Such molecules can enter the intermembrane space, but most of them cannot pass the impermeable inner membrane. This membrane thus resembles a sieve that is permeable to all molecules of 5000 daltons or less, including small proteins. The outer membrane contains many copies of a transport protein called porin (discussed in Chapter 11), which forms large aqueous channels through the lipid bilayer. In the liver, an estimated 67% of the total mitochondrial protein is located in the matrix, 21% is located in the inner membrane, 6% in the outer membrane, and 6% in the intermembrane space. The general organization of a mitochondrion. In others they remain fixed in one position where they provide ATP directly to a site of unusually high ATP consumption-packed between adjacent myofibrils in a cardiac muscle cell, for example, or wrapped tightly around the flagellum in a sperm ( Figure 14-6). Thus, the mitochondria in some cells form long moving filaments or chains. As they move about in the cytoplasm, they often seem to be associated with microtubules ( Figure 14-5), which can determine the unique orientation and distribution of mitochondria in different types of cells. Time-lapse microcinematography of living cells, however, shows that mitochondria are remarkably mobile and plastic organelles, constantly changing their shape ( Figure 14-4) and even fusing with one another and then separating again. Mitochondria are usually depicted as stiff, elongated cylinders with a diameter of 0.5–1 μm, resembling bacteria. This allows 15 times more ATP to be made than that produced by glycolysis alone. In mitochondria, the metabolism of sugars is completed: the pyruvate is imported into the mitochondrion and oxidized by O 2 to CO 2 and H 2O. When glucose is converted to pyruvate by glycolysis, only a very small fraction of the total free energy potentially available from the glucose is released. Without mitochondria, present-day animal cells would be dependent on anaerobic glycolysis for all of their ATP. The F0 subunit would be the portion of the complex that's embedded in the membrane, and the F1 component would be the part that is sticking out into the matrix.Mitochondria occupy a substantial portion of the cytoplasmic volume of eucaryotic cells, and they have been essential for the evolution of complex animals. Another way of describing this complex is calling it the F0 and F1 subunits, you'll see that terminology as well. And then they come out of that channel into the matrix, and that's how the protons get back into the matrix. And that's where the protons go - they go in through that channel, then they move from one channel to the other and when they move, they drive the c ring to rotate. If you take a close look at the "a" purple unit up at the top, looks like a half moon, you can see two channels in it that go from the outside of the matrix to the inside of the matrix. The purple alpha a, b2, and delta parts on the left are very important because they basically hold the alpha and beta subunits in place so that when the c ring spins it won't just spin the whole thing, it actually spins relative to the rest of it. And it's got a long arm that stretches into the alpha-beta complex - and then when it rotates, it kind of nudges the alpha and beta subunits into various configurations which make the ATP get synthesized out of ADP and phosphate. And you see how that c ring would rotate? It rotates that gamma subunit down there in the middle (that's the red one). The other part, which consists of the purple part on the left - the a, b2, delta, and then also the orange and yellow parts on the bottom, the alpha and beta - all of that is a separate unit which more or less stays in place. Those all rotate - and the rotation of those is driven by the protons, the proton-motive force. There is the c ring and the gamma and epsilon units, that you see (the red and the green units attached to the blue c ring there).
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