Question

1- Describe two ways to produce glucose from fatty acids ?

2- Under aerobic conditions, the number of ATPs produced from 1 molecule of glucose going through glycolysis and citric acid cycle is ?

Answer 1

1. Pyruvate is a common precursor for the formation of glucose and hence the pathway for gluconeogenesis remains the same for producing glucose from pyruvate. Now note that fatty acids can give rise to either (a) Acetyl CoA or (b) pyruvate. Acetyl CoA will then convert to pyruvate and start glyconeogenesis. So the two intermediates (a) and (b) for the two ways in which one can produce glucose from fatty acids.

2. In glycolysis, one molecule of glucose would give 2 molecules of ATP and 2 Molecules of NADH. Now these two NADH, when in Electron Transport Chain can give rise to a total of 4 ATP. So in glycolysis, we can get 6 ATP molecules. But it is better to say we produce only 2 molecules of ATP from one glucose in glycolysis.

In Citic Acid cycle we get, Six NADH + H+ molecules, two FADH2 molecules, four CO2 molecules, and two ATP molecules.

(here I have not converted the equivalence of FADH2 and NADH, they can be converted to 3 and 2 ATP respectively using Electron transport chain, that would give a net gain of 36 ATP from one molecule of glucose in the entire breakdown process )

ETC will give 32 ATP, Substrate level phosphorylation will give 2 ATP from the citric acid cycle, and glycolysis will give 2 ATP. (net gain = 36 ATP molecules per glucose)