Tuesday, September 7, 2010

Entropic forces keep you alive

I really like chapter 7, "Entropic forces" in Nelson's Biological Physics: Energy, Information, and Life, the reading for this week in BIPH3001.

Biological question: What keeps cells full of fluid? How can a membrane push fluid against a pressure gradient?

Physical idea: Osmotic pressure is a simple example of an entropic force.

You can learn a lot just from reading the great section headings

7.2.1 Equilibrium osmotic pressure obeys the ideal gas law.

7.2.2 Osmotic pressure creates a depletion force between large molecules

7.3.1 Osmotic forces arise from the rectification of Brownian motion

7.3.2 Osmotic flow is quantitatively related to forced permeation

7.4.1 Electrostatic interactions are crucial for proper cell functioning

7.4.3 Charged surfaces are surrounded by neutralizing ion clouds

7.4.4 The repulsion of like-charged surfaces arises from compressing their ion clouds

7.4.5 Oppositely charged surfaces attract by counterion release

7.5.1 Liquid water contains a loose network of hydrogen bonds

7.5.2 The hydrogen-bond network affects the solubility of small molecules in water

7.5.3 Water generates an entropic attraction between nonpolar objects

1 comment:

  1. Wow. This is heady stuff. I missed this chapter last year because I was involved in Biph2000. I'm glad I made time for it this time around. This is very important stuff!