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  1. Glucose is phosphorylated twice to make a 6C sugar phosphate. 2 ATPs are used to supply the P groups. This makes the glucose more reactive and so...
  2. The 6C sugar phosphate breaks down to form 2, 3-carbon sugar phosphates, called triose phosphates (TP).
  3. Hydrogen is removed from each of the 2 TP molecules. The hydrogens are passed to 2 NADs (the NADs are reduced). 2 ATPs are made directly from the conversion of each TP to pyruvic acid (written shorthand as PA or called pyruvate) as the phosphate groups are removed.
Into glycolysis: Out of glycolysis:
1 Glucose (6C) 2 Pyruvic acids (3C)
2 NAD 2 reduced NAD (2 NADH + H+)

Net Gain = 2 ATP and 2 NADH + H+

This stage occurres in the cytoplasm. The next stage occurs in the mitochondria. From here, the reaction will only proceed if oxygen is available.

The link reaction
  1. The PA molecules enter the mitochondrion.
  2. CO2 and hydrogen are removed from each PA to create 2 2-C molecules. The hydrogen is transferred to NAD
  3. The 2-C molecule is then combined with coenzyme A (CoA) to form the 2C compound, acetylCoA. (CoA is a vitamin derivative which acts as a transporter of the 'acetate' psrt left from the PA molecule)
Into link: Out of link:
2 PA and 2 CoA 2 Acetyl CoA
g 2 CO2
2 NAD 2 reduced NAD (2 NADH + H+)