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Electron Transport Chain ‘Story”

The electron transport chain is composed of four protein complexes which are embedded in the inner membrane of the mitochondrion along with two mobile carriers (mobile carrier Q {coenzyme Q} and mobile carrier C {cytochrome C} that shuttle electrons through the ETC. The ETC is where the greatest amount of ATP is synthesized. Note: Cytochromes are proteins that have a heme bonded to them.

Electron Transport Chain Story
NADH+H+ arrives from Stage II of carbohydrate metabolism or Stage III (TCA cycle) to the ETC and immediately oxidizes to NAD+ with its protons (hydrogen ions) going into the matrix and its electrons (e-) going to cytochrome complex I. As the electrons arrive on complex I the complex immediately goes through redox (reduction and oxidation). This reaction creates a proton pump within complex I, pumping (or translocating) 4 protons from the matrix through the protein into the intermembrane space. The electrons now transfer to mobile carrier Q and NAD+ returns to its original source to pick up more hydrogens.

FADH2 arrives from the TCA cycle to the ETC and goes directly to cytochrome complex II. FADH2 oxidizes to FAD with its protons going into the matrix and its electrons going to complex II. FAD returns to the TCA to pick up more hydrogens. Cytochrome complex II goes through redox but it does NOT create a proton pump. Mobile carrier Q picks up all of the electrons on complex II and shuttles the electrons to complex III. The electrons are transferred to complex III and it immediately goes through redox (reduction and oxidation). This creates a proton pump, pumping 2 protons from the matrix through complex III directly into the intermembrane space of the mitochondrion. (NOTE: there are many mobile carrier Q enzymes present in the ETC).

The electrons are now shuttled to complex IV by mobile carrier C. As the electrons transfer onto cytochrome complex IV it immediately goes through redox. This creates a proton pump, pumping 4 protons from the matrix through cytochrome complex IV directly into the intermembrane space of the mitochondrion.

The electrons have no place to go from complex IV. So, an oxygen atom, which has a very strong attraction for electrons, picks up a couple electrons (from complex IV) and two protons from the matrix to form water. In essence, the FINAL acceptor of the electrons at complex IV is oxygen (which forms water with the protons and electrons it accepts into its structure). This is actually 20% of the water our bodies produce and use (the rest we must intake from our fluids and foods qwe intake) and it is referred to as ‘metabolic water.’ (because it is made in metabolism)

The many protons in the intermembrane space have created a hydrogen ion concentration (charge) that the cell does not like. All cells prefer homeostasis. Therefore, ATP synthase (a special protein embedded in the inner membrane that is NOT part of the ETC) pumps several protons back into the matrix. As the protons go into the matrix energy is liberated to phosphorylate ADP with Pi, thus synthesizing ATP. The ATP will leave the mitochondrion and go where energy is needed in the cells (for life processes).

End

Class, CLICK HERE to see a fabulous graphic of the ETC.

Click here for a YOUTUBE video explaining ATP Synthase