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Chapter 4 Carbon and the Molecular Diversity of Life Lecture Outline Overview: Carbon—The Backbone of Biological Molecules Although cells are 70–95% water, the rest consists of mostly carbon-based compounds. Carbon enters the biosphere when photosynthetic organisms use the sun’s energy to transform CO2 into organic molecules, which are transferred to primary consumers. Carbon accounts for the diversity of biological molecules, which has made possible the wide variety of living things. Proteins, DNA, carbohydrates, and other molecules that distinguish living matter from inorganic material are all composed of carbon atoms bonded to each other and to atoms of other elements. These other elements commonly include hydrogen (H), oxygen (O), nitrogen (N), sulfur (S), and phosphorus (P). Concept 4.1 Organic chemistry is the study of carbon compounds. Organic chemistry focuses on organic compounds containing carbon. Organic compounds can range from simple molecules, such as CH4, to complex molecules such as proteins, which may have molecular masses greater than 100,000 daltons. Most organic compounds contain hydrogen atoms. The overall percentages of the major elements of life (C, H, O, N, S, and P) are quite uniform from one organism to another. Because of carbon’s versatility, these few elements can be combined to build an inexhaustible variety of organic molecules. Variations in organic molecules can distinguish even individuals of a single species. The science of organic chemistry began with attempts to purify and improve the yield of products obtained from organisms. Initially, chemists learned to synthesize simple compounds in the laboratory but had no success with more complex compounds. The Swedish chemist Jons Jacob Berzelius was the first to make a distinction between organic compounds that seemed to arise in only living organisms and inorganic compounds that were found in the nonliving world. Early organic chemists proposed vitalism, the belief that physica