Chapter 2, Problem 2.20YT

Interpretation Introduction

Interpretation:

The hydrophobic regions in Figure 2-31a and 2-31b are to be identified and labeled.

Concept introduction:

Phospholipids consist of glycerides in which two of the hydroxide groups are esterified by fatty acid molecules. The third one is a phosphate ester $-{\text{CH}}_{\text{2}}-\text{O}-{\text{PO}}_{\text{3}}{}^{-}$. The two fatty acid ester groups have long hydrocarbon chains and are, therefore, hydrophobic. The phosphate group is ionic and, therefore, hydrophilic. In an aqueous environment, such phospholipids aggregate to form bilayers. The hydrophilic phosphate groups are strongly solvated by water molecules and form the outer surfaces of the bilayer. The hydrophobic “tails,” i.e., the hydrophobic hydrocarbon chains, are on the inside, away from the aqueous environment.