Microbial Metabolism: Principles and Pathways

Chapter 8: Microbial Metabolism

Chapter Learning Outcomes

Upon completion of this chapter, students should be able to describe and illustrate the processes of microbial growth and metabolism, including the major metabolic pathways and their regulation.

Defining Metabolism

What is Metabolism?

Metabolism refers to the sum of all chemical reactions that occur within a living organism. These reactions are essential for breaking down substances to release energy and for using that energy to build new cellular components.

• Catabolic reactions break down complex molecules into simpler ones, releasing energy in the process (exergonic reactions).

• Anabolic reactions use energy to build complex molecules from simpler ones (endergonic reactions).

• Amphibolic pathways can function in both catabolic and anabolic processes, serving a dual role in metabolism.

Example: The breakdown of glucose during cellular respiration is a catabolic process, while the synthesis of proteins from amino acids is anabolic.

Metabolic Pathways

Metabolic pathways are sequences of enzymatically catalyzed chemical reactions in a cell. Each pathway is tightly regulated and often interconnected with others.

• Catabolic pathways: Release energy by breaking down larger molecules into smaller ones. Example: Glycolysis.

• Anabolic pathways: Consume energy to construct complex molecules from simpler ones. Example: Protein synthesis.

• Amphibolic pathways: Pathways that can be used for both breaking down and building substances, such as the citric acid cycle.

Energy Coupling and ATP

Catabolic and anabolic reactions are often coupled, meaning the energy released from catabolic reactions is used to drive anabolic reactions. The molecule adenosine triphosphate (ATP) acts as the main energy currency in the cell.

• ATP Structure: Composed of adenine, ribose, and three phosphate groups.

• ATP-ADP Cycling: Removing the terminal phosphate group from ATP (hydrolysis) releases energy and produces ADP (adenosine diphosphate). Cells regenerate ATP from ADP by adding a phosphate group (phosphorylation).

Analogy: ATP is like 'metabolic money'—it is the spendable form of energy for cellular processes.

Additional info:

Further sections in the chapter (not shown in the images) would likely cover enzyme function, regulation, and specific metabolic pathways such as glycolysis, the Krebs cycle, and electron transport chain, as well as fermentation and biosynthetic (anabolic) pathways.