Microbiology Exam 1 Study Guide: History, Cell Structure, and Metabolism

Introduction to Microbiology

Normal Flora and Pathogens

Normal flora refers to the microorganisms that reside on or within various parts of the human body without causing disease under normal circumstances. Understanding the distinction between normal flora, opportunistic pathogens, and full-time pathogens is essential for recognizing their roles in health and disease.

• Normal Flora: Microbes that are typically harmless and may provide benefits such as preventing colonization by pathogens. However, they can become harmful if they enter sterile areas or if the host's immune system is compromised.

• Opportunistic Pathogens: Microorganisms that cause disease only when the host's defenses are weakened or when they gain access to normally sterile sites.

• Full-Time Pathogens: Microbes that cause disease whenever they are present in the host.

• Types of Symbiosis: Includes mutualism (both benefit), commensalism (one benefits, other unaffected), and parasitism (one benefits, other harmed).

• Examples: Yersinia pestis (Black Plague), Smallpox virus, Influenza virus, HIV (AIDS), Ebola virus, SARS coronavirus.

History of Microbiology

Early Questions and Key Scientists

The field of microbiology began with fundamental questions about the existence and nature of microorganisms. Early scientists made significant contributions to our understanding of microbes and their classification.

• Benefits of Bacteria: Decomposition, nitrogen fixation, food production, biotechnology.

• Detrimental Effects: Disease, food spoilage, bioterrorism.

• Key Questions: (1) Do microbes exist? (2) How are they classified?

• Key Scientists: Hooke (first description of cells), Virchow (cell theory), Schleiden & Schwann (cell theory), Leeuwenhoek (first observation of microbes), Linnaeus (taxonomy).

• Scientific Names: Binomial nomenclature; genus and species, italicized, genus capitalized (e.g., Escherichia coli).

• Classification Levels: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

• Three Domains: Bacteria, Archaea, Eukarya.

• Seven Groups of Microorganisms: Bacteria, Archaea, Fungi, Protozoa, Algae, Viruses, Helminths (cell type, cell wall, reproduction, energy requirements, examples).

Golden Age and Spontaneous Generation Debate

The Golden Age of Microbiology addressed questions about the origin of life, disease causation, and prevention. The Spontaneous Generation Debate was pivotal in establishing the scientific method and understanding microbial life.

• Spontaneous Generation: The belief that life arises spontaneously from non-living matter.

• Key Scientists: Aristotle (supported spontaneous generation), Redi (disproved with meat experiment), Needham (supported with broth experiment), Spallanzani (disproved with sealed flasks), Pasteur (definitively disproved with swan-neck flask experiment).

• Scientific Method Steps: Observation, Hypothesis, Experiment, Analysis, Conclusion.

• Pasteur's Contributions: Fermentation, pasteurization, disproved spontaneous generation, developed vaccines.

• Fermentation: Microbial conversion of sugars to alcohol or acids.

• Pasteurization: Heat treatment to kill pathogens in food and beverages.

• Buchner: Demonstrated enzymes in fermentation.

Germ Theory and Disease Prevention

The Germ Theory of Disease established that microorganisms cause disease. Key scientists contributed to understanding etiology, staining, and infection prevention.

• Pasteur: Industrial microbiology, fermentation.

• Koch: Etiology, Koch's postulates.

• Gram: Developed Gram stain.

• Semmelweis, Lister, Nightingale, Snow: Infection control and epidemiology.

• Jenner: Early immunology, smallpox vaccine.

• Ehrlich, Fleming: Chemotherapeutic agents (antibiotics).

• Antimicrobial Agents: Penicillin (Fleming), Salvarsan (Ehrlich).

Modern Age and Applications

Modern microbiology explores genetics, molecular biology, environmental roles, disease defense, and future directions.

• Key Questions: Chemical reactions of life, gene function, environmental roles, disease defense, future prospects.

• Key Terms: Bacteriology, mycology, virology, parasitology, microbial genetics, molecular biology, genomics, recombinant DNA, gene therapy, biotechnology, bioremediation, EIDS (Emerging Infectious Diseases).

• Woese: Defined domains using ribosomal RNA.

• Biochemistry Applications: Drug development, diagnostics, environmental remediation.

• EIDS and Bioterrorism Agents: Examples include Bacillus anthracis (anthrax), Ebola virus, SARS coronavirus.

Microbes and Diseases

• Streptococcus pyogenes: Germ Theory, infection control.

• Clostridium perfringens: Germ Theory, wound infections.

• Vibrio cholerae: Germ Theory, cholera.

• Bacillus anthracis: Germ Theory, anthrax.

• Cowpox/Smallpox: Immunology, vaccine development.

Prokaryotic Cell Structure & Function

Cell Types and Structures

Cells are classified as prokaryotic or eukaryotic based on structural features. Understanding their differences is fundamental to microbiology.

• Five Major Processes: Growth, reproduction, responsiveness, metabolism, cellular structure.

• Two Basic Types: Prokaryotic (no nucleus), Eukaryotic (nucleus).

• Comparison: Prokaryotes lack membrane-bound organelles; eukaryotes possess them.

Glycocalyces, Capsules, and Slime Layers

Glycocalyces are external structures that protect cells and aid in attachment. Capsules are organized and firmly attached; slime layers are loose and unorganized.

• Composition: Polysaccharides, polypeptides.

• Functions: Protection from desiccation, immune evasion, adherence.

• Clinical Relevance: Capsules increase virulence.

Flagella and Surface Appendages

Flagella, fimbriae, and pili are surface structures involved in motility and attachment.

• Flagella: Motility; structure includes filament, hook, and basal body.

• Endoflagellum (Axial Filament): Found in spirochetes; enables corkscrew movement.

• Fimbriae: Attachment to surfaces.

• Pili: Conjugation (DNA transfer).

Cell Walls and Gram Staining

Prokaryotic cell walls differ in structure and staining properties, affecting clinical outcomes.

• Gram-Positive: Thick peptidoglycan, teichoic acids, stains purple.

• Gram-Negative: Thin peptidoglycan, outer membrane with lipopolysaccharide (LPS), stains pink.

• Clinical Implications: Gram-negative bacteria are more resistant to antibiotics due to the outer membrane.

• Bacteria vs. Archaea: Archaeal cell walls lack peptidoglycan.

Membrane Structure and Transport

The cytoplasmic membrane is a phospholipid bilayer described by the fluid mosaic model. It regulates transport of substances.

• Phospholipid Bilayer: Hydrophilic heads, hydrophobic tails.

• Fluid Mosaic Model: Proteins float in or on the fluid lipid bilayer.

• Functions: Selective permeability, energy generation.

• Passive Transport: Diffusion, facilitated diffusion, osmosis.

• Osmosis and Tonicity: Movement of water; isotonic (equal), hypertonic (water leaves cell), hypotonic (water enters cell).

• Active Transport: Requires energy; types include uniport, antiport, group translocation (unique to bacteria).

• Comparison: Passive does not require energy; active does.

Cytosol and Internal Structures

Prokaryotic and archaeal cytosol contains essential components for cellular function.

• Nucleoid: Region containing DNA.

• Ribosomes: Protein synthesis.

• Endospores: Survival structures.

• Plasmids: Extra-chromosomal DNA.

Cell Shapes and Arrangements

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

• Arrangements: Chains, clusters, pairs.

Eukaryotic Cell Features

Eukaryotic cells have unique structures and processes.

• Glycocalyces: Protection and cell recognition.

• Cell Walls: Found in plants, fungi; composition varies.

• Cytoplasmic Membrane: Similar to prokaryotes.

• Exocytosis/Endocytosis: Bulk transport mechanisms.

• Pseudopodia, Cilia, Flagella: Motility and feeding.

• Organelles: Non-membranous (ribosomes, cytoskeleton, centrioles, centrosomes); membranous (nucleus, ER, Golgi, lysosome, peroxisome, vesicle, vacuole, mitochondrion, chloroplast).

• Endosymbiotic Theory: Mitochondria and chloroplasts originated from prokaryotes.

• Evidence: Double membranes, own DNA, ribosomes similar to prokaryotes.

Microbes and Cell Structures

• Streptococcus: Slime layer.

• Clostridium: Endospores.

• Neisseria gonorrhoeae: Fimbriae.

Metabolism

Metabolic Processes

Metabolism encompasses all chemical reactions in a cell, including energy production and biosynthesis.

• Metabolism: All chemical reactions.

• Anabolism: Building molecules; requires energy.

• Catabolism: Breaking down molecules; releases energy.

• Heterotrophs: Use organic carbon.

• Autotrophs: Use inorganic carbon (CO2).

• Energy Transformation: Conversion of energy forms.

Redox Reactions and ATP

Reduction and oxidation reactions are central to energy transfer. ATP is the universal energy currency.

• Reduction: Gain of electrons.

• Oxidation: Loss of electrons.

• ATP: Adenosine triphosphate; stores and transfers energy.

• ATP Cycle: ATP → ADP + Pi (energy released); ADP + Pi → ATP (energy stored).

ATP Cycle Equation:

$\mathrm{ATP} \rightarrow \mathrm{ADP} + \mathrm{P_i} + \text{energy}$

$\mathrm{ADP} + \mathrm{P_i} + \text{energy} \rightarrow \mathrm{ATP}$

ATP Phosphorylation Types

• Substrate-Level Phosphorylation: Direct transfer of phosphate.

• Oxidative Phosphorylation: Electron transport chain.

• Photophosphorylation: Light-driven.

Enzymes and Their Activity

Enzymes catalyze metabolic reactions. Their activity is influenced by environmental factors.

• Six Types of Enzymes: Oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases.

• Activation Energy: Energy required to start a reaction.

• Active Site: Region where substrate binds.

• Substrate: Molecule acted upon by enzyme.

• Factors Affecting Activity: Temperature, pH, substrate concentration, competitive/noncompetitive inhibition.

Respiration and Fermentation

Cells obtain energy through respiration and fermentation. The stages of respiration are glycolysis, acetyl CoA formation, Krebs cycle, and electron transport chain.

• Glycolysis: Glucose → pyruvate; occurs in cytoplasm.

• Acetyl CoA Formation: Pyruvate → acetyl CoA.

• Krebs Cycle: Acetyl CoA → CO2, NADH, FADH2.

• Electron Transport Chain: NADH, FADH2 donate electrons; ATP produced.

• NADH and FADH2: Electron carriers.

• Aerobic vs. Anaerobic: Aerobic uses O2; anaerobic uses other electron acceptors.

• Fermentation: Anaerobic; produces organic acids, alcohols.

• End Products: Lactic acid, ethanol, CO2.

Photosynthesis

Photosynthesis is the process by which cells convert light energy into chemical energy. It occurs in specialized pigments and organelles.

• Definition: Conversion of light energy to chemical energy.

• Pigment: Chlorophyll.

• Location: Prokaryotes (membranes), eukaryotes (chloroplasts).

• Light-Dependent Reactions: Produce ATP and NADPH.

• Light-Independent Reactions: Use CO2 to produce glucose.

Respiration Equation:

$\mathrm{C_6H_{12}O_6} + 6\mathrm{O_2} \rightarrow 6\mathrm{CO_2} + 6\mathrm{H_2O} + \text{energy}$

Photosynthesis Equation:

$6\mathrm{CO_2} + 6\mathrm{H_2O} + \text{light energy} \rightarrow \mathrm{C_6H_{12}O_6} + 6\mathrm{O_2}$

Summary Table: Comparison of Prokaryotic and Eukaryotic Cells

Feature	Prokaryotic Cells	Eukaryotic Cells
Nucleus	Absent	Present
Membrane-bound Organelles	Absent	Present
Cell Wall	Peptidoglycan (Bacteria), varied (Archaea)	Cellulose (plants), chitin (fungi), absent (animals)
Ribosomes	70S	80S
Reproduction	Binary fission	Mitosis/meiosis
Examples	Bacteria, Archaea	Plants, animals, fungi, protists

Summary Table: Types of Microorganisms

Group	Cell Type	Cell Wall	Reproduction	Energy Requirement	Example
Bacteria	Prokaryotic	Peptidoglycan	Binary fission	Heterotrophic/autotrophic	Escherichia coli
Archaea	Prokaryotic	Varied, no peptidoglycan	Binary fission	Heterotrophic/autotrophic	Halobacterium
Fungi	Eukaryotic	Chitin	Sexual/asexual	Heterotrophic	Aspergillus
Protozoa	Eukaryotic	None	Sexual/asexual	Heterotrophic	Amoeba
Algae	Eukaryotic	Cellulose	Sexual/asexual	Autotrophic	Chlamydomonas
Viruses	Acellular	None	Replication in host	Obligate intracellular	Influenza virus
Helminths	Eukaryotic	None	Sexual/asexual	Heterotrophic	Tapeworm

Additional info: Some explanations and examples were expanded for academic completeness and clarity. Tables were inferred and constructed based on standard microbiology content.