Question

What is the ATP yield from one molecule of glucose and how ATP is generated at each process:

a. Glycolysis

b. Kreb's cycle

c. Electron Transport chain

Please specify if any ATP are removed from the total yield as a result of these ATP being required to initialise the reaction

Answer 1

A) glycolysis - it is a process undergone to produce 2 molecules of pyruvate from the one glucose molecule. there are mainly two phases in the glycolysis. preparatory and payoff phase. in the preparatory phase 2 molecules of ATP are used. in the following steps-

1. glucose -> glucose6phosphate (using hexokinase)

2. fructose6phosphate -> fructose 1,6biphosphate (using phosphofructokinase-1)

in the payoff phase a total of 4 ATP and 2 NADH is generated in the following steps:-

1. (2) glyceraldehyde3-phosphate -> (2) 1,3bisphosphoglycerate (2 NADH is produced using glyceraldehyde3-phosphate dehydrogenase)

2. (2) 1,3bisphosphoglycerate -> (2) 3phosphoglycerate (2ATP is liberatted using phosphoglycerate kinase)

3. (2)phosphoenolpyruvate -> (2) pyruvate (2ATP is produced using pyruvate kinase)

So, in total, the energy produced = 4 ATP produced + 2 NADH produced - 2 ATP utilized

= 2 ATP produced + 2 NADH produced (* 1 NADH = 2.5 ATP)

So net ATP production from glycolysis is 2ATP

The remaining 2 NADH goes to Electron transport chain

b. Krebs cycle - it is the central metaolic hub of the cell. there are total of 8 steps in the cycle. in which the energies NADH, FADH2 and GTP are produced.

step 1 - condensation reaction (2C+ 4C = 6C)

acetyl Co-A + oxaloacetate -> citrate (using citrate synthase, no any energies are produced)

step 2 - isomerization reaction

citrate -> isocitrate (using aconitase, no any energies are produced)

step 3 - 1st oxidative decarboxylation

isocitrate -> alpha ketoglutarate ( NADH and CO2 is produced , isocitrate dehydrogenase is used in the reaction)

step 4 - 2nd oxidative decarboxylation

alpha ketoglutarate -> succinyl CoA (NADH is generated , alphaketoglutarate dehydrogenase complex is used)

step 5 - substrate level phosphorylation

succinyl CoA -> succinate (ATP is generated, succinyl CoA synthetase is used)

step 6 - dehydrogenation

succinate -> fumerate (a molecule of FADH2 is produced, here the enzyme is succinate dehydrogenase)

step 7 - hydration

fumarate -> malate (using enzyme fumerase, no energy produced)

step 8 - dehydrogenase

malate -> oxaloacetate (using enzyme malate dehydrogenase, a molecule of NADH is produced)

therefore in 1 TCA cycle,

3NADH, 1 FADH2 AND 1 ATP is produced ( 1FADH2 = 1.5 ATP)

for 1 molecule of glucose it undergoes 2 TCA cycles,

hence, 6 NADH, 2 FADH2 and 2ATP is produced.

So there will net ATP of 2ATP and the remaining 6 NADH, 2 FADH2 goes to electron transport chain.

c) Electron transport chain - there are mainly four complexes within this cycle.

The NADH complex and FADH2 complex receives NADH and FADH2 respectively and give rise to H+ and electrons which is received by F1-F0 complex to form ATP.

Thus a total of 7 NADH from a molecule of glucose is converted to 8 x 2.5 ATP = 20 ATP

And the 2 FADH2 from a molecule of glucose is converted to 2 x 1.5 ATP = 3 ATP

And also in the conversion of pyruvic acid to acetyl CoA a molecule of NADH is released and as 2 molecules of pyruvic acid is produced from a molecule of glucose 2 molecules of NADH is produced.

Thus 2 more NADH is converted to ATP = 2 x 2.5 ATP = 5 ATP

Thus a tota of 28 molecule of ATP is produced from electron transport chain

Thus in altogether of 28 ATP of ETC + 2 ATP of TCA + 2 ATP of glycolysis = 32 ATP