Polypeptide is both hydrophilic and hydrophobic. What will happen when it is added to water?

1 Answer
Apr 17, 2018

Hydrophobic Effect will occur. I'll explain below.


A polypeptide may be hydrophobic and hydrophillic because of the R-groups on each amino acid. Some amino acids are very non-polar, and some are very polar/H-bonding/Ionic.

Lets imagine a small bit of oil on top of water. If you stir this water vigorously, the oil will break up into tiny oil droplets.

When it is in the tiny oil droplets state, this is like having a polypeptide in water. The hydrophobic amino acids are like the tiny oil droplets.

When you let the oil/water mix sit for a few moments, the oil droplets form into a larger oil droplet. This reduces their surface area contact with water.

The same process happens with proteins. The hydrophobic amino acids want to get out of water, so they all go to the center and form a hydrophobic core. This process is called the "hydrophobic effect", and it is the main driving force for protein folding (thermodynamically speaking). Once the hydrophobic amino acids are out of water and the protein is roughly in a 3D structure, the polar/H-bonding amino acids can then interact to help hold the protein together better.