Microbiology Study Guide: History, Cell Structure, Microbial Growth, Prokaryote Classification, and Viruses

Chapt 1 – A Brief History of Microbiology

Key Vocabulary and Concepts

• Prokaryote vs Eukaryote: Prokaryotes are organisms without a true nucleus or membrane-bound organelles ("before nucleus"). Eukaryotes have a true nucleus and membrane-bound organelles ("true nucleus").

• Pathogen: A microorganism capable of causing disease.

• Bioterrorism: The use of microorganisms or toxins to intentionally cause disease or death in humans, animals, or plants for terrorist purposes.

• Microbiome: The collection of all microorganisms living in association with the human body or another environment.

• Taxonomy: The science of classifying organisms.

• Protozoa vs Protist: Protozoa are single-celled eukaryotes, often motile and heterotrophic. Protists is a broader group including protozoa, algae, and some fungi-like organisms.

• Viruses: Acellular infectious agents composed of nucleic acid (DNA or RNA) and a protein coat; some have an envelope.

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

  • suspected causative agent must be found in every disease case

  • agent must be isolated and grown outside host

  • when agent introduced to healthy susceptible host, host must acquire disease

  • same agent must be found in diseased experimental host

• Fungi (Yeast vs Molds): Yeasts are unicellular fungi; molds are multicellular, filamentous fungi.

• Germ Theory of Disease: The concept that specific diseases are caused by specific microorganisms (pathogens).

• Archaea: Prokaryotes with unique cell wall polymers, often found in extreme environments; many are chemotrophs.

• Vaccinations: The process of conferring immunity by inoculation with avirulent or killed pathogens.

• Biogenesis: The principle that living cells arise only from preexisting living cells.

• Spontaneous Generation: The disproven idea that living organisms can arise from nonliving matter.

Historical Figures and Discoveries

• Antonie van Leeuwenhoek: Used a simple microscope to observe microorganisms, grouping them into six categories: bacteria, archaea, fungi, protozoa, algae, and small multicellular animals (later, viruses and prions were added).

• Robert Hooke: Coined the term "cell" after observing cork; contributed to the development of cell theory.

• Golden Age of Microbiology: Scientists like Bassi and Pasteur demonstrated the link between microorganisms and disease, leading to the invention of disinfectants and the development of the germ theory.

• Pasteur: Demonstrated the role of bacteria in fermentation and spoilage, leading to pasteurization.

Classification of Microorganisms

• Fungi: Eukaryotic, may have cell walls, includes molds and yeasts.

• Protozoa: Single-celled eukaryotes, obtain nourishment by absorption or ingestion.

• Algae: Photosynthetic eukaryotes.

• Bacteria and Archaea: Prokaryotic, unicellular, asexual reproduction (binary fission), ubiquitous, can survive extreme environments.

• Viruses: Acellular, require host cells for replication.

• Animalia: Multicellular parasites (e.g., helminths).

Key Theories

• Biogenesis vs Spontaneous Generation: Biogenesis states that life arises from preexisting life; spontaneous generation (now disproven) claimed life could arise from nonliving matter.

Chapt 3 – Cell Structure and Function

Prokaryote vs Eukaryote

• Prokaryotes: No membrane-bound organelles, DNA in nucleoid, cell wall (peptidoglycan in bacteria), divide by binary fission.

• Eukaryotes: Membrane-bound organelles, DNA in nucleus, cell wall (if present, e.g., in plants/fungi), divide by mitosis/meiosis.

Cell Morphology

• Size, shape, and arrangement of cells are important for identification.

  • Cocci vs bacilli vs spiral

Prokaryotic Cell Structures

• External Structures:

  • Glycocalyx: Gelatinous outer layer for protection and attachment.

  • Flagella: Motility structures.

  • Axial Filaments: Motility in spirochetes.

  • Fimbriae: Attachment to surfaces.

  • Pili: DNA transfer (conjugation).

• Cell Wall:

  • Gram-positive: Thick peptidoglycan layer.

  • Gram-negative: Thin peptidoglycan, outer membrane.

• Gram Stain: Differential stain to distinguish Gram-positive and Gram-negative bacteria.

• Plasma Membrane: Fluid mosaic model; controls transport.

  • Passive Transport: Simple diffusion, facilitated diffusion, osmosis.

  • Active Transport: Requires energy (e.g., group translocation).

  • ISO vs HYPER vs HYPO

    • Isotonic: no net movement of water

    • Hyper: cell shrinks (water out of cell)

    • Hypo: cell expands (water into cell)

• Internal Structures:

  • Nucleoid: Region containing DNA.

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

  • Inclusions: Storage granules - reserve deposits of lipids/starch

  • Endospores: Resistant structures for survival.

Eukaryotic Cell Structures

• Flagella and Cilia: Motility structures (9+2 microtubule arrangement).

• Cell Wall: Present in plants, fungi, algae (composition varies).

• Glycocalyx: Outer layer for protection and cell recognition.

• Plasma Membrane: Similar to prokaryotes; endocytosis and exocytosis for transport.

  • endo: physical manipulation of cyto membrane around cytoskeleton

    • phagocytosis: pulls SOLID in cell

    • pinocytosis: pull LIQUID in cell

  • exo: substance export out of cell (waste/secretions)

• Cytoplasm and Cytoskeleton: Support and shape.

• Ribosomes: 80S in eukaryotes (except 70S in mitochondria/chloroplasts).

• Membranous Organelles: Nucleus, endoplasmic reticulum, Golgi complex, mitochondria, chloroplasts, vacuoles, lysosomes, centrosomes.

Endosymbiotic Theory

• Explains origin of mitochondria and chloroplasts as formerly free-living prokaryotes engulfed by ancestral eukaryotic cells.

Processes of Life

• Growth, reproduction, responsiveness, metabolism.

Chapt 6 – Microbial Nutrition and Growth

Microbial Nutrition Types

• Chemoheterotroph: Obtain energy and carbon from organic compounds.

• Photoautotroph: Use light for energy and CO2 as carbon source.

Temperature Preferences

• Mesophile: Moderate temperature-loving (20–45°C).

• Psychrophile: Cold-loving (<15°C).

• Thermophile: Heat-loving (45–80°C).

• Hyperthermophile: Extreme heat-loving (>80°C).

Microbial Growth Curve

• Lag Phase: Adjustment to environment, little cell division.

• Log (Exponential) Phase: Rapid cell division, population doubles at constant rate.

• Stationary Phase: Rate of cell growth equals rate of cell death.

• Death Phase: Cells die faster than new cells are produced.

Oxygen Requirements

• Aerobe: Requires oxygen.

• Anaerobe: Cannot tolerate oxygen.

• Catalase: Enzyme that breaks down hydrogen peroxide; used to distinguish between certain bacteria.

Essential Elements

• Carbon, hydrogen, oxygen, nitrogen, and trace elements are required for microbial growth.

Other Key Concepts

• Endospores: Dormant, resistant structures formed by some bacteria.

• Biofilm: Community of microorganisms attached to a surface.

• Nitrogen Fixation: Conversion of atmospheric nitrogen to ammonia by certain bacteria.

Chapt 11 – Characterizing and Classifying Prokaryotes

Prokaryotic Reproduction and Morphology

• Binary Fission: Most common method of prokaryotic reproduction.

• Budding: Alternative method in some bacteria.

• Morphologies: Cocci (spherical), bacilli (rod-shaped), coccobacilli, vibrios (comma-shaped), spirals.

• Arrangements: Single, diplo (pairs), staphylo (clusters), tetrad (groups of four), sarcina (cubes), palisade (side-by-side rods).

Prokaryotic Characteristics

• Extremophiles: Thrive in extreme environments.

• Motility: Flagella, axial filaments, gliding.

• Ubiquitous: Found everywhere.

• Fomite: Inanimate object that can transmit pathogens.

• Hemolysis: Lysis of red blood cells, used in bacterial identification.

• Chemotroph: Obtain energy from chemicals.

• Phototroph: Obtain energy from light.

• Endotoxin vs Exotoxin: Endotoxins are part of Gram-negative cell walls (lipopolysaccharide); exotoxins are secreted proteins, often by Gram-positive bacteria.

Classification and Domains

• Three Domains: Bacteria, Archaea, Eukarya.

• Gram-positive vs Gram-negative: Based on cell wall structure and Gram stain reaction.

• Modern Prokaryote Classification: Based on genetic, biochemical, and phenotypic characteristics.

Human Pathogens

• Clostridium and Bacillus: Cause diseases such as botulism, tetanus, anthrax.

• Species of Human Pathogens: Numerous, classified by genus and species.

Chapt 13 – Characterizing and Classifying Viruses, Viroids, and Prions

General Characteristics of Viruses

• Acellular: Not composed of cells; lack characteristics of life outside host.

• Obligate Intracellular Parasites: Require host cell machinery for replication.

• Structure: Nucleic acid (DNA or RNA), protein coat (capsid), some have envelope and spikes.

• Host Range: Determined by specific attachment sites and cellular factors.

• Size: Much smaller than bacteria (measured in nanometers).

Viral Structure

• Virion: Complete, infectious viral particle.

• Capsid: Protein coat made of capsomeres; provides protection and attachment.

• Envelope: Lipid membrane surrounding some viruses.

• Spikes: Glycoproteins for attachment.

• Shapes: Polyhedral (spherical), helical (rod-like), enveloped, complex.

Viral Taxonomy

• Family names end in -viridae; genus names end in -virus.

• Species share genetic information and ecological niche; subspecies designated by numbers.

Viral Cultivation and Identification

• Viruses must be grown in living cells (bacterial lawns, cell cultures, embryonated eggs).

• Bacteriophages form plaques on bacterial lawns.

• Animal and plant viruses grown in cell cultures; continuous cell lines can be maintained indefinitely.

• Serological tests used for identification.

Viral Multiplication Cycles

• Lytic Cycle (Bacteriophages):

  1. Attachment: Phage attaches to host cell.

  2. Entry: Phage injects DNA into cell thru lysosome (peptidoglycan)

  3. Synthesis: Phage DNA and proteins produced (use DNA or RNA) - reproduced the virus

     1. Get rid of og cell DNA and put in viral DNA

  4. Assembly: Phage makes more viral cells - actively producing more:

  5. Release: Phage lysosome break/blows up, cell lysis(dies), releasing new phages.

• Lysogenic Cycle (Temperate Phages):

  1. Attachment

  2. Entry

  3. Prophage in chromosome: fusing DNA and virus - hijacking cell (cause misreads)

  4. Replication of chromosomes: replication of infected cells - daughter cells infected w/ nearly inactive virus (virus always gonna be there)

  5. Induction: process of virus being woken up (anything damage DNA - causes to get out)

  6. Synthesis

  7. Assembly

  8. Release - slow burst

• Multiplication of Animal Viruses:

  1. Attachment: Virus binds to cell membrane.

  2. Penetration: By endocytosis or fusion.

  3. Uncoating: Viral genome released.

  4. Biosynthesis: Viral nucleic acids and proteins produced.

  5. Maturation: Assembly of virions.

  6. Release: By budding (enveloped) or rupture (non-enveloped).

Types of Viral Genomes

• DNA Viruses: Single- or double-stranded; may be enveloped or non-enveloped.

• RNA Viruses: Sense (+) strand, antisense (–) strand, or double-stranded.

• Retroviruses: Single-stranded RNA, use reverse transcriptase to make DNA (e.g., HIV).

Latent and Persistent Infections

• Latent: Virus remains dormant in host cell (e.g., herpesviruses).

• Persistent: Slow, continuous release of virus, often fatal (e.g., measles).

Prions

• Prions: Infectious proteins causing neurodegenerative diseases; transmissible by ingestion, transplant, or surgical instruments.

Plant Viruses and Viroids

• Plant Viruses: Enter through wounds or insect vectors.

• Viroids: Infectious RNA molecules.

Viruses and Cancer

• Some viruses activate oncogenes, transforming normal cells into cancerous cells (loss of contact inhibition, tumor antigens).

• Oncogenic DNA Viruses: Adenoviridae, Herpesviridae, Poxviridae, Papovaviridae, Hepadnaviridae.

Selected DNA Virus Families and Diseases

Family	Genome	Envelope	Example Diseases
Parvoviridae	ssDNA	No	Fifth disease, anemia
Herpesviridae	dsDNA	Yes	Herpes, Kaposi's sarcoma
Poxviridae	dsDNA	Yes	Smallpox, cowpox, molluscum contagiosum
Papovaviridae	dsDNA	No	Warts, tumors
Hepadnaviridae	dsDNA	Yes	Hepatitis B

Summary Table: Virus Structure Types

Type	Capsid Shape	Envelope	Example
Polyhedral	Icosahedral	+/-	Adenovirus
Helical	Rod-like	+/-	Tobacco mosaic virus
Complex	Multiple	No	Bacteriophage