18e: Super Complex

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Electron Transport:

Supercomplex I1III2IV1– A Multienzyme

Electron Pathway

Fill in the blanks on the following statement:

In electron transport, the electrons from ____________ are transferred via complex I (NADH:ubiquinone oxidoreductase) and ubiquinone to complex _____ (ubiquinol:cytochrome c oxidoreductase). Thereafter they pass through cytochrome c to complex _____ (cytochrome c oxidase) to the terminal acceptor, ______________.

Multienzyme

In many organisms, this pathway is assembled into a supercomplex.

Schäfer, Dencher, Vonck and Parcej, Biochemistry, 2007, 46, 12579-12585.

In terms of electron transfer rates and entropy, explain why is a supercomplex might be an advantage to an organism.

This is a 3D map of the Supercomplex I1III2IV1 along the membrane plane.

Identify the three individual protein complexes:
- Complex I
- Complex III
- Complex IV

On the basis of the fitted structure, cytochromes b and c₁ from complex III₂ seem to face subunit II. Hence, the cytochrome c binding sites of both complexes are facing each other (shown below).

Screen Shot 2019-05-13 at 1.29.49 PM.png

Based on this picture of the supercomplex, speculate about the diffusion of the mobile electron carriers. How mobile are these carriers? Are the substrates directly channeled? Diffused over a short distance?