Biology Question #2859

Kirandeep, a 19 year old female from Ludhiana asks on July 29, 2005,

Why do proteins form lather on making their solutions?

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The answer

Barry Shell answered on August 3, 2005

Proteins are long complicated tangled chains of amino acid molecules. Often to dissolve them they must be denatured somewhat. That means untangled. When this happens they become stretchy and flexible. They also expose hydrophilic and lipophilic parts--water loving and oil loving sections of the chain--which makes them into surfactants. Foaming is caused by the protein film lowering surface tension, i.e. cohesive force of water molecules that tend to collapse a bubble. The protein's surfactant properties also resist shearing and tearing due to the protein's stretching capacity. So when a protein solution is shaken or stirred, air is drawn in and when it tries to escape, it forms millions of bubbles due to the effects of the protein chains. This is the foam you see.

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