Remember, I mentioned in one of my earliest posts that cell membranes are my favourite part of the cell (Nov 1, my favourite part of the cell)? Today, I’d like to go back to cell membranes. Why? Well, the cold weather reminded me about what cells do to their membranes when their surroundings get cold.
As you probably know, cell membranes are basically made up of phospholipid bilayers. Then proteins are inserted into this phospholipid bilayer either half-way through or all the way through (please the diagrams above).
Most of the time, the phospholipid molecules in the membrane are fully saturated, so their “tails” appear straight as shown in diagram A. When the temperature gets cold however, the cells replace the saturated phospholipid molecules with unsaturated ones. The unsaturation or addition of double bonds in these molecules produce “kinks” in their “tails” (please see diagram B).
So what is the significance of these “kinks” in the phospholipid molecules? Well, because of the kinks, the molecules become harder to compress and therefore also harder to crystallize. Molecules have to be close together in order to crystallize them. If they are far apart, they cannot be crystallized. This process thus protects the cells because their membrane remains fluid and substances can still go in or out of cells. The same thing is impossible if the molecules are crystallized.
So when it’s cold, cells put on “kinky” membranes in order to survive. Isn’t that cool? (pun intentional)
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