Question

What might happen if you transfer an alpha helix peptide from a lipid environment to an aqueous?

Answer 1

Hydrophobic effect:

The alpha helix is a secondary structure of a peptide which is involved in the folding of the proteins. The hydrogen between the amide and the carbonyl group give rise to the alpha helix backbone in the form of spiral structure. For this protein folding to be successful the folding process must be thermodynamically favourable. As it is a spontaneous process the negative gibbs free energy is dependent on the entropy(high) and enthalpy(low). The environment of the alpha helix formation affects the entropy and enthalpy and also affects the stability of the helix.  So the protein folding tends to occur in a hydrophobic or lipid environment where the entropy is high.

While in an aqueos environment the alpha helix experience a hydrophobic effect (the hydrophobic side chains of a protein collapse into the inner core of a protein) to protect themselves from the hydrophillic environment. The water molecules surrounding the hydrophobic side chains aggregate around it and create a shell of ordered water molecules. This increases the order in the system and hence result in the decrease in the entropy. And so the stability of the peptide also decreases.

To overcome this the fixed water molecules cause the break down of the inward hydrophobic group which results in the increase in the entropy back again.