Carbon Compounds and Functional Groups

Organic chemistry is the study of compounds of carbon. By 1900, biochemists had classified the organic molecules of life into four primary categories: carbohydrates, lipids,

Table 2.5 Energy-Transfer Reactions in the Human Body

Exergonic Reactions

Reactions in which there is a net release of energy. The products have less total free energy than the reactants did.

Oxidation

Decomposition Catabolism

An exergonic reaction in which electrons are removed from a reactant. Electrons may be removed one or two at a time and may be removed in the form of hydrogen atoms (H or H2). The product is then said to be oxidized. A reaction such as digestion and cell respiration, in which larger molecules are broken down into smaller ones. The sum of all decomposition reactions in the body.

Endergonic Reactions

Reactions in which there is a net input of energy. The products have more total free energy than the reactants did.

Reduction Synthesis Anabolism

An endergonic reaction in which electrons are donated to a reactant. The product is then said to be reduced. A reaction such as protein and glycogen synthesis, in which two or more smaller molecules are combined into a larger one. The sum of all synthesis reactions in the body.

Saladin: Anatomy & I 2. The Chemistry of Life I Text I I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

72 Part One Organization of the Body proteins, and nucleic acids. We examine the first three in this chapter but describe the details of nucleic acids, which are concerned with genetics, in chapter 4.

Carbon is an especially versatile atom that serves as the basis of a wide variety of structures. It has four valence electrons, so it bonds with other atoms that can provide it with four more to complete its valence shell. Carbon atoms readily bond with each other and can form long chains, branched molecules, and rings—an enormous variety of carbon backbones for organic molecules. Carbon also forms covalent bonds with hydrogen, oxygen, nitrogen, sulfur, and other elements.

Carbon backbones carry a variety of functional groups—small clusters of atoms that determine many of the properties of an organic molecule. For example, organic acids bear a carboxyl (car-BOC-sil) group, and ATP is named for its three phosphate groups. Other common functional groups include hydroxyl, methyl, and amino groups (fig. 2.14).

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