Question

Which best explains why fatty acids produce more energy per carbon than glucose?

a. Glucose must proceed through more pathways to yield ATP

b. Fatty acids are already located in the mitochondrial matrix

c. Glucose molecules are already partially oxidized

d. All of the above

Answer 1

Time right answer is D) all of the above

1) Primarily, both fatty acid and glucose breakdown to form acetyl CoA and ATP. Fatty acid produce 3 Acetyl CoA with ATP while glucose forms 2 Acetyl CoA molecule with ATP.

When calculations are done till this step, ATP produced per 6 carbon: it is 11.5 in glucose vs 9.5-10.5 in fatty acid.

My point is that even though more ATP is produced in glucose till this step, yet fats produce more energy, it is because of less acetyl CoA production in glucose vs fats which is used in Krebs cycle to complete the respiration and produce more ATP in the next and final part of respiration.

So because of extra decarboxylation reaction in glycolysis of glucose molecule ( which is not found in beta oxidation of fatty acids) less Acetyl CoA is formed and hence less energy is produced per carbon.

2) secondarily, the beta oxidation takes place in Mitochondria itself. So no energy is lost in transporting the Acetyl CoA inside the Mitochondria via shuttle. But the glycolysis of glucose occurs in cytoplasm, so energy is lost in shuttle system to transport Acetyl CoA into the Mitochondria for krebs cycle and hence less energy is produced

3) the formula of glucose is (CH2O) and that of fatty acid is (CH2)n. Here as we can see the glucose is already partially oxidised. So it's clear that more hydrolysis reaction occurs to hydrolyse fatty acid and hence more exothermic reaction occurs and hence more energy is released in fats oxidation.