Metabolic Energy Production Summary

C6H12O6 + 6O2 ------- 6H2O + 6CO2 + energy (36 ATP)

1. Glycolysis: (Outside mitochondria)

Glucose (6-carbon) is phosphorylated to Fructose 1,6-bisphosphate (2 ATP used up)

F 1,6 BP split to two PGAL (3-carbon each)

Two PGAL phosphorylated to two DPGA (2 NADH +2H+ produced)

Two DPGA dephosphorylated to two pyruvate molecules (3-carbon) (4 ATP produced)

Net Gain: 2 NADH + H+; 2ATP. (These two ATPs are used up transporting the electrons from NADH + H+ to the mitochondria)

2. Preparation for Citric Acid cycle: (In mitochondria)

CO2 removed from pyruvate as Acetyl-CoA formed (2 NADH + 2H+ produced per 2 pyruvate)

Net Gain: 2 NADH + H+

3. Citric Acid Cycle (CAC) (In mitochondria)

Acetyl-CoA combines with oxaloacetic acid (4-carbon) to give 6-carbon molecule. Molecule gradually rearranged and broken down. CoA is re-used. Oxaloacetic acid regenerated for re-use.

2 x 3 NADH + H+ produced (2 x 3 because two Acetyl-CoA enter cycle per glucose)

2 x 1 FADH2 produced

2 x 1GTP produced (later converted to ATP)

2 x 2 CO2 released

So, glucose completely broken down to CO2 and high energy compounds produced

Net Gain: 10 NADH + H+

2 FADH2

2 ATP (via GTP) (This is used directly in the cell)

4. Chemiosmotic ATP Synthesis: (In inner mitochondrial membrane)

NADH + H+ releases electrons (2e-) plus hydrogen ions (2H+) to electron transport chain. NAD+ goes back to earlier stages and is reused. Electrons pass across the membrane three times, carrying 2H+ across each time, and leaving them between the inner and outer mitochondrial membranes. So each NADH +H+ carries six hydrogen ions across. Electrons from FADH2 carry four hydrogen ions across. FAD is also re-used in CAC.

So, for each glucose molecule, 68 hydrogen ions are moved across the inner mitochondrial membrane. It takes 2 hydrogen ions moving through the ATP synthetase enzyme to convert ADP + Pi to ATP (34 total.)

The electron pairs must now combine with half of an O2 molecule, and two H+ to give H2O. This is the source of the water in the respiration equation.

5. Conclusion

So, 34 ATP are formed by chemisosmotic ATP synthesis. Add these to the net gain of ATP of two formed earlier to give a grand total of 36 ATPs formed from one molecule of glucose as it is broken down to six CO2 and 6H2O molecules. The ATP is then used elsewhere in the cell.