Wize University Biology Textbook > The Plasma Membrane
Thermodynamics of Membrane Formation
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Thermodynamics of Membrane Formation
The bilayer formation is stabilized by the hydrophobic effect. By preventing the interaction of non-polar groups with water (which is unfavorable) the entropy of water is increased.
- Enthalpic (ΔH) and Entropic (TΔS) stability contribute to membrane formation.
- Enthalpy refers to bonds that are formed (the more negative, the greater the stability) and entropy refers to molecular motion (the more positive, the greater the stability).
- Gibbs Free Energy (ΔG) can be determined by the formula can be thought of as a measure of instability: all systems tend to minimize ΔG. It is given by the following formula:
ΔG = ΔH + (−TΔS)
- Bilayer formation is spontaneous when ΔG is negative.
Favorability of Bilayer Formation
ΔG = ΔH + (-TΔS)
More freedom of movement = more entropy = bigger TΔS = more negative
ΔG = thermodynamically favorable
- Why is bilayer formation thermodynamically favorable in terms of ΔH?
- Lower energy interactions between lipid tails than water with lipid tails (lower enthalpy).
- Why is there a large ΔS when bilayers form?
- The lipid tails have more freedom to move (higher entropy).
Which enthalpic and entropic combinations will result in a spontaneous bilayer formation?
| Spontaneous (yes/no/depends) | ∆H | T∆S |
| <0 | >0 | |
| <0 | <0 | |
| >0 | >0 | |
| >0 | <0 |