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Chapter 5 The Structure and Function of Macromolecules Lecture Outline Overview: The Molecules of Life Within all cells, small organic molecules are joined together to form larger molecules. All living things are made up of four main classes of macromolecules: carbohydrates, lipids, proteins, and nucleic acids. These large macromolecules may consist of thousands of covalently bonded atoms, some with mass greater than 100,000 daltons. Biochemists have determined the detailed structures of many macromolecules, which exhibit unique emergent properties arising from the orderly arrangement of their atoms. Concept 5.1 Most macromolecules are polymers, built from monomers. Three of the four classes of macromolecules—carbohydrates, proteins, and nucleic acids—form chain-like molecules called polymers. A polymer is a long molecule consisting of many similar or identical building blocks linked by covalent bonds. The repeated units are small molecules called monomers. Some of the molecules that serve as monomers have other functions of their own. The chemical mechanisms that cells use to make and break polymers are similar for all classes of macromolecules. Monomers are connected by covalent bonds that form through the loss of a water molecule. This reaction is called a condensation reaction or dehydration reaction. When a bond forms between two monomers, each monomer contributes part of the water molecule that is lost. One monomer provides a hydroxyl group (—OH), while the other provides a hydrogen atom (—H). Cells invest energy to carry out dehydration reactions. Dehydration is facilitated by enzymes, specialized macromolecules that speed up chemical reactions in cells. The covalent bonds that connect monomers in a polymer are disassembled by hydrolysis, a reaction that is effectively the reverse of dehydration. In hydrolysis, bonds are broken by the addition of water molecules. A hydrogen atom attaches to one monomer, and a hydroxyl group attaches to the adjacent monomer