Question

One molecule of glyceraldehyde-3-phosphate is fed into glycolysis. Which and how many electron carrier molecule(s) are made during (A) the glycolytic breakdown of this molecule, during (B) acetyl-CoA production and during (C) the citric acid cycle? (D) How many H⁺ are translocated across the mitochrondrial membrane due to the re-oxidation of these electron carriers? Write the numbers into the respective boxes.

This question is very important for me to understand. Please only respond if you are answering all parts and are confident they are correct. Thank you!

Answer 1

a) glyceraldehyde-3-phosphate is converted to 1,3-bisphosphoglycerate by glyceraldehyde-3-phosphate dehydrogenase, during this reaction one NADH is produced, this is the only step in glycolysis, which produces a reduced electron carrier, so from a glyceraldehyde-3-phosphate molecule one reduced electron carrier is produced via glycolysis.

then it is converted to pyruvate via series of reactions and 2 ATPs are produced.

b) from a glyceraldehyde-3-phosphate molecule one pyruvate is produced, it is converted to one acetyl CoA, by pyruvate dehydrogenase, during this reaction one NAD+ is reduced to NADH, NADH is a reduced electron carrier, so during acetyl-CoA production, one reduced electron carrier is produced.

c) during the citric acid cycle with one acetyl CoA 3 NADH, 1 FADH2 and one ATP are produced. FADH2 and NADH are reduced electron carriers.

so number of electron carriers produced by TCA cycle = 4

d) when one NADH is oxidized via the electron transport chain 10 H+ are pumped into the intermembrane space from the matrix, here total number of NADH=5 so using 5 NADH, 5*10=50 H+ are pumped into intermembrane space.

when one FADH2 is oxidised via the electron transport chain 6 H+ are pumped into the intermembrane space from the matrix, here total number of FADH2=1 so using 5 NADH, 1*6=6 H+ are pumped into intermembrane space.

( NADH is oxidised by complex I and reduces the coenzyme Q, Coenzyme Q is then oxidised by complex III and reduces the cytochrome c, cytochrome c is then oxidized by complex IV and reduces oxygen to water.

complex I pumps 4 H+. complex III pumps 4 H+, complex IV pumps 2 H+ to the intermembrane space, so a total of 10 H+ are pumped into intermembrane space when an NADH is oxidised.

FADH2 is oxidised by complex II and reduces the coenzyme Q, Coenzyme Q is then oxidised by complex III and reduces the cytochrome c, cytochrome c is then oxidised by complex IV and reduces oxygen to water.

complex II does not pump any H+ into the intermembrane space, complex III pumps 4 H+, complex IV pumps 2 H+ to the intermembrane space, so a total of 6 H+ are pumped into intermembrane space when an FADH2 is oxidised.