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

Chapter 11 – The Prokaryotes: Domains Bacteria and Archaea

Basics of Prokaryotes

Prokaryotes are unicellular organisms lacking a membrane-bound nucleus and organelles. They include bacteria and archaea, which are distinguished by their cell wall composition, genetic makeup, and environmental adaptations.

• Cell Type: Prokaryotic cells lack a true nucleus; their DNA is located in a nucleoid region.

• Cell Wall: Most bacteria have a cell wall composed of peptidoglycan; archaea have cell walls made of pseudopeptidoglycan or other polymers.

• Special Structures: Many prokaryotes possess pili (for attachment and conjugation), flagella (for movement), capsules (for protection), and endospores (for survival in harsh conditions).

• Reproduction: Prokaryotes reproduce asexually by binary fission.

Gram Staining

Gram staining differentiates bacteria based on cell wall structure:

• Gram-Positive Bacteria: Thick peptidoglycan layer; stain purple.

• Gram-Negative Bacteria: Thin peptidoglycan layer and outer membrane; stain pink/red.

Major Bacterial Groups and Their Features

Key genera and their characteristics:

• Streptococcus: Gram-positive cocci; can cause strep throat, pneumonia.

• Pseudomonas: Gram-negative rods; opportunistic pathogens, resistant to antibiotics.

• Rickettsia: Obligate intracellular parasites; cause typhus, Rocky Mountain spotted fever.

• Bacteroides: Gram-negative anaerobes; common in gut flora.

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

• Escherichia (E. coli): Gram-negative rods; normal flora and some pathogenic strains.

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

• Neisseria: Gram-negative cocci; cause gonorrhea, meningitis.

• Streptomyces: Gram-positive; produce antibiotics.

• Spirochetes: Spiral-shaped; include Treponema (syphilis), Borrelia (Lyme disease).

• Wolbachia: Intracellular symbionts of insects.

• Yersinia: Gram-negative rods; cause plague.

• Bacillus: Gram-positive rods; form endospores, e.g., B. anthracis.

• Clostridium: Gram-positive rods; anaerobic, form endospores, cause tetanus, botulism.

• Cyanobacteria: Photosynthetic bacteria; produce oxygen.

Archaea: Types and Environments

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

• Methanogens: Produce methane; live in anaerobic environments (e.g., swamps).

• Extreme Halophiles: Thrive in high-salt environments (e.g., salt lakes).

• Extreme Thermophiles: Live in very hot environments (e.g., hot springs).

Bacterial Shapes and Arrangements

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

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

• Spirilla/Spirochetes: Spiral-shaped.

Bacterial Motility

• Movement via flagella, axial filaments (spirochetes), gliding, or twitching (pili).

Chapter 12 – The Eukaryotes: Fungi, Algae, Protozoa, and Helminths

Defining Eukaryotic Cells

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

• Examples: Protists, fungi, plants, animals.

Protists: Disease-Causing and Unique Features

• Giardia: Causes giardiasis (intestinal infection).

• Dinoflagellates: Some produce toxins causing red tides.

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

• Amoeba: Includes Entamoeba histolytica (amoebic dysentery).

• Euglena: Photosynthetic, flagellated protist.

• Phytophthora: Plant pathogen (potato blight).

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

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

Common Disease Vectors

• Mosquitoes: Transmit malaria, West Nile virus, yellow fever.

• Tsetse flies: Transmit trypanosomiasis.

• Ticks: Transmit Lyme disease, Rocky Mountain spotted fever.

Helminths: Tapeworms, Ringworms, Roundworms

• Tapeworms: Parasitic flatworms; infect intestines.

• Ringworm: Fungal infection of skin (not a worm).

• Roundworms: Nematodes; cause diseases like ascariasis, trichinosis.

Fungi: Structure and Reproduction

• Cell Wall: Composed of chitin.

• Hyphae: Filamentous structures; collectively form a mycelium.

• 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; infects plants.

• Prion: Infectious protein; causes neurodegenerative diseases.

Structure of Viruses

• Capsid: Protein shell enclosing nucleic acid.

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

• Spikes: Glycoproteins for attachment to host cells.

Viral Infection and Reproduction

• Lytic Cycle: Virus replicates and lyses host cell.

• Lysogenic Cycle: Viral DNA integrates into host genome (prophage); can later enter lytic cycle.

Enveloped Viruses

• Have a lipid envelope; enter host cells by membrane fusion or endocytosis.

Latent Viruses

• Remain dormant in host; can reactivate (e.g., herpes simplex, varicella-zoster).

Types of Viruses

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

• DNA Viruses: Hepatitis B, herpesviruses, smallpox.

• Retroviruses: HIV (reverse transcriptase enzyme).

Viruses and Cancer

• Some viruses can activate oncogenes or disrupt tumor suppressor genes, leading to cancer (e.g., HPV, hepatitis B and C).

Key Terms

• Emerging: Newly identified or increasing in incidence.

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

• Pandemic: Global outbreak of disease.

• Pathogen: Disease-causing organism.

• Vector: Organism transmitting pathogens (e.g., mosquito).

• Reservoir: Natural host or environment where pathogen lives.

Examples of Viral Diseases

• Flu (Influenza): RNA virus; causes respiratory illness.

• Polio: RNA virus; affects nervous system.

• Hepatitis: DNA (B) or RNA (A, C, D, E) viruses; cause liver inflammation.

• Ebola: RNA virus; causes hemorrhagic fever.

• Colds: Usually caused by rhinoviruses (RNA).

• HIV and AIDS: Retrovirus; attacks immune system.

• West Nile: RNA virus; transmitted by mosquitoes.

• COVID-19: RNA coronavirus; causes respiratory illness.

• Spanish Flu (H1N1): RNA influenza virus; caused 1918 pandemic.