Citric acid cycle

For cells to perform any function, any work, they must have energy.

You can’t go jogging or lifting weights if you’re tired, because a cell won’t work without the help of chemical energy.

The main energy currency in the cells is adenosine triphosphate, or ATP, but any nucleoside triphosphate, like guanosine triphosphate, GTP, will do.

For cells to make ATP, a process generating electricity has to take place in our mitochondria.

Electricity is power!

And thanks to this electricity, ATP is made.

Now to create electricity, electron rich molecules must deliver electrons to a chain of complexes, the electron transport chain, which move them to a final acceptor, a molecule of oxygen.

And there are two electron donor molecules: nicotinamide adenine dinucleotide, or NADH, and flavin adenine dinucleotide, or FADH2.

But of course, the cell has to produce NADH and FADH2 in the first place, and they’re produced by critical enzymes called dehydrogenases.

Dehydrogenases are the main enzymes found in the citric acid cycle or Kreb’s cycle.

In fact, the citric acid cycle is a set of 8 enzymatic reactions that start with a molecule called acetyl-CoA, and four of the enzymes, half of them, are dehydrogenases.

And in this process, AcetylCoA gets converted into carbon dioxide.

Acetyl-CoA comes from various sources depending on whether you’ve just eaten or are starving.

Let’s say that you’re hungry and a bit angry - so you’re feeling hangry.

That’s when stress hormones like glucagon, epinephrine, and cortisol start to rise.

In this hangry state, fatty acids from triglycerides become the primary source of acetyl-CoA.

Now, let’s say you have a bowl of delicious French onion soup, everything changes - insulin is plentiful and you have plenty of acetyl-CoA from breaking down glucose, fructose, and galactose -with glucose playing the biggest role.

Now, alcohol is also a source of Acetyl-CoA in the liver where it’s metabolized.

In addition, proteins can also help contribute to acetyl-CoA production.

But in the case of glucose, after a meal, one glucose, a 6-carbon molecule, splits into two 3 carbon pyruvate molecules through glycolysis, which occurs in the cytoplasm of the cell.