Question

Given your answer for how many protons are pumped by NADH and knowing that 1 ATP requires 4 H+, how many ATP equivalents of energy can be provided by NADH? Note that I said "equivalents" which means you can have a fraction of ATP here. Round to 1 decimal place.Now make the same calculation for FADH2. Again, make the same assumptions.

Answer 1

Oxidative phosphorylation starts with the arrival of 3 NADH molecules and 1 FADH₂ molecule from the CAC (citric acid cycle), which shuttle high energy molecules to the ETC (electron transport chain). NADH pumps its electron to Complex I, which is at a higher energy level than the other complexes. The process of oxidation of NADH leads to the pumping of protons (H⁺) through protein complex-1 from the matrix to the inter-membrane space. The electrons that were received by protein complex-1 are given to another membrane-bound electron carrier called ubiquinone or Q. UQH₂ transports the electrons to protein complex-3 through the non-polar region of the phospholipid bilayer, UQH₂ also carries protons. When UQH₂ delivers electrons to protein complex 3, it also donates its protons to be pumped. When complex-I transfer the electron to complex-III, energy is given off to pump protons across the membrane, creating a gradient. The electron moves again to complex-IV and again pumps more electrons across the membrane. Because NADH started with complex-I, it had more chances to pumps more protons across the gradient. So complex-I pump out 4H⁺, complex-III pumps out 4H⁺, and complex-IV pumps out 2H⁺. Therefore, NADH results in 10H⁺ being pumped out. NADH results in 10H⁺ being pumped out, but FADH2 results in 6H⁺ being pumped out since it bypasses complex-I. ATP synthase makes 1 ATP for every 4H⁺ that pass through it, thus, the 10H⁺ coming from the energy of one NADH would lead to the creation of 10/4 or 2.5 ATP (3 ATPs). NADH produces 3 ATP during the ETC (Electron Transport Chain) with oxidative phosphorylation because NADH gives up its electron to complex-I, which is at a higher energy level than the other Complexes. FADH2 produces 2 ATP during the ETC because it gives up its electron to complex-II, bypassing complex-I.