METABOLISM PART 2: THE KREBS CYCLE AND OXIDATIVE PHOSPHORYLATION

In the metabolism part 1 post, I discussed why the body can use any of the three dietary macronutrients we eat to produce energy. Any macronutrient can lead to energy because they are all ultimately broken down into Acetyl-CoA and fed into something called the Krebs cycle. The Krebs cycle then uses Acetyl-CoA to produce ATP.

The Krebs cycle

The Krebs cycle is a collection of 8 reactions that produce ATP and other energetic compounds for energy production. The Krebs cycle takes place in Mitochondria, the metabolic energy factory of our cells. The energetic compounds generated in the Krebs cycle can undergo oxidative phosphorylation which creates more ATP. Oxidative phosphorylation isn’t anywhere near as complicated as it first sounds if we can break it down. Remember OILRIG – oxidation is loss and reduction is gain. Oxidation means that something will lose electrons and hydrogens, reduction is the opposite. Phosphorylation means we add phosphate. So oxidative phosphorylation means we take electrons and hydrogen and use their energy to add phosphate to something. That something is adenosine diphosphate (ADP) which means adenosine with two phosphates. Guess what we get when we add another phosphate (P) to ADP? That’s right, adenosine triphosphate (ATP) – our cellular energy store.

Oxidative phosphorylation

The way that electrons and hydrogen are used to do this is pretty complicated; it uses something called a hydrogen pump, ATP synthase, and an electron transport chain. What happens is the electron transport chain is a hydrogen pump that passes electrons between them. When they do this, they use the electron energy to pump the hydrogens we got from oxidising the stuff from the Krebs cycle, out of the mitochondrial matrix. Those hydrogens then flow back in through ATP synthase, which causes it to turn and turn ADP into ATP. I like to think of this in simple terms. It’s like burning our food (oxidising) to collect water (the hydrogens), then pouring that water through a windmill to spin it (ATP synthase), turning the windmill makes energy (ATP) kind of like a generator!

The takeaway– We get energy from proteins passing around electrons. Crazy. I know.

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