Microbial Metabolism and Ebola: Core Concepts in Microbiology

Microbial Metabolism I & II

Learning Outcomes

Microbial metabolism encompasses the chemical processes that occur within microorganisms to sustain life. Understanding these processes is essential for appreciating microbial growth, energy production, and pathogenicity.

• Distinguish between catabolic and anabolic reactions: Catabolic reactions break down molecules to release energy, while anabolic reactions build complex molecules using energy.

• Describe metabolic pathways: Pathways are sequences of enzymatic reactions that transform substrates into products.

• Explain energy conservation mechanisms: Microbes use various strategies to conserve and utilize energy, including substrate-level phosphorylation, oxidative phosphorylation, and photophosphorylation.

• Classify metabolic types: Based on energy and carbon sources, microbes are categorized as phototrophs, chemotrophs, autotrophs, and heterotrophs.

Big Picture: Metabolism

Definition and Importance

Metabolism refers to the sum of all biochemical reactions occurring within a cell. These reactions are essential for growth, maintenance, and reproduction.

• Anabolism: Building up of complex molecules from simpler ones (requires energy).

• Catabolism: Breakdown of complex molecules into simpler ones (releases energy).

Microbial Nutritional Requirements

What Nutrients Do Microbes Need?

Microbes require a variety of nutrients for growth and metabolism. These nutrients are classified based on the quantity required and their function.

• Macronutrients: Needed in large amounts (e.g., carbon, nitrogen, oxygen, hydrogen, phosphorus, sulfur, potassium).

• Micronutrients: Needed in small amounts (e.g., iron, vitamins, trace metals).

Microbes obtain these nutrients from their environment, and their metabolic capabilities determine which nutrients are essential.

Metabolic Pathways

Overview

Metabolic pathways are series of enzyme-catalyzed reactions that convert substrates into products. The direction and efficiency of these pathways are determined by the enzymes involved.

• Catabolic pathways: Break down molecules, releasing energy.

• Anabolic pathways: Use energy to build complex molecules.

Catabolic Reactions

Catabolic reactions degrade complex molecules into simpler ones, providing energy and building blocks for the cell.

• Example: Breakdown of glucose during glycolysis.

Anabolic Reactions

Anabolic reactions use energy and building blocks to synthesize complex molecules necessary for cell structure and function.

• Example: Synthesis of proteins from amino acids.

Classification of Metabolic Types

Based on Energy Sources

Microbes are classified according to their primary energy source:

• Phototrophs: Use light as an energy source.

• Chemotrophs: Obtain energy from chemical compounds.

Based on Carbon Sources

• Autotrophs: Use carbon dioxide as a carbon source.

• Heterotrophs: Use organic compounds as carbon sources.

Basics of Bioenergetics

Free Energy and Reactions

Bioenergetics studies the flow and transformation of energy in biological systems.

• ΔG°': Standard free energy change.

• ΔG°' > 0: Reaction requires energy (endergonic).

• ΔG°' < 0: Reaction releases energy (exergonic).

• ΔG: Free energy under physiological conditions.

Collision Theory

Chemical reactions occur when molecules collide with sufficient energy and proper orientation. Enzymes increase the frequency and efficiency of these collisions.

• Activation energy is the minimum energy required for a reaction to occur.

Enzymes and Chemical Reactions

Enzymes are biological catalysts that speed up chemical reactions without being consumed.

• Highly specific for their substrates.

• Lower the activation energy of reactions.

• One enzyme, one substrate, one reaction.

Redox Reactions and Energy Conservation

Reduction Potential

Reduction potential measures the tendency of a substance to gain or lose electrons.

• Oxidation: Loss of electrons.

• Reduction: Gain of electrons.

• More negative value: better electron donor.

• More positive value: better electron acceptor.

Reduction Potential and Free Energy

The greater the difference in reduction potential between donor and acceptor, the more energy is released.

NADH as an Electron Carrier

NADH is a key electron carrier in microbial metabolism, transferring electrons between reactions and facilitating energy conservation.

Energy Conservation Mechanisms

Energy-Rich Bonds in Microbial Metabolism

Certain compounds contain energy-rich bonds that are used to conserve energy in microbial cells.

• ATP is the primary energy currency.

• Other compounds: Acetyl phosphate, phosphoenolpyruvate.

Cellular Energy Conservation

Microbes conserve energy through several mechanisms:

• Substrate-level phosphorylation: Direct transfer of phosphate to ADP to form ATP.

• Oxidative phosphorylation: Electrons transferred through electron transport chain, generating ATP via proton motive force.

• Photophosphorylation: Light energy used to generate ATP in photosynthetic organisms.

Substrate-Level Phosphorylation

ATP is generated when a high-energy phosphate group is transferred directly to ADP.

$\text{C-C-C} - O - P + \text{ADP} \rightarrow \text{C-C-C} + \text{ATP}$

Oxidative Phosphorylation

Electrons are transferred from electron donors to acceptors via the electron transport chain, creating a proton gradient that drives ATP synthesis.

Photophosphorylation

Occurs only in light-exposed photosynthetic cells, where light energy is converted into chemical energy through a system of electron carriers.

Ebola Virus: Microbial Pathogenesis

Ebola: A Deadly Threat

Ebola virus is a highly pathogenic virus causing severe hemorrhagic fever in humans and primates. Outbreaks have occurred primarily in Africa, with high mortality rates.

• Transmission: Direct contact with bodily fluids of infected individuals.

• Symptoms: Fever, headache, muscle pain, vomiting, diarrhea, hemorrhage.

Ebola Replication Cycle

The replication cycle of Ebola involves entry into host cells, replication of viral RNA, assembly of new virions, and release from the cell.

Ebola Pathogenesis and Pathophysiology

Ebola virus disrupts immune responses and damages blood vessels, leading to multi-organ failure and hemorrhagic symptoms.

Ebola Reston

Ebola Reston is a strain of Ebola virus identified in the Philippines and the United States, primarily affecting non-human primates.

Microbial Respiration and Fermentation

Respiration vs. Fermentation

Microbes generate energy through respiration (using electron transport chains) or fermentation (without electron transport chains).

• Respiration: Complete oxidation of substrates, high ATP yield.

• Fermentation: Partial oxidation, lower ATP yield.

Glycolysis (Embden-Meyerhof-Parnas Pathway)

Glycolysis is a central metabolic pathway that converts glucose to pyruvate, generating ATP and NADH.

$\text{Glucose} \rightarrow 2\ \text{Pyruvate} + 2\ \text{ATP} + 2\ \text{NADH}$

Fermentation Types

• Lactic acid fermentation: Glucose is converted to lactic acid, regenerating NAD+.

• Alcohol fermentation: Glucose is converted to ethanol and CO2, regenerating NAD+.

The Citric Acid Cycle

Overview

The citric acid cycle (Krebs cycle) is a series of reactions that oxidize acetyl-CoA to CO2, generating NADH, FADH2, and ATP.

$\text{Acetyl-CoA} + 3\ \text{NAD}^+ + \text{FAD} + \text{ADP} + \text{P}_i \rightarrow 2\ \text{CO}_2 + 3\ \text{NADH} + \text{FADH}_2 + \text{ATP}$

Principles of Respiration: Generating Proton Motive Force

Electron transport chains in the cytoplasmic membrane transfer electrons, pumping protons to generate a proton motive force used for ATP synthesis.

• Proton motive force drives ATP synthase.

• Final electron acceptor is often O2 (aerobic respiration) or other molecules (anaerobic respiration).

Summary Table: Classification of Microbial Metabolic Types

Classification Basis	Type	Energy Source	Carbon Source	Example Organism
Energy Source	Phototroph	Light	CO2 or organic compounds	Cyanobacteria
Energy Source	Chemotroph	Chemicals	CO2 or organic compounds	Escherichia coli
Carbon Source	Autotroph	Light or chemicals	CO2	Thiobacillus
Carbon Source	Heterotroph	Light or chemicals	Organic compounds	Staphylococcus aureus

Summary Table: Energy Conservation Mechanisms

Mechanism	Description	ATP Yield	Example
Substrate-level phosphorylation	Direct transfer of phosphate to ADP	Low	Glycolysis
Oxidative phosphorylation	Electron transport chain creates proton gradient	High	Aerobic respiration
Photophosphorylation	Light-driven electron transport	Variable	Photosynthesis

Additional info:

• Some slides referenced diagrams and images (e.g., metabolic pathways, Ebola replication) that are not fully visible; explanations are based on standard microbiology knowledge.

• Tables have been reconstructed to summarize classification and energy conservation mechanisms.