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Chapter 8 An Introduction to Metabolism Lecture Outline Overview: The Energy of Life Concept 8.1 An organism’s metabolism transforms matter and energy, subject to the laws of thermodynamics. The totality of an organism’s chemical reactions is called metabolism. Metabolism is an emergent property of life that arises from interactions between molecules within the orderly environment of the cell. The chemistry of life is organized into metabolic pathways. A metabolic pathway begins with a specific molecule, which is then altered in a series of defined steps to form a specific product. A specific enzyme catalyzes each step of the pathway. Catabolic pathways release energy by breaking down complex molecules to simpler compounds. A major pathway of catabolism is cellular respiration, in which the sugar glucose is broken down in the presence of oxygen to carbon dioxide and water. The energy released by catabolic pathways becomes available to do the work of the cell, such as ciliary beating or membrane transport. Anabolic pathways, also called biosynthetic pathways, consume energy to build complicated molecules from simpler compounds. The synthesis of protein from amino acids is an example of anabolism. Energy released from the downhill reactions of catabolic pathways can be stored and then used to drive the uphill reactions of anabolic pathways. Energy is fundamental to all metabolic processes, and therefore an understanding of energy is key to understanding how the living cell works. Bioenergetics is the study of how energy flows through living organisms. Organisms transform energy. Energy is the capacity to cause change. In everyday life, some forms of energy can be used to do work—that is, to move matter against opposing forces, such as gravity and friction. Energy exists in various forms, and cells transform energy from one type to another. Kinetic energy is the energy associated with the relative motion of objects. Objects in motion can perform work by imparting mot