BIOL 1201 Chapter : Biology 1201 Sec
Document Summary
It is composed of two layers of phospholipids, with hydrophilic heads and hydrophobic tails. A membrane remains fluid as temperature decreases until finally the phospholipids settle into a closely packed arrangement and the membrane solidifies, much as bacon grease forms lard when cooled. The temperature at which a membrane solidifies depends on the types of lipids it is made of. The membrane remains fluid to a lower temperature if it is rich in phospholipids with unsaturated hydrocarbon tails. Membranes must be fluid to work properly; they are usually about as fluid as salad oil. When a membrane solidifies, its permeability changes, and enzymatic proteins in the membrane may become inactive if their activity requires them to move within the membrane. However, membranes that are too fluid cannot support protein function either. One can see similar patterns comparing species with different body temperature or cells grown at different culture temperatures.
