 and the other two are in the acetyl group which is then attached to coenzyme A, this entire molecule is called acetyl вЂ" CoA. Pyruvate is oxidized to produce a two- carbon compound and CO2, with an electron transfer to NADH. Then the 2-carbon compound is oxidized to CO2 by the reactions of the Kreb cycle. What comes out of the pyruvate oxidation is the acetyl coenzyme A which is fed into the Kreb cycle.

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Kreb Cycle

This is the third stage, the acetyl group is oxidized here