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OXIDATIVE PHOSPHORYLATION SIMPLIFIED

Updated: Nov 8, 2023

OXIDATIVE PHOSPHORYLATION SIMPLIFIED


source: ZMEScience

Some of my students struggle with cellular respiration so I decided to write the most simplified explanation for cellular respiration. This particular post covers the 3rd and final part of cellular respiration called, "Oxidative Phosphorylation," which occurs THROUGH the Electron Transport Chain (ETC) as shown above.

  • What is Cellular Respiration? process where macromolecules are used to produce ATP in the presence of oxygen

  • What is ATP? short for Adenosine Triphosphate, which is the primary energy used by cell

  • So why is cellular respiration necessary? it produces energy for our cells so they can survive

  • What is Oxidative Phorphorylation? process by which NADH and FADH2 (high-energy electron carriers) are converted to ATP


Oxidative Phosphorylation (Location: mitochondrial inner membrane)

ETC is a set of protein complexes and electron carriers within the mitochondrial inner membrane. They collaboratively pump protons (H+) to the intermembrane space, which in turn builds a chemiosmotic gradient that will later activate ATP Synthase to create ATP.

source: Study.com














1st step:

NADH and FADH2 are used by the ETC to pump H+ across the inner membrane into the intermembrane space


2nd step:

Chemiosmotic gradient is established within the intermembrane space with a build-up of H+

  • chemiosmotic gradient refers to the proton concentration being higher in the intermembrane space than in the mitochondrial matrix.

source: The Sports Edu
















3rd step:

The chemiosmotic gradient allows H+ to cross ATP Synthase into the mitochondrial matrix, which in turn phosphorylates ADP to ATP


Let's Get Counting (**TEST MATERIAL**)

Krebs Cycle & Oxidative Phosphorylation in the presence of oxygen (=aerobic respiration). Glycolysis however doesn't require oxygen so it is an anaerobic process.

Glycolysis --> 2 ATP, 2 NADH
Krebs Cycle --> 2 ATP, 6 NADH, 2 FADH2

shows the total number of ATP, NADH and FADH2 after glycolysis and Krebs Cycle.


The extra 2NADH comes from Pyruvate Decarboxylation (aka "Pyruvate Oxidation" as seen in diagram below) prior to Krebs Cycle, where two pyruvates from glycolysis produce two Acetyl-CoA, from which 2NADH in total are produced.


source: https://slideplayer.com/slide/14046415/

  1. Note that the 2 NADH from glycolysis remains in the cytoplasm and needs to be brought into the mitochondria. This shuttle process replaces the 2 NADH to 2 FADH2, resulting in a total 4 ATP, 8 NADH, and 4 FADH2.

  2. Each NADH can produce up to 3 ATP and each FADH2 up to 2 ATP

  3. (8 NADH x 3 ATP = 24 ATP) + (4 FADH2 x 2 ATP = 8 ATP) = 32 ATP (from electron carriers through oxidative phosphorylation)

  4. (32 ATP + 4 ATP [created from glycolysis and Krebs Cycle]) = 36 ATP

  5. All in all, 1 glucose molecule which undergoes glycolysis, Krebs Cycle and Oxidative Phosphorylation can produce 36ATP

*Do note that efficiency of ETC may not be 100%, so each NADH may only create 2.5 ATP and each FADH2 create 1.5 ATP

source: BYJU'S

Aerobic respiration takes into account GLYCOLYSIS + KREBS CYCLE + ELECTRON TRANSPORT SYSTEM

What max ATP can aerobic respiration create? ANSWER IS 36 ATP



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