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7.2.2.2.4. Energy balance of cellular respiration

Energy balance of cellular respiration

The glycolysis occurs in the cytosoltwo molecules of ATP directly and two molecules of NADH. If oxygen is available, the electrons from NADH enter the electron transport chain of the inner mitochondrial membrane, producing three ATP molecules for every NADH. Therefore, the yield of glycolysis is (6 + 2) 8 ATP .  

In some cells, carrying electrons from NADH  from glycolysis, the cytosol to the mitochondrial inner membrane lowers the net yield of these two NADH only four ATP instead of 6 ATP, so the performance of glycolysis it will be 6 ATP (adding the two ATP molecules obtained directly).

Then, the passage from pyruvic acid to acetyl-CoA, in the mitochondrial matrix, produces two molecules of NADH for each molecule of glucose, whose electrons in the respiratory chain will produce 6 ATP.  

In the Krebs cycle, two molecules of acetyl-CoA are introduced and two of GTP (equal to 2 ATP), six molecules of NADH and two of FADH2 are obtained.

In the electron transport chain , the six molecules of NADH and the two of FADH 2 produce 22 ATP, so in the Krebs cycle, for each molecule of glucose, 24 ATP is obtained.

The total yield produced by the complete oxidation of glucose is 36 or 38 ATP molecules, of which only two originate in the cytosol, outside the mitochondria.

Global reaction of cellular respiration:

Glucose + 6 O 2 + 38 ADP + 38 Pi → 6 CO 2 + 6 H 2 O + 38 ATP

Questions that have come out in University entrance exams (Selectividad, EBAU, EvAU)

Aragon.  September 2009, option B. 4. (2 points).

In relation to the energy metabolism of cells, answer the following questions:

a) In what metabolic process is the most ATP obtained ?

b) What other routes supply ATP?

c) What is the incidence of the presence or absence of Oxygen?

d) What role do membranes play in ATP synthesis in mitochondria and chloroplasts ?

Murcia, July 2020, question 2.3

23. Regarding aerobic respiration of glucose:

a) Indicate each of its stages and where they occur in the cell (0.5 points)
b) Describe each of these stages, indicating the initial substrates and the final products of each one. (0.5 points)
c) Complete the description above adding the oxidation / reduction and energy balance. (0.5 points)