Microbiology Exam Study Guide: Key Concepts and Processes

History and Foundations of Microbiology

Key Historical Concepts

This section covers foundational discoveries and theories that shaped microbiology as a science.

• History of Microbiology: Understand major scientists and their contributions (e.g., Pasteur, Koch, Leeuwenhoek).

• Debunking Spontaneous Generation: The process by which the idea that life arises from non-living matter was disproven.

• Germ Theory of Disease: The concept that microorganisms are the cause of many diseases.

• Koch’s Postulates: Criteria to establish a causative relationship between a microbe and a disease.

Cellular Diversity and Classification

Prokaryotes vs. Eukaryotes

Understanding the differences between these two major cell types is fundamental in microbiology.

• Prokaryotes: Cells without a nucleus (e.g., Bacteria, Archaea).

• Eukaryotes: Cells with a nucleus (e.g., Fungi, Protozoa, Algae).

• Genetic Differences: Prokaryotes have circular DNA, eukaryotes have linear chromosomes.

Viruses vs. Cells

• Viruses: Acellular entities that require a host cell to replicate; contain either DNA or RNA.

• Cells: Living units capable of independent metabolism and reproduction.

Evolutionary Relationships

• Woese Paper: Introduced the three domains of life (Bacteria, Archaea, Eukarya) based on rRNA analysis.

• Domains of Life: Classification based on genetic and biochemical characteristics.

Microbial Metabolism and Nutrition

Energy and Carbon Sources

Microorganisms are classified by how they obtain energy and carbon.

• Chemotrophs: Obtain energy from chemical compounds.

• Phototrophs: Obtain energy from light.

• Chemoorganotrophs: Use organic chemicals for energy.

• Chemolithotrophs: Use inorganic chemicals for energy.

• Photoautotrophs: Use light and CO2 as a carbon source.

Microscopy and Cell Morphology

Microscope Types and Uses

• Light Microscopes: Used for viewing stained or live cells.

• Electron Microscopes: Provide higher resolution for ultrastructural details.

Bacterial Cell Morphology

• Cocci: Spherical bacteria.

• Rods (Bacilli): Cylindrical bacteria.

• Spirilla/Spirchetes: Spiral-shaped bacteria.

Cell Structure and Function

Cell Membrane and Wall

• Cell Membrane: Composed of phospholipids and proteins; functions as a selective barrier.

• Cell Wall: Provides structural support; differences exist between Gram-positive and Gram-negative bacteria.

• Archaeal Membranes: Differ in lipid composition and structure from bacterial membranes.

Transport Systems

• Simple Transport: Driven by energy from the proton motive force.

• Group Translocation: Chemical modification of the transported substance.

• ABC Transport Systems: Use ATP to transport substances across membranes.

Cell Wall and Outer Membrane

• Peptidoglycan: Main component of bacterial cell walls; thickness varies between Gram-positive and Gram-negative bacteria.

• Outer Membrane (Gram-negative): Contains lipopolysaccharide (LPS), which acts as an endotoxin.

• Periplasm: Space between the inner and outer membranes in Gram-negative bacteria.

Surface Structures

• Capsule: Polysaccharide layer outside the cell wall; protects against desiccation and phagocytosis.

• Pili: Hair-like appendages for attachment or conjugation.

• Inclusion Bodies: Storage sites for nutrients.

Endospores

• Definition: Highly resistant, dormant structures formed by some bacteria for survival under adverse conditions.

• Vegetative Cell vs. Endospore: Endospores are metabolically inactive and highly resistant; vegetative cells are active and sensitive to environment.

Bacterial Motility and Chemotaxis

Flagella and Motility

• Flagella Types:

  • Polar: Single flagellum at one or both ends.

  • Peritrichous: Flagella distributed over the entire cell.

  • Lophotrichous: Cluster of flagella at one or both ends.

  • Amphitrichous: Single flagellum at both ends.

• Flagella Structure: Composed of filament, hook, and basal body; rotation driven by proton motive force.

• Flagella Motor: Functions like a rotary engine; Mot proteins act as a clutch.

Chemotaxis

• Definition: Movement of bacteria in response to chemical gradients.

• Mechanism: Bacteria sense attractants or repellents and adjust their movement accordingly.

Bioenergetics and Metabolism

Bioenergetics

• Aerobic vs. Anaerobic Respiration: Aerobic uses oxygen as the final electron acceptor; anaerobic uses other molecules.

• Chemotrophs vs. Chemoorganotrophs: Chemotrophs use chemical energy; chemoorganotrophs use organic compounds.

• Redox Reactions:

  • Endergonic: Requires energy input.

  • Exergonic: Releases energy.

  • Oxidation: Loss of electrons.

  • Reduction: Gain of electrons.

  • Redox Tower: Ranks electron carriers by reduction potential; strongest electron acceptor is at the bottom.

• High-Energy Bonds: ATP and other molecules store energy in high-energy phosphate bonds.

Catabolism of Glucose: Cellular Respiration and Fermentation

• Role of Coenzymes: Molecules like NAD+ shuttle electrons during metabolic reactions.

• Major Steps: Glycolysis, Krebs cycle, electron transport chain.

• ATP Synthase: Enzyme that uses proton gradient to synthesize ATP from ADP and Pi.

• Alternative Pathways: Some bacteria use pathways other than glycolysis (e.g., Entner-Doudoroff pathway).

• Fermentation: Anaerobic process that regenerates NAD+ and produces end products like lactic acid or ethanol.

Key Equation for Cellular Respiration:

$C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{energy (ATP)}$

Laboratory Techniques

Aseptic Technique

• Definition: Procedures to prevent contamination of cultures and sterile media.

Staining Methods

• Simple Stain: Uses a single dye to color cells.

• Negative Stain: Stains the background, leaving cells clear.

• Gram Stain: Differentiates bacteria into Gram-positive (purple) and Gram-negative (pink) based on cell wall structure.

Diluting Bacteria (Streak Plate Method)

• Purpose: To isolate single colonies from a mixed culture.

• Method: Sequentially streaking bacteria across an agar plate to dilute the sample.

Additional info:

• Some details, such as specific scientist names or alternative catabolic pathways, were inferred for completeness.

• For a deeper understanding, refer to your textbook or lecture notes for diagrams and more detailed mechanisms.