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.


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