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

Chapter 11: Prokaryotes

Overview of Prokaryotes

Prokaryotes are unicellular organisms lacking a true nucleus and membrane-bound organelles. They include bacteria and archaea, which are distinguished by their cellular structures and habitats.

• Cell Type: Prokaryotic cells have a simple structure without a nucleus; genetic material is found in the nucleoid region.

• Cell Walls: Most prokaryotes have cell walls composed of peptidoglycan (bacteria) or pseudopeptidoglycan (archaea).

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

• Reproduction: Prokaryotes reproduce asexually, primarily 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 Genera and Their Features

Key genera to know, with unique features, movement, grouping, and associated diseases or benefits:

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

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

• 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 in clusters; causes skin infections.

• Neisseria: Gram-negative diplococci; causes gonorrhea, meningitis.

• Streptomyces: Gram-positive; produce antibiotics.

• Spirochetes: Spiral-shaped; move by axial filaments; cause Lyme disease, syphilis.

• Wolbachia: Intracellular symbionts of insects.

• Yersinia: Gram-negative rods; cause plague.

• Bacillus: Gram-positive rods; form endospores; B. anthracis causes anthrax.

• 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).

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

• Thermophiles: Live in high-temperature environments (e.g., hot springs).

Bacterial Shapes and Arrangements

• Cocci: Spherical; found singly, in chains (strepto-), or clusters (staphylo-).

• Bacilli: Rod-shaped; can be single, in pairs (diplo-), or chains.

• Spirilla/Spirochetes: Spiral-shaped; flexible or rigid.

Bacterial Motility

• Flagella: Most common structure for movement.

• Axial Filaments: Used by spirochetes for corkscrew motion.

• Gliding and Twitching: Some bacteria move without flagella, using surface proteins or pili.

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

Defining Eukaryotic Cells

Eukaryotic cells have a true nucleus and membrane-bound organelles, distinguishing them from prokaryotes. Their DNA is linear and enclosed within a nuclear envelope.

Protists: Disease-Causing and Unique Features

• Giardia: Causes giardiasis (intestinal infection); flagellated protozoan.

• Dinoflagellates: Some produce toxins causing red tides; photosynthetic.

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

• Amoeba: Move by pseudopodia; some cause amoebic dysentery.

• Euglena: Photosynthetic and motile; has both plant and animal features.

• Phytophthora: Water mold; causes plant diseases like late blight in potatoes.

• Plasmodium: Causes malaria; transmitted by Anopheles mosquitoes.

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

Common Disease Vectors

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

• Tsetse Flies: Transmit Trypanosoma (sleeping sickness).

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

Helminths: Tapeworms, Ringworms, Roundworms

• Tapeworms (Cestodes): Intestinal parasites; absorb nutrients through skin.

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

• Roundworms (Nematodes): Intestinal and tissue parasites; e.g., Ascaris, hookworm.

Fungi: Structure and Reproduction

• Cell Wall Composition: Made of chitin.

• Hyphae: Thread-like filaments forming the body of fungi.

• Mycelium: Mass of hyphae; main vegetative structure.

• Reproduction: Both sexual and asexual spores.

Chapter 13: Viruses, Viroids, and Prions

Definitions

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

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

• Prion: Infectious protein; causes neurodegenerative diseases.

Structure of Viruses

• Nucleic Acid: DNA or RNA (not both).

• Capsid: Protein coat surrounding nucleic acid.

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

• Spikes: Glycoproteins for attachment to host cells.

Viral Infection and Reproduction

• Attachment: Virus binds to host cell.

• Penetration: Entry of viral genome into host.

• Biosynthesis: Host machinery makes viral components.

• Maturation: Assembly of new virions.

• Release: New viruses exit host cell.

Lytic vs. Lysogenic Cycles

• Lytic Cycle: Virus replicates and lyses host cell, releasing new virions.

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

Enveloped Viruses

• Have a lipid envelope; enter and exit cells by membrane fusion or budding.

• More sensitive to detergents and drying than non-enveloped viruses.

Latent Viruses

• Remain dormant in host cells; can reactivate later.

• Examples: Herpes simplex virus, Varicella-zoster virus (chickenpox/shingles).

Types of Viruses

• RNA Viruses: Influenza, HIV, West Nile virus, COVID-19 (SARS-CoV-2).

• DNA Viruses: Hepatitis B, Herpesviruses, Adenoviruses.

• Retroviruses: HIV (reverse transcriptase enzyme).

Viruses and Cancer

• Some viruses can activate oncogenes or disrupt tumor suppressor genes, leading to cancer.

• Examples: Human papillomavirus (HPV) and cervical cancer; Hepatitis B and liver cancer.

Key Epidemiological 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 Important Viruses

• Flu (Influenza): RNA virus; causes seasonal epidemics.

• Polio: RNA virus; causes poliomyelitis.

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

• Ebola: RNA virus; causes hemorrhagic fever.

• Colds: Usually caused by rhinoviruses (RNA).

• HIV and AIDS: Retrovirus; attacks immune system.

• West Nile Virus: RNA virus; transmitted by mosquitoes.

• COVID-19 (SARS-CoV-2): RNA virus; causes respiratory illness.

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