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ID#: 54264	Area: Posts	Submitted: 2009-10-26 18:45:53	Posted: 2009-11-03 03:01:04
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QDear 100 Hour Board,

I. feel. dumb. I must have been tired when I was writing my question about alpha-helical structures (stairs in particular). My main question really was: what is the physical reasoning behind the awesome stability of these structures?

- Volleyball

ADear Volleyball,

For those who are wondering, the previous question referenced was Board Question #54102.

Your question is somewhat problematic because a true alpha helix does not have a supporting central pole like most spiral staircases do. The term "alpha helix" originated in microbiology and describes a common structure found in folded proteins. In a biological context, an alpha helix is somewhat like a tightly-wound spring with periodic vertical links between "levels." The center of the helix is very crowded, but there's not actually a central core.

Comparing the stability of a biological alpha helix to that of a staircase is difficult, though. Molecular stability has more to do with how likely it is to bond with something else than it does with how well it keeps its shape. In fact, molecular alpha helices are commonly curved, and sometimes are even themselves wrapped into a higher-order helix. I think you'd agree that a spiral staircase that bent back on itself to that degree would hardly be characterized as stable.

Spiral staircases are stable because of a solid central core and an outer curved panel that distributes local pressure throughout the structure. Molecular alpha helices are stable because it takes a fair amount of energy to break one of the existing bonds in order to form a new one. However, alpha helices tend to unravel when placed in aqueous solutions due to the high reactivity of water molecules. (See Wikipedia for a more technical description of what I just tried to say.)

(Dear chemistry and biology majors: please don't hate me for that last paragraph. I'm neither a chemist nor a biologist.)

So, dearest volleyball, I guess I'm left wondering what source you have that indicates that the stability of spiral staircases is due to alpha helices.

-Yellow

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