With this new concept in your students' minds, you can now begin discussing how cells can utilize dehydration synthesis and hydrolysis reactions to build macromolecules consisting of thousands of smaller molecules. these macromolecules will play important roles in the cell's metabolic functions. the first group of macromolecules to be discussed with your students is the lipids. lipids are characterized by long chains of carbons and hydrogen atoms linked by nonpolar bonds. these hydrocarbon chains are nonpolar, hydrophobic (hydro- meaning "water" and -phobic meaning "afraid of") macromolecules, which is the causal factor responsible for many of the important functional characteristics of lipids. these long chains can be differentiated from one another by the number of carbons present, the degree of saturation (every carbon atom in the fatty acid chain has two hydrogen atoms bound to it), and the terminal carboxyl group, which is used to classify lipids into different classes of fatty acids. triglycerides and phospholipids are two types of lipids with similar configurations and important biological roles. triglycerides are formed by a series of dehydration reactions that join three fatty acid chains to a three-carbon molecule of glycerol. alternatively, a phospholipid is formed when a glycerol molecule is bound to two fatty acid chains and a phosphate group. since triglycerides and phospholipids are similar in construction and structure, they also share many functional properties. in both molecules, the glycerol "head" is hydrophilic and the fatty acid "tails" are hydrophobic, which gives the macromolecule an amphipathic nature--that is, the presence of opposing properties within one molecule.