In this module:

Besides energy storage and bilayer formation, lipids have several other important functions in the cell.

Anchors for membrane-associated proteins

Many proteins are anchored to membranes in the cell by the covalent attachment of a fatty acid. For example, the viral protein src causes cancer in several organisms. An amide bond is formed between the Gly residue and myristic acid, a fatty acid found in cell membranes. The covalent bond keeps the protein associated with the membrane. The ability of src to cause cancer is blocked if the formation of this peptide bond is prevented.

Click several times on the structure at right to see how the attachment is made.

Source of Vitamins

Several vitamins necessary for higher animal life are only soluble in lipids. Some examples along with their roles in the body are shown below. A diet completely lacking in fat will be deficient in these vitamins, with the effects that are described below.

	Vitamin K1: necessary for blood clotting
	a-Tocopherol (Vitamin E): Prevents the inappropriate oxidation of membrane lipids. Deficiency in Vitamin E also causes infertility in rats.
	Retinol (Vitamin A): necessary for normal juvenile growth. Vitamin A deficiency also leads to night blindness.
	Calciferol (Vitamin D2): a hormone derived from Vitamin D2 is necessary for calcium and phosphorus metabolism.

Why do you suppose these molecules are only soluble in lipids? Enter your answer in the space, then click on the Check button to see the answer.

These vitamins are composed almost entirely of carbon and hydrogen, which have similar electronegativities and nonpolar bonds. This means they are hydrophobic, like the fatty acid tails of lipids.