Microbiology Chapters 11–13: Prokaryotes, Eukaryotes, and Viruses Study Guide

Chapter 11: Prokaryotes

Basics of Prokaryotes

Prokaryotes are unicellular organisms lacking a true nucleus and membrane-bound organelles. Their cell structure and physiology are foundational to microbiology.

• Cell Type: Prokaryotic cells have a single, circular chromosome and no nuclear membrane.

• Cell Wall: Most have a rigid cell wall composed of peptidoglycan (bacteria) or pseudopeptidoglycan (archaea).

• Special Structures:

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

  • Flagella: Used for motility; structure differs from eukaryotic flagella.

  • Capsule: Gelatinous outer layer for protection and adherence.

  • Endospores: Highly resistant, dormant structures formed by some bacteria (e.g., Bacillus, Clostridium).

• Reproduction: Mainly by binary fission, a simple form of asexual reproduction.

Gram Staining

Gram staining differentiates bacteria based on cell wall structure:

• Gram Positive: Thick peptidoglycan layer, stains purple (e.g., Staphylococcus, Bacillus).

• Gram Negative: Thin peptidoglycan layer and outer membrane, stains pink (e.g., Escherichia, Salmonella).

Major Bacterial Groups and Features

Key genera and their characteristics:

• Streptococcus: Gram-positive cocci, chains, causes strep throat.

• Pseudomonas: Gram-negative rods, motile, opportunistic pathogens.

• Rickettsia: Obligate intracellular parasites, cause typhus.

• Bacteroides: Anaerobic, abundant in gut flora.

• Salmonella: Gram-negative rods, cause foodborne illness.

• Escherichia: Includes E. coli, common gut bacterium.

• Staphylococcus: Gram-positive cocci, clusters, cause skin infections.

• Neisseria: Gram-negative diplococci, cause gonorrhea and meningitis.

• Streptomyces: Filamentous, produce antibiotics.

• Spirochetes: Spiral-shaped, motile via axial filaments (e.g., Treponema).

• Wolbachia: Intracellular symbionts of insects.

• Yersinia: Includes Y. pestis, cause of plague.

• Bacillus: Gram-positive rods, form endospores.

• Clostridium: Anaerobic, endospore-forming, cause tetanus, botulism.

• Cyanobacteria: Photosynthetic, oxygen-producing bacteria.

Archaea

Archaea are prokaryotes distinct from bacteria, often found in extreme environments.

• Methanogens: Produce methane, live in anaerobic environments.

• Halophiles: Thrive in high-salt environments.

• Thermophiles: Live in high-temperature environments.

Bacterial Shapes and Arrangements

• Cocci: Spherical (single, chains, clusters).

• Bacilli: Rod-shaped (single, chains).

• Spirilla/Spirochetes: Spiral-shaped.

Bacterial Motility

• Flagella (most common), axial filaments (spirochetes), gliding, or twitching motility.

Chapter 12: Eukaryotes (Protists, Fungi, and Animals)

Defining Eukaryotic Cells

Eukaryotic cells have a true nucleus and membrane-bound organelles, distinguishing them from prokaryotes.

• Nucleus: Contains genetic material.

• Organelles: Mitochondria, endoplasmic reticulum, Golgi apparatus, etc.

Protists

Protists are a diverse group of eukaryotic microorganisms. Some are pathogenic, others have unique features.

• Giardia: Causes giardiasis, a diarrheal disease.

• Dinoflagellates: Some produce toxins causing red tides.

• Trypanosoma: Causes sleeping sickness (transmitted by tsetse fly).

• Amoeba: Includes Entamoeba histolytica, causes amoebic dysentery.

• Euglena: Photosynthetic, has flagellum.

• Phytophthora: Plant pathogen, causes potato blight.

• Plasmodium: Causes malaria (transmitted by Anopheles mosquito).

• Brown, Green, Red Algae: Photosynthetic, important in aquatic ecosystems.

Disease Vectors

• Vector: An organism that transmits pathogens (e.g., mosquitoes, ticks, flies).

• Examples:

  • Anopheles mosquito: Malaria

  • Tsetse fly: Sleeping sickness

  • Ticks: Lyme disease

Helminths (Tapeworms, Ringworms, Roundworms)

• Tapeworms: Flat, segmented, intestinal parasites.

• Ringworms: Fungal infection, not a worm.

• Roundworms: Cylindrical, unsegmented, cause diseases like ascariasis.

Fungi

• Cell Wall: Composed of chitin.

• Hyphae: Filamentous structures forming the mycelium.

• Mycelium: Mass of hyphae, main body of fungus.

• Reproduction: Sexual and asexual spores.

Chapter 13: Viruses, Viroids, and Prions

Definitions

• Virus: Acellular infectious agent with DNA or RNA, protein coat (capsid), sometimes an envelope.

• Viroid: Infectious RNA molecule, no protein coat, affects plants.

• Prion: Infectious protein, causes neurodegenerative diseases.

Structure of Viruses

• Capsid: Protein shell enclosing nucleic acid.

• Envelope: Lipid membrane derived from host cell (in enveloped viruses).

• Spikes: Glycoproteins for attachment.

Viral Infection and Reproduction

• Lytic Cycle: Virus replicates, lyses host cell.

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

Enveloped Viruses

• Have a lipid envelope, often more sensitive to environmental conditions.

• Enter host cells via membrane fusion or endocytosis.

Latent Viruses

• Remain dormant in host cells, can reactivate (e.g., herpesviruses).

Types of Viruses

• RNA Viruses: Influenza, HIV, West Nile, COVID-19.

• DNA Viruses: Hepatitis B, Herpesviruses, Smallpox.

• Retroviruses: HIV (reverse transcription of RNA to DNA).

Viruses and Cancer

• Some viruses can activate oncogenes, leading to cancer (e.g., HPV and cervical cancer).

Key Terms

• Emerging: Newly identified or increasing in incidence.

• Epidemic: Sudden increase in disease cases in a region.

• Pandemic: Worldwide epidemic.

• Pathogen: Disease-causing organism.

• Vector: Organism transmitting a pathogen.

• Reservoir: Natural host or habitat of a pathogen.

Examples of Viral Diseases

• Flu (Influenza): RNA virus, respiratory illness.

• Polio: RNA virus, affects nervous system.

• Hepatitis: Several types (A, B, C), affect liver.

• Ebola: RNA virus, causes hemorrhagic fever.

• Colds: Many viruses, mainly rhinoviruses.

• HIV and AIDS: Retrovirus, attacks immune system.

• West Nile: RNA virus, mosquito-borne.

• COVID-19: Caused by SARS-CoV-2, RNA virus.

• Spanish Flu (H1N1): Historic influenza pandemic.