New
Discovery in ATP Synthase
Background Information
Role
of ATP Sythase in the Cell
Background Information
ATP Synthase is found in the inner membrane of mitochondria. Mitochondria are small compartments within cells that contain much of the machinery responsible for cellular energy production. ATP Synthase is one of the pieces of machinery involved in this process.
Figure : This is an electron micrograph of a mitochondrion. Mitochondria are rod-shaped organelles in cells that contain ATP Synthase (and other cellular energy production machinery). (Spurger 2002).
The buildup of protons on one side of the membrane leads to a difference in concentration and charge on both sides of the inner mitochondrial membrane. The natural state for a solution of ions is to have charges and molecules equally dispersed, but because this is not the case in this situation, the protons "want" to get to the other side of the membrane to equalize the concentration and charge on both sides. The only way that the protons can get through the membrane is to pass through the F0 pore of the ATP Synthase complex. To pass through this pore, protons must do work (use energy) and turn the rod of the F1, which in turn induces a change in each of the active site subunits. This describes the rotational model of ATP Synthase.
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Figure 2: ATP Synthase with Fo and F1 subunits and Proton Gradient. This figure shows the difference in the concentration of protons (H+) on either side of the phospholipid bilayer. Notice the large concentration of protons on one side of the bilayer that flow through ATP Synthase to the less concentrated side by fascilitated diffusion. Also note the parts of the enzyme denoted Fo and F1, as well as the individual subunits including the alpha, beta, gamma and c subunits (image from Wikepedia). |
The F1 part of ATP Synthase has 5 subunits: alpha, beta, gamma, delta and epsilon. Alpha and beta subunits (3 each) alternate with each other to form a circular structure, as shown in Figure *********above. The beta subunits have the active site for ATP synthesis. In the middle of this circle of protein subunits is the gamma subunit, which is asymmetrically shaped, and though it fits tightly into the middle, when it moves it alters the conformation of the beta subunits in a cyclic pattern. The delta subunit is rod-shaped and extends vertically on the outside of the circle of alpha and beta subunits, holding F1 and F0 together, in a sense anchoring F1 so that it cannot move. The epsilon subunit is attached to and extends down from the gamma subunit, and is in contact with the F0 part of ATP Synthase.
F0 has three subunits, a, b, and c. There are 10 to 12 c subunits arranged in a circle forming the c ring. The b subunit is attached to the alpha subunit, which is stationary and anchored to the membrane, and the delta subunit of F1.