Microbiology Exam I Review: Foundations, Cell Structure, Microscopy, and Metabolism

The Microbial World and You

Contributions of Key Scientists

• Paul Ehrlich: Developed the concept of chemotherapy; discovered Salvarsan, the first synthetic antimicrobial drug for syphilis.

• Louis Pasteur: Disproved spontaneous generation with his swan-neck flask experiment; developed pasteurization; contributed to vaccine development (rabies, anthrax).

• Robert Koch: Established Koch's postulates, linking specific microbes to specific diseases; discovered the causative agents of tuberculosis and anthrax.

• Edward Jenner: Developed the first successful vaccine (smallpox) using material from cowpox lesions.

• Anton van Leeuwenhoek: First to observe and describe microorganisms ("animalcules") using a simple microscope.

• Robert Hooke: First to use the term "cell" after observing cork; contributed to cell theory.

• Carl Woese: Proposed the three-domain system based on ribosomal RNA sequencing (Bacteria, Archaea, Eukarya).

• Carolus Linnaeus: Developed binomial nomenclature and the hierarchical system of classification.

• Alexander Fleming: Discovered penicillin, the first true antibiotic.

• John Needham: Conducted experiments that seemed to support spontaneous generation, later disproved by Pasteur.

Biogenesis vs. Spontaneous Generation

• Biogenesis: The principle that living organisms arise only from pre-existing life.

• Spontaneous Generation: The (disproven) idea that life can arise from nonliving matter.

• Key Experiments:

  • Redi's Experiment: Showed that maggots do not arise from decaying meat unless flies can lay eggs on it.

  • Needham's Experiment: Boiled broth, then sealed it; observed microbial growth, supporting spontaneous generation (due to inadequate sterilization).

  • Spallanzani's Experiment: Boiled broth longer and sealed flasks; no growth observed, supporting biogenesis.

  • Pasteur's Swan-Neck Flask Experiment: Broth remained sterile in flasks with curved necks, disproving spontaneous generation.

Key Terms and Concepts

• Cell Theory: All living things are composed of cells; cells are the basic unit of life; all cells arise from pre-existing cells.

• Aseptic Technique: Procedures that prevent contamination by unwanted microorganisms.

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

• Vaccination: Administration of a harmless form of a pathogen to induce immunity.

Scientific Nomenclature

• Binomial Nomenclature: Each organism is given a two-part name: Genus (capitalized) and specific epithet (lowercase), both italicized (e.g., Escherichia coli).

Classification of Microorganisms

Carl Woese's Three-Domain System

• Bacteria: Prokaryotic, cell walls contain peptidoglycan.

• Archaea: Prokaryotic, cell walls lack peptidoglycan, often extremophiles.

• Eukarya: Eukaryotic organisms (protists, fungi, plants, animals).

Observing Microorganisms Through a Microscope

Parts and Functions of a Microscope

• Ocular Lens (Eyepiece): Magnifies the image, usually 10x.

• Objective Lenses: Primary lenses (4x, 10x, 40x, 100x) for magnification.

• Stage: Holds the slide.

• Condenser: Focuses light on the specimen.

• Diaphragm: Controls the amount of light.

• Coarse/Fine Focus: Adjusts the focus.

• Total Magnification: Product of ocular and objective lens magnifications.

• Resolution: Ability to distinguish two points as separate.

• Refraction: Bending of light as it passes through different media.

• Pathway of Light: Light source → condenser → specimen → objective lens → ocular lens → eye.

• Metric Conversions: 1 mm = 1000 μm; 1 μm = 1000 nm.

Types of Microscopes

• Brightfield: Standard light microscope; best for stained specimens.

• Darkfield: Enhances contrast in unstained samples; background is dark.

• Phase Contrast: Enhances contrast in transparent specimens; useful for live cells.

• Confocal: Uses lasers for optical sectioning; produces 3D images.

• Fluorescence: Uses fluorescent dyes; detects specific structures or molecules.

• TEM (Transmission Electron Microscope): High-resolution images of internal structures.

• SEM (Scanning Electron Microscope): 3D images of surfaces.

Staining Techniques

Types and Principles of Staining

• Smear: Thin film of specimen on slide.

• Fixing: Attaches microbes to slide and kills them.

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

• Negative Stain: Stains background, not cells; useful for capsules.

• Gram Stain: Differentiates bacteria by cell wall structure (Gram-positive: purple; Gram-negative: pink).

• Acid-Fast Stain: Identifies mycobacteria (e.g., Mycobacterium tuberculosis).

Functional Anatomy of Prokaryotic and Eukaryotic Cells

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic Cells: No nucleus, no membrane-bound organelles, smaller size, circular DNA.

• Eukaryotic Cells: Nucleus, membrane-bound organelles, larger size, linear DNA.

Prokaryotic Structures and Functions

• Capsule: Gelatinous outer layer; protects against phagocytosis.

• Endospores: Resistant structures for survival in harsh conditions.

• Glycocalyx: Polysaccharide layer; aids in attachment and protection.

• Flagella: Motility structures; rotate to propel cell.

• Cell Wall: Provides shape and protection; Gram-positive (thick peptidoglycan), Gram-negative (thin peptidoglycan, outer membrane).

• Ribosomes: Protein synthesis (70S in prokaryotes).

• Plasma Membrane: Selective barrier; site of metabolic processes.

• Fimbriae: Short, hair-like; attachment to surfaces.

• Pili: Longer; involved in conjugation (DNA transfer).

Eukaryotic Structures and Functions

• Nucleus: Contains DNA.

• Mitochondria: ATP production.

• Endoplasmic Reticulum: Protein and lipid synthesis.

• Golgi Apparatus: Modifies and packages proteins.

• Lysosomes: Digestive enzymes.

• Cytoskeleton: Structural support and movement.

Bacterial Shapes and Arrangements

• Shapes: Cocci (spherical), bacilli (rod-shaped), spirilla (spiral).

• Arrangements: Chains (strepto-), clusters (staphylo-), pairs (diplo-).

Chemical Principles and Transport

Osmosis and Transport Mechanisms

• Osmosis: Movement of water across a selectively permeable membrane.

• Hypertonic: Higher solute concentration outside; cell shrinks.

• Hypotonic: Lower solute concentration outside; cell swells.

• Isotonic: Equal solute concentrations; no net water movement.

• Passive Transport: No energy required (diffusion, facilitated diffusion, osmosis).

• Active Transport: Requires energy (ATP); moves substances against concentration gradient.

Microbial Metabolism

Enzymes and Metabolic Pathways

• Active Site: Region on enzyme where substrate binds.

• Substrate: Molecule acted upon by enzyme.

• Allosteric Site: Site other than active site; binding changes enzyme activity.

• Metabolism: All chemical reactions in a cell.

• Catabolic Reactions: Break down molecules; release energy.

• Anabolic Reactions: Build molecules; require energy.

• Enzyme Structure:

  • Holoenzyme: Complete, active enzyme (apoenzyme + cofactor).

  • Apoenzyme: Protein portion.

  • Coenzyme: Organic cofactor (e.g., NAD+).

  • Cofactor: Non-protein component (metal ion or coenzyme).

• Denaturation: Loss of enzyme structure and function due to extreme conditions.

Oxidation and Reduction

• Oxidation: Loss of electrons.

• Reduction: Gain of electrons.

• Redox Reaction: Coupled oxidation and reduction.

ATP Generation

• Substrate-Level Phosphorylation: Direct transfer of phosphate to ADP.

• Oxidative Phosphorylation: Electron transport chain; chemiosmosis.

• Photophosphorylation: Light-driven ATP synthesis (photosynthesis).

Cellular Respiration in Bacteria

• Glycolysis: Glucose → 2 pyruvate; occurs in cytoplasm; produces ATP and NADH.

• Pyruvate Oxidation: Pyruvate → Acetyl-CoA; produces NADH and CO2.

• Krebs Cycle: Acetyl-CoA → CO2; produces NADH, FADH2, ATP.

• Oxidative Phosphorylation: Electron transport chain and chemiosmosis; major ATP production.

• Locations: All processes occur in cytoplasm or plasma membrane in prokaryotes; in mitochondria in eukaryotes.

• Pentose Phosphate Pathway: Alternative to glycolysis; produces NADPH and pentoses.

• Entner-Doudoroff Pathway: Alternative glycolytic pathway in some bacteria.

Fermentation and Anaerobic Respiration

• Fermentation: Anaerobic process; organic molecule is final electron acceptor; produces acids, alcohols, gases.

• Anaerobic Respiration: Uses electron acceptors other than O2 (e.g., nitrate, sulfate).

• Lipid and Protein Catabolism: Lipids and proteins are broken down for energy when glucose is unavailable.

The Control of Microbial Growth

Mechanisms of Action of Antimicrobial Agents

• Penicillin and Other Antibiotics: Inhibit cell wall synthesis (especially effective against Gram-positive bacteria).

• Lysozyme: Enzyme that breaks down peptidoglycan in bacterial cell walls.

• Alcohol: Denatures proteins and disrupts membranes.

• Detergents: Disrupt cell membranes and denature proteins.

Table: Comparison of Gram-Positive and Gram-Negative Cell Walls

Feature	Gram-Positive	Gram-Negative
Peptidoglycan Layer	Thick	Thin
Teichoic Acids	Present	Absent
Outer Membrane	Absent	Present
Lipopolysaccharide (LPS)	Absent	Present
Sensitivity to Penicillin	High	Low

Example: Scientific Nomenclature

• Example: Staphylococcus aureus (Genus: Staphylococcus, specific epithet: aureus)

Example: ATP Generation Equation

• Substrate-Level Phosphorylation:

$\text{ADP} + \text{P}_i \rightarrow \text{ATP}$

• Oxidative Phosphorylation (Chemiosmosis):

$\text{NADH} + \text{H}^+ + 1/2\ \text{O}_2 \rightarrow \text{NAD}^+ + \text{H}_2\text{O}$

Additional info:

• Some details (e.g., specific steps of the Gram stain, or the full list of microscope parts) were expanded for completeness.

• Table entries and equations were inferred and formatted for clarity.