Wednesday, April 8, 2009

Hydrophobic interaction and cell design

One concept that students usually find hard to understand is the concept of hydrophobic interaction and its role in cell design.

The fact that the term itself is really a misnomer probably contributes to this difficulty.

Why a misnomer? Well, the energy that is used during the interaction between hydrophobic molecules actually comes from the hydrophilic molecules. Huh? Ok, let’s put it this way.

Some molecules are hydrophilic or “water loving”. “Hydro-“ means water and “philia” means love. Other molecules like oil on the other hand are hydrophobic or “water fearing”. “Phobia” means fear. However, these terms can be misleading because the molecules do not really fear water. What happens is ... in the presence of water, these molecules tend to join together. Why?

Well, water molecules actually have a greater affinity or greater attraction for each other as compared with any attraction between water and other molecules like oil. Thus, when we place drops of oil in water, the water molecules tend to go together and push or squeeze the oil droplets as far away from the water molecules as possible. This therefore results in the oil droplets joining together to form a bigger drop of oil. This joining together of oil droplets in the presence of water is what is called hydrophobic interaction. This is the reason why oil and water do not mix.

So what is the importance of hydrophobic interaction in cell design?

Let’s go back to what cells are made of. Cells consist primarily of water, proteins, lipids, carbohydrates, nucleic acids and traces of some minerals. Cells are separated from their environment by membranes that are basically phospholipid in nature. Because phospholipids have hydrophobic ends and hydrophilic ends, through hydrophobic interaction they therefore naturally form a double membrane in the presence of water.

Thus we can see that hydrophobic interaction contributes very much to the design of cells. Without membranes, we will never have cells.

The picture I used for my banner in this blog is actually a picture of oil droplets in water. Notice how the droplets naturally form "cell membranes".

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