Bio Ques

[HistoRocks]

How does having a folded inner membrane increase the surface area of the mitochondria? When I looked at the illustration, it seemed like having a flat surface would actually maximize the surface area, assuming the outer membrane of the mitochondria retains a constant shape. Is it just the outer membrane folding on the inside? Without which, there would simply be no inner portion of mitochondria? The cerebral cortex does the same thing, but in that case it makes sense, coz' the gyri are convoluted.

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[MattD]

How does having a folded inner membrane increase the surface area of the mitochondria? When I looked at the illustration, it seemed like having a flat surface would actually maximize the surface area, assuming the outer membrane of the mitochondria retains a constant shape. Is it just the outer membrane folding on the inside? Without which, there would simply be no inner portion of mitochondria? The cerebral cortex does the same thing, but in that case it makes sense, coz' the gyri are convoluted.

Hmm, I'm not really sure how to answer this one without drawing a picture... Try this game: take a piece of tin foil and crumple it, not into a ball, leave it in the form of a sheet, just with crumples all over it. Now take another sheet of foil and lay the crumpled piece on top of it, and cut the new sheet to the same outside dimensions as the crumpled sheet. Now, they should both have the same 'footprint'. So which has the most surface area? The crumpled one obviously does, and you can prove it by grabbing the edges of the crumpled one and pulling on it to smooth out the crumples. Now that piece is BIGGER than the other one, therefore it must have had a bigger surface area all along. Same thing with the mitochondrial membrane, just in 3D. This is the same concept as why the intestines have ciliated villi. The villi cause the intestines to have a much larger surface area than a smooth tube would have, and the cilia make it even bigger!