The chapter also describes the basic organic molecules of living organisms. Cells use carbohydrates, made up of polymers of glucose, primarily as energy sources. Lipids, combinations of glycerol and fatty acids, are important in long-term energy storage. Plasma membranes are composed of phospholipids, a special type of lipid containing a phosphate group. Certain hormones, like steroids, are also lipids. Proteins are made up of long, twisted chains of amino acids. Proteins serve a wide variety of functions in cells and can have complex folded structures. Nucleic acids, such as DNA and RNA, are polymers of nucleotides that store genetic information and transport it within the cell. ATP, the energy currency of the cell, is a nucleotide.
An Ecology Focus on the effects of acid rain and a Health Focus on nutrition labels on foods help students apply knowledge gained from the study of chapter topics.