Question

What is the ATP net output for aerobic respiration for the following steps:

Glycolysis

Kreb Cycle

Electron Transport Chain

State how many of the following will be produced during glycolysis with two glucose molecules:

Pyruvate

ATP    

NADH

Answer 1

Glycolysis, Kreb's cycle and Electron transport Chain are all forms of cellular respiration.

Aerobic glycolysis is the process by which one mole of glucose is oxidised to two moles of pyruvate. 2 ATP molecules are formed from the conversion of 1,3 Biphosphoglycerate to 3 phosphoglycerate and the other two molecules of ATP are formed from the conversion of phosphoenolpyruvate to pyruvate. Wheras, in the preparatory phase, the conversion of glucose to glucose 6 phosphate requires one ATP and the conversion of fructose 6 phosphate to fructose 1,6 bsphosphate requires another ATP.

Hence,the overall balance is: ( 4ATP-2ATP) = 2 ATP molecules.

Kreb cycle is the process where modification of acetyl CoA takes place in mitochondria to produce ATP molecules for electron transport chain. Kreb cycle essentially produces 2 molecules of ATP for every molecule of glucose, 10 carrier molecules and CO₂ molecule. The 10 carrier molecules are carried forward in the electron transport chain.

Electron Transport Chain is the process whereby electrons derived from the intermediates of the Kreb's cycle is used in the generation of ATP. At the end of the electron transport chain, 32 molecules of ATP are produced.

So, in total 36 molecules of ATP are produced as a result of oxidative phosphorylation.

Process	Yield of ATP
Glycolysis 2(1,3 biphosphoglycerate 3 phosphoglycerate) 2( phosphoenolpyruvatepyruvate)	2 molecules 2 molecules
Kreb's cycle 2 molecules of ATP formed from 2 molecules of succinyl CoA	2 molecules
Electron Transport Chain 2NADH formed in glycolysis, each yiels 2ATP. 2NADH formed in the link reaction, each yields 3ATP. 2FADH2 formed in the TCA cycle, each yields 2 ATP 6NADH formed in the TCA cycle, each yields 3 ATP.	4 6 4 18

So, total yield of ATP is 36 molecules.