Quantitative Physiology I / Molecular and Cellular Systems; BMEN E4001x
Notes: 05 – Entropy
Here, we investigate a complementary phenomenon to diffusion, namely entropy.
You’ve probably seen this in terms of the Gibbs free energy for a given reaction:
but what the heck does this mean? From earlier encounters with this term, it should increase.
Vaguely, entropy is disorder, and it is an appropriate statement, as it really has different
implications in different fields, and from different approaches.
It is, to be sure, a
thermodynamic property, such as temperature and enthalpy, but a bit harder to get a hold on.
Temperature, it turns out, is equally intangible, but we interact with it on a more day-to-day
Where will we see entropy in molecular biology? It is a force as equally important as diffusion in
driving molecular recognition.
In Biol 2005 and in subsequent places, you will see examples
of proteins interfacing.
This must happen quickly, and quite often, be reversible.
covalent modifications are one route.
But to take advantage of thermal fluctuations, the
barriers to interaction must be much less than that associated with covalent binding.
the realm of hydrogren binding, hydrophilic/hydrophobic forces, and entropy.
Proteins really important in the immune response. A major type of these
proteins, IgG, has a Y-shape, with a very archetypical structure; two antigen binding sites
(called Fab sites) and a constant region (Fc region). So why have two binding sites?