Microbial Metabolism: Foundations and Pathways

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CH 5: Microbial Metabolism

Introduction to Microbial Metabolism

Microbial metabolism encompasses all the chemical reactions that occur within a microorganism, enabling it to grow, reproduce, and respond to its environment. These reactions are essential for converting nutrients from the environment into energy and cellular components.

Growth Medium: Provides essential nutrients (such as carbohydrates, lipids, and proteins) for microbial growth, as illustrated by Escherichia coli cultures.
Metabolic Reactions: The sum of all chemical processes, including catabolism (breakdown of molecules) and anabolism (synthesis of molecules).
Energy Source: Metabolism is fueled by the energy and building blocks provided by the medium.

Learning Objectives

Define metabolism and distinguish between catabolism and anabolism.
Describe the role of ATP as an energy intermediary.
Explain oxidation-reduction (redox) reactions.
Identify and provide examples of three types of phosphorylation reactions that generate ATP.
Describe the function of metabolic pathways.
Explain glycolysis and its chemical reactions.
Identify the functions of the pentose phosphate and Entner-Doudoroff pathways.
List the products of the Krebs cycle.
Describe the chemiosmotic model for ATP generation.
Compare aerobic and anaerobic respiration.
Describe fermentation and its products.
Compare cyclic and noncyclic photophosphorylation.
Contrast light-dependent and light-independent reactions of photosynthesis.
Compare oxidative phosphorylation and photophosphorylation.
Summarize energy production in cells.
Categorize nutritional patterns among organisms based on carbon source and ATP generation mechanisms.

Metabolism

Definition and Organization

Metabolism is the sum total of all chemical reactions in a cell. These reactions are enzyme-catalyzed and organized into regulated pathways, where each step is facilitated by a specific enzyme.

Catabolic Pathways: Break down complex molecules into simpler ones, releasing energy (exergonic).
Anabolic Pathways: Build complex molecules from simpler ones, requiring energy input (endergonic).
Pathways are often depicted as a series of enzyme-mediated steps: Enzyme 1 → Enzyme 2 → Enzyme 3, etc.

Catabolism vs. Anabolism

Catabolism: Degradative, energy-yielding processes (e.g., glycolysis, respiration).
Anabolism: Biosynthetic, energy-consuming processes (e.g., protein synthesis, DNA replication).

ATP: The Energy Currency of the Cell

Structure and Function

Adenosine triphosphate (ATP) is the primary molecule for storing and transferring energy in cells. It consists of adenine, ribose, and three phosphate groups.

ATP Hydrolysis: Releases energy for cellular work (catabolic process).
ATP Formation: Requires energy input (anabolic process).

Key Reactions Involving ATP/ADP

ATP Hydrolysis (energy-releasing):

ATP Synthesis (energy-requiring):

ATP acts as an energy intermediary, linking catabolic and anabolic reactions.

Summary Table: Catabolism vs. Anabolism

Process	Catabolism	Anabolism
Function	Breaks down molecules	Builds up molecules
Energy	Releases energy (exergonic)	Requires energy (endergonic)
Example	Glycolysis, respiration	Protein synthesis, DNA replication

Key Terms

Metabolism: All chemical reactions in a cell.
Catabolism: Energy-releasing breakdown of molecules.
Anabolism: Energy-consuming synthesis of molecules.
ATP: Main energy carrier in cells.
Enzyme: Protein catalyst that speeds up chemical reactions.

Example: E. coli Growth in a Medium

Scenario: E. coli is incubated in a nutrient-rich medium.
Process: The medium provides carbohydrates, lipids, and proteins, which are metabolized for energy and growth.
Outcome: Through catabolic and anabolic reactions, E. coli cells grow and divide, as shown in the time-lapse images.