An Introduction to Metabolism
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.