Urea cycle; oxidative phosphorylation 2

Published on April 19, 2020 Reviewed on November 27, 2022   49 min

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Greetings. My name is Jerry Feigenson. I am a professor at Cornell University in the USA. Welcome to Part 2 of lecture 18. We ended Part 1 with a brief discussion of Peter Mitchell's breakthrough chemiosmotic theory that energy is stored as a gradient of protons and voltage across the inner mitochondrial membrane.
In this Part 2, you will see four different protein complexes that make up the mitochondrial electron transport chain. And finally, we will look at the ATP synthase enzyme, which uses this gradient to catalyze ATP synthesis.
We're going to look at reactions that happen in liver mitochondria and especially with the inner membrane of the mitochondria. So let me orient you. The outer membrane of mitochondria is very permeable. We'll show this as dashed lines schematically indicating lots of holes in the outer mitochondrial membrane. Then there's an inner mitochondrial membrane which is extremely tight, extremely impermeable. It's the tightest of all known biological membranes. Then we'll notice that the cytosol has a higher proton concentration and a more positive electrical potential than the matrix. What about the enzymes that are involved? Well, early on it was realized that there are four protein complexes that are involved in ATP synthesis. They are indicated as complex 1, complex 2, complex 3, and complex 4, and we're going to look at reactions in each one of these. Now it's realized that complexes 1, 3, and 4 seem to be loosely bound together into what could be called a super complex. Actually, each complex by itself can work to generate the proton and voltage gradient. But now, complexes 1, 3, and 4 are known to be associated and there's further research going on to understand the importance of that finding. It's these four complexes that get and give electrons by means of mobile electron carriers. So let's see how that works.