Question

How many ATP molecules will be produced in a brain cell (neuron) from a glucose molecule involving electron transport chain only?
A. 32
B. 16
C. 38
D. 34

Answer 1

Hint: Glucose gets converted into 2 pyruvate molecules after the glycolysis. TCA cycle gives NADH and FADH2 + ATP. One NADH = 2.5 ATP and 1 FADH2 = 1.5 ATP. Glycolysis is followed by TCA cycle ( Kreb cycle) and then comes the electron chain transport.

Complete answer:
Let us understand this whole process in detail.
1. GLYCOLYSIS – The process of conversion of one glucose molecule into two pyruvate molecules.

In this figure, in the first half of the glycolysis ATP is being converted to ADP that is it is being utilized. Whereas in the second half, 1 NADH molecule is generated and 4 ATP molecules are being generated. As one NADH = 2.5 ATP. So now we have 2.5 + 4 = 7 ATP.

2. Oxidative decarboxylation of pyruvate – In this, one pyruvate will give one acetyl CoA.

This process will generate 2 NADH molecules, each from one pyruvate.
So we will have 2.5 x 2=5 ATP.

3. Kreb’s Cycle: Conversion of acetyl CoA to CO2, NADH, FADH2 and ATP.

In the Krebs cycle, 3 NADH, 1 FADH2 and 1 ATP is produced (from 1 acetyl CoA only)
As 1 glucose gives 2 acetyl CoA, so, at the end of this process, we will have 6 NADH(15 ATP), 2 FADH2 (3 ATP) and 2 ATP.
The sum total of all the ATP till here is 7 + 5 + 20 = 32 ATP.

After this, these ATP’s are moved to the electron chain transport.
So the answer is option A - 32

Note:
Glycolysis starts in the cytoplasm of the cell but terminates in the mitochondria. That pyruvate is generated in the mitochondria. Kreb’s cycle then takes place in the mitochondria where the next biochemical reactions take place. These processes are part of the cellular respiration.