This results in a structure which has a hydrophobic core and two hydrophilic surfaces. The lipid molecules involved are phospholipids. We'll look at their typical structures shortly. Proteins are also embedded in the membrane, anchored there by hydrophobic interactions between the hydrophobic side chains of certain of their amino acids and the tails of the phospholipids. Some proteins extend through the membrane, as we saw for those involved in oxidative phosphorylation, and some do not, as in the respiratory chain.
Some proteins have carbohydrate segments attached which extend into the aqueous environment.
Proteins which extend through the membrane often serve as receptors for hormones and transmitters of the message to the interior. They can also serve as gates or channels which regulate the passage of small molecules through the membrane. Phospholipids come in several types, all of which include a phosphate ester linkage, a polar head and two hydrocarbon tails. The specifics of how these units are joined and the structure of the polar head determine which of the main phospholipic classes a particular molecule fits. Glycerophospholipids resemble fats in that they are esters of glycerol.