Comprehensive Study Notes for Microbiology Final Exam (Biology 221)

Introduction to the Microbial World

The Three Domains of Life

The three domains—Bacteria, Archaea, and Eukarya—represent the highest level of biological classification. Each domain is unique in its cellular structure, genetic makeup, and ecological roles.

• Bacteria: Prokaryotic, peptidoglycan cell walls, diverse metabolic pathways.

• Archaea: Prokaryotic, cell walls lack peptidoglycan, often extremophiles (e.g., thermophiles, halophiles).

• Eukarya: Eukaryotic cells, includes fungi, protozoa, algae, plants, and animals.

Levels of Biological Classification: Domain > Kingdom > Phylum > Class > Order > Family > Genus > Species

Unique Features of Major Microbial Groups:

• Algae: Photosynthetic eukaryotes, important for oxygen production.

• Viruses: Acellular, require host cells for replication, contain DNA or RNA.

• Protozoa: Unicellular eukaryotes, often motile, diverse life cycles.

• Fungi: Eukaryotic, cell walls of chitin, includes yeasts and molds.

• Bacteria: Prokaryotic, diverse morphologies and metabolisms.

• Archaea: Prokaryotic, unique membrane lipids, often inhabit extreme environments.

Cell Structure and Function

Bacterial Morphology

Bacteria exhibit various shapes, including cocci (spherical), bacilli (rod-shaped), spirilla (spiral), and others. Morphology affects motility, nutrient uptake, and pathogenicity.

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic Cells: Lack a nucleus, have circular DNA, no membrane-bound organelles.

• Eukaryotic Cells: Have a nucleus, linear DNA, and membrane-bound organelles (e.g., mitochondria, ER).

Gram-Positive vs. Gram-Negative Bacteria

• Gram-Positive: Thick peptidoglycan layer, teichoic acids, stain purple in Gram stain.

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

Functional Differences: Gram-negative bacteria are generally more resistant to antibiotics due to their outer membrane.

Microbial Metabolism

Glycolysis Overview

Glycolysis is the metabolic pathway that converts glucose into pyruvate, generating ATP and NADH.

• Equation: $\text{Glucose} + 2\,\text{NAD}^+ + 2\,\text{ADP} + 2\,\text{P}_i \rightarrow 2\,\text{Pyruvate} + 2\,\text{NADH} + 2\,\text{ATP} + 2\,\text{H}_2\text{O}$

Respiration vs. Fermentation

• Respiration: Requires oxygen (aerobic) or other electron acceptors (anaerobic), produces more ATP, end products include CO2 and H2O.

• Fermentation: Occurs without oxygen, less ATP produced, end products include lactic acid, ethanol, or other organic acids.

Energy Sources

• Chemoheterotrophs: Obtain energy and carbon from organic compounds (e.g., most bacteria, animals).

• Photoautotrophs: Use light as energy source and CO2 as carbon source (e.g., cyanobacteria, algae).

Microbial Growth

Cardinal Temperatures

Each microorganism has minimum, optimum, and maximum growth temperatures.

• Psychrophiles: Grow best at low temperatures (0–20°C).

• Mesophiles: Grow best at moderate temperatures (20–45°C).

• Thermophiles: Grow best at high temperatures (45–80°C).

Biofilms

Biofilms are communities of microorganisms attached to surfaces, embedded in a self-produced matrix. They are important in medical and environmental contexts due to increased resistance to antimicrobials.

Oxygen Requirements

• Obligate Aerobes: Require oxygen for growth.

• Facultative Anaerobes: Can grow with or without oxygen.

• Obligate Anaerobes: Cannot tolerate oxygen.

• Microaerophiles: Require low levels of oxygen.

Bacterial Growth

Bacterial growth is typically measured by increase in cell number, following a characteristic growth curve: lag, log (exponential), stationary, and death phases.

Control of Microbial Growth

Physical and Chemical Methods

Various methods are used to control microbial growth, including heat (autoclaving, pasteurization), filtration, radiation, and chemical agents (disinfectants, antiseptics).

• Physical Methods: Heat, filtration, radiation.

• Chemical Methods: Alcohols, halogens, phenolics, quaternary ammonium compounds.

Effectiveness depends on: Type of microbe, concentration of agent, exposure time, and presence of organic matter.

Microbial Genetics

Structure of DNA and RNA

• DNA: Double helix, deoxyribose sugar, bases A-T and G-C.

• RNA: Single-stranded, ribose sugar, bases A-U and G-C.

Bacterial vs. Human DNA

• Bacterial DNA: Usually circular, single chromosome, may have plasmids.

• Human DNA: Linear, multiple chromosomes, no plasmids.

Enzymes in DNA Replication

• DNA Polymerase: Synthesizes new DNA strands.

• Helicase: Unwinds DNA helix.

• Ligase: Joins DNA fragments.

Transcription and Translation

• Transcription: DNA is transcribed to mRNA.

• Translation: mRNA is translated into protein.

• Differences: In prokaryotes, transcription and translation are coupled; in eukaryotes, they are separated by the nuclear envelope.

Plasmids and Genetic Transfer

• Plasmids: Small, circular DNA molecules in bacteria, often carry antibiotic resistance genes.

• Genetic Transfer: Transformation, transduction, and conjugation are main mechanisms.

Biotechnology and DNA Technology

Tools of Biotechnology

• Restriction Enzymes: Cut DNA at specific sequences.

• Vectors: Plasmids or viruses used to transfer genes.

• PCR (Polymerase Chain Reaction): Amplifies DNA sequences.

Recent Advances: CRISPR-Cas9 gene editing, next-generation sequencing.

Classification of Microorganisms

Microbial Diversity

Classification is based on genetic, morphological, and metabolic characteristics. Key groups include bacteria, archaea, fungi, protozoa, algae, and viruses.

The Eukaryotes: Fungi, Algae, Protozoa, and Helminths

Key Microbes

• Protozoa: Giardia lamblia, Plasmodium spp. (malaria), Trypanosoma spp.

• Fungi: Candida albicans, Aspergillus spp.

• Algae: Chlamydomonas, Volvox

Viruses, Viroids, and Prions

Viral Structure and Function

• Components: Nucleic acid (DNA or RNA), capsid, sometimes envelope.

• Comparison: Viruses are acellular, unlike bacteria and human cells.

Viral Life Cycles

• Lytic Cycle: Virus replicates and lyses host cell.

• Lysogenic Cycle: Viral DNA integrates into host genome, replicates with host.

• Animal Virus Multiplication: Attachment, entry, uncoating, replication, assembly, release.

Microbial Mechanisms of Pathogenicity

Portals of Entry and Transmission

• Portals of Entry: Mucous membranes, skin, parenteral route.

• Transmission: Direct contact, airborne, vector-borne, etc.

Virulence Factors

• Structures: Capsules, fimbriae, enzymes, toxins.

• Endotoxins: Part of Gram-negative cell wall (LPS), cause fever and shock.

• Exotoxins: Secreted proteins, specific effects (e.g., neurotoxins, enterotoxins).

Innate Immunity: Nonspecific Defenses

First Line of Defense

• Physical Barriers: Skin, mucous membranes.

• Chemical Factors: Lysozyme, acidic pH, antimicrobial peptides.

Second Line of Defense

• Cells: Neutrophils, macrophages, dendritic cells, natural killer cells.

• Inflammation: Redness, heat, swelling, pain; recruits immune cells to infection site.

• Phagocytosis: Engulfment and destruction of microbes.

Complement System

• Pathways: Classical, alternative, lectin.

• Outcomes: Opsonization, inflammation, cell lysis.

Adaptive Immunity: Specific Defenses

Cells of the Third Line of Defense

• B Cells: Originate and mature in bone marrow; produce antibodies.

• T Cells: Originate in bone marrow, mature in thymus; include helper, cytotoxic, and regulatory T cells.

Antibodies

• Structure: Y-shaped proteins with variable and constant regions.

• Classes: IgG, IgM, IgA, IgE, IgD.

• Functions: Neutralization, opsonization, complement activation.

Antigen Presenting Cells (APCs)

• Types: Dendritic cells, macrophages, B cells.

• Function: Present antigens to T cells to initiate adaptive response.

Types of Adaptive Immunity

• Active: Natural (infection), artificial (vaccination).

• Passive: Natural (maternal antibodies), artificial (antibody therapy).

Practical Applications of Immunology

Vaccinations

• Types: Live attenuated, inactivated, subunit, toxoid, conjugate, mRNA vaccines.

• Strengths/Weaknesses: Live vaccines provide strong, long-lasting immunity but may not be safe for immunocompromised individuals.

Diagnostic Tests

• Sensitivity/Specificity: Measures of test accuracy.

• Monoclonal Antibodies: Used in diagnostics and therapy.

• Agglutination Reactions: Detect antigen-antibody interactions.

• ELISA: Enzyme-linked immunosorbent assay for detecting antigens or antibodies.

Disorders Associated with the Immune System

Hypersensitivities

• Type I: Immediate (allergies, anaphylaxis).

• Type II: Cytotoxic (hemolytic anemia).

• Type III: Immune complex (serum sickness).

• Type IV: Delayed-type (contact dermatitis).

Autoimmune Diseases

Diseases where the immune system attacks self-tissues (e.g., lupus, rheumatoid arthritis).

Transplantation Immunology

Immune responses can lead to graft rejection; immunosuppressive therapy is often required.

HIV/AIDS

HIV infects CD4+ T cells, leading to immunodeficiency and increased susceptibility to infections.

Antimicrobial Drugs

Mechanisms of Action

• Inhibit cell wall synthesis (e.g., penicillins).

• Inhibit protein synthesis (e.g., tetracyclines).

• Inhibit nucleic acid synthesis (e.g., quinolones).

• Disrupt cell membrane function (e.g., polymyxins).

Summary Table: Oxygen Requirements of Microorganisms

Type	Oxygen Requirement	Growth Pattern in Thioglycollate Broth
Obligate Aerobe	Requires O2	Growth at top only
Facultative Anaerobe	Grows with or without O2	Growth throughout, more at top
Obligate Anaerobe	Cannot tolerate O2	Growth at bottom only
Microaerophile	Requires low O2	Growth just below surface

Additional info:

• For chapters 21-26, focus on the learning objectives and microbe sets as recommended by your instructor.

• Review laboratory-reinforced protozoan examples for Chapter 12.