Question

What is the yield of ATP when 1 molecule of phosphoenolpyruvate is completely oxidized to CO2 in a mammalian cell with plenty of O2. What is the yield from galactose?

[Assume 1.5 net ATP generated per NADH from glycolysis, 2.5 ATP generated per NADH from later steps& 1.5 ATP generated per FADH2]

Answer 1

Conversion of phosphoenolpyruvate to pyruvate generates one ATP.

Conversion of pyruvate to acetyl Co-A gives one NADH.

Complete oxidation of acetyl Co-A via TCA cycle give thee NADH, one FADH and one GTP(ATP)

So, overall 4 NADH, one FADH and two ATP.

One NADH give 2.5 ATP, so 4*2.5 = 10 ATP

One FADH give 1.5 ATP, so 1*1.5 = 1.5 ATP.

So overall 10+1.5+2 = 13.5 ATP.

So, phosphoenolpyruvate gives 13.5 ATP upon complete oxidation.

Galactose - Galactose is converted to glucose 6-phosphate and enter glycolysis. During this process, it utilizes one ATP. One ATP is utilized when Fructose 6-phosphate is converted into Fructose 1,6-bisphosphate.

Two NADH is generated when two molecules of Glyceraldehyde 3-phosphate is converted into 1,3-Bisphosphoglycerate. Two ATP are generated when two molecules of 1,3-Bisphosphoglycerate are converted to 3-Phosphoglycerate.

Conversion of phosphoenolpyruvate to pyruvate generates one ATP.

So, overall two ATP and two NADH are produced from glycolysis and two pyruvates.

Conversion of pyruvate to acetyl Co-A gives one NADH.

Complete oxidation of acetyl Co-A via TCA cycle give thee NADH, one FADH and one GTP(ATP)

So overall So, overall 8 NADH, two FADH and two ATP from two molecules of pyruvate.

So, overall 10 NADH, two NADH and four ATP from the complete oxidation of galactose.

One NADH give 2.5 ATP, so 10*2.5 = 25 ATP

One FADH give 1.5 ATP, so 2*1.5 = 3 ATP.

So overall 25+3+4 = 32 ATP.

So overall 32 ATP are generated from complete oxidation of galactose.