(9/22/99) 24. I have a sentence in my notes: Hydrogen bonds are readily broken by temperatures between 0 degrees C and 100 degrees C. Gas exists at the temperature at which no hydrogen bonding is possible. Anyway, why aren't a lot of hydrogen bonds broken by body temperature (98.6 degrees)?
Yes, individual H-bonds are being broken (and re-formed) all the time, in the water present in your body, for example. But when these bonds are broken in a molecule like the alpha-helix of a polypeptide, at any moment in time there are still many others that continue to hold the alpha helix in its helical conformation. That is, at any given moment in time, only a minority of the H-bonds will be broken, while the rest hold the structure together. At the next moment it is another set that is doing the breaking and while others are doing the holding. Thus an alpha helix of some minimum length is stable at body temperature.