Prokaryotes: Bacteria & Archaea

rokaryotes: Bacteria & Archaea

• Domains: Bacteria and Archaea (both are prokaryotes)

• Size:

  • Bacteria: 1–10 µm long, 0.7–1.5 µm wide

  • Much smaller than eukaryotic cells

• Comparison:

  • Eukaryotic cell = lecture hall

  • Prokaryotic cell = chair

  • Virus = pencil tip

• Fossils: Oldest known life forms (~3.5 billion years ago)

• Diversity: Over 50 bacterial phyla

🧬 Horizontal Gene Transfer in Prokaryotes

• Definition: Genes move between different species, increasing genetic diversity.

• Vertical vs. Horizontal:

  • Vertical: Parent to offspring

  • Horizontal: Between unrelated organisms

• Significance:

  • ~17% of E. coli genes come from other bacteria

  • ~80% of prokaryotic genes have undergone horizontal transfer

🦠 Prokaryotic Cell Structure & Function

🔬 Basic Cell Parts

• Appendages: Help with movement or attachment

• Cytoplasm: Gel-like fluid inside the cell

• Cell Envelope:

  • Bacteria: Peptidoglycan

  • Archaea: Polysaccharides & proteins

🧪 Gram Staining

• Gram-positive: Thick wall; treated with penicillin

• Gram-negative: Thin wall + outer membrane; treated with cephalosporins

🧬 Genetic Material

• Circular DNA + plasmids

• No nucleus or organelles

🧫 Biofilms & Quorum Sensing

• Biofilms: Dense bacterial communities

• Quorum Sensing: Bacteria sense population size and change behavior

🔁 Reproduction in Prokaryotes

• Asexual with genetic exchange

• Methods:

  • Conjugation: DNA transfer via sex pilus

  • Transformation: Absorbing free DNA from environment

  • Transduction: DNA transfer via bacteriophages

🛡 Endospores & Resistance

• Endospores: Tough, dormant structures (e.g., Clostridium tetani)

• Resistant to: Heat, disinfectants

• Diseases: Anthrax, tetanus, botulism

• Medical Use: Botox (from botulinum toxin)

🍽 Nutrition & Metabolism

🔥 Oxygen Needs

🌱 Energy Sources

• Autotrophs: Make food from light/inorganic materials (e.g., cyanobacteria)

• Heterotrophs: Use organic nutrients (e.g., most bacteria)

  • Roles: Nitrogen fixation, decomposition

  • Products: Ethanol, antibiotics

🧫 Pathogenic Bacteria

🦠 Disease Categories

🧻 Salmonella Outbreaks

• Source: Fecal contamination

• Symptoms: Diarrhea, fever, cramps (4–7 days)

• Stats: 1.35 million U.S. cases/year

• Severe Strains: E. coli O157:H7

💊 Superbugs & Antibiotic Resistance

🧠 WHO Priority List

💩 C. difficile Infection

• Risk: Age 65+, long-term antibiotics, weak immunity

• Symptoms: Severe diarrhea, colitis

• Stats: ~500,000 U.S. cases/year; ~15,000 deaths

🧫 Koch’s Postulates

1. Microbe found in sick, not healthy organisms

2. Isolate and grow in pure culture

3. Culture causes disease in healthy host

4. Re-isolate and confirm identity

• Founded by: Robert Koch (1884)

• Used for: TB, Cholera

🌋 Domain Archaea

• Differences from Bacteria:

  • Unique rRNA sequences

  • No peptidoglycan

  • Closer to Eukarya biochemically

🔥 Archaea Traits

• Membranes: Ether bonds → heat-resistant

• Extremophiles: Live in hot springs, salty lakes, etc.

• Shared Features with Eukarya: Histone proteins

🤝 Symbiosis Example

• Hawaiian Bobtail Squid + Vibrio fischeri:

  • Bacteria help squid glow for camouflage

  • Shows bacteria’s ecological importance

🧫 Protists & Eukaryotic Life Cycles — Structured Notes

🧬 Domain Eukarya — Key Features

• Nucleus: Surrounded by a nuclear envelope with pores

• Chromosomes: Organized with histone proteins

• Cytoskeleton: Made of microtubules and microfilaments

• Mitochondria: Site of ATP production

• Cilia & Flagella: For movement

• Mitosis: For asexual cell division

• Meiosis: For sexual reproduction

• Cell Walls:

  • Cellulose in plants

  • Chitin in fungi

🧫 Protists Overview

• Eukaryotic, mostly unicellular, grouped into supergroups

• Found in plankton (aquatic ecosystems)

• Modes of Nutrition:

  • Autotrophs (photosynthetic)

  • Heterotrophs (ingest/absorb food)

  • Mixotrophs (both)

• Reproduction:

  • Asexual: binary fission, budding, spore formation

  • Sexual: conjugation (e.g., Paramecium), gamete fusion

🌿 Plant-like Protists

Green Algae

• Forms: unicellular, filamentous, colonial, multicellular

• Ancestors of land plants

Red Algae

• Products: agar, carrageenan, sushi wraps (nori)

🌊 Stramenopila

Brown Algae

• Seaweeds: kelp, rockweed

• Structures: holdfast, stipe, blade, air bladder

Diatoms

• Silica cell walls (valves)

• Major phytoplankton

• Form diatomaceous earth

🧬 Alveolates

Dinoflagellates

• Cellulose plates, two flagella

• Cause red tides, produce Paralytic Shellfish Poison

• Zooxanthellae: symbionts in coral reefs

Ciliates (e.g., Paramecium)

• Cilia, oral groove, contractile vacuole

• Two nuclei: macronucleus (daily function), micronucleus (reproduction)

Apicomplexans

• Parasitic, with apical complex

• Life cycle stages: sporozoites, merozoites, gametocytes

• Examples:

  • Plasmodium → malaria (mosquito vector)

  • Toxoplasma → toxoplasmosis

🧪 Supergroup Discoba

Kinetoplastids

• Colorless heterotrophs, have kinetoplast

• Mostly parasitic

• Diseases:

  • Trypanosoma → African sleeping sickness (Tsetse fly)

  • Chagas disease → kissing bug (8M in Latin America, 300K in U.S.)

  • Leishmania spp. → leishmaniasis (12M globally, sand fly vector)

Metamonads

• Lack typical mitochondria

• Often anaerobic

Giardia lamblia

• Most common flagellate in human gut

• Causes diarrhea, cramps, nausea

• Spread via contaminated water

• Beavers = reservoir hosts

Trichomonas vaginalis

• Sexually transmitted protist

• Causes vaginitis

• ~2.3M cases in U.S., 170M globally

🧠 Other Protist Supergroups

Amoebozoans

• Amoeboids with pseudopods

• Move via cytoplasmic streaming

Rhizarians

• Foraminiferans, Radiolarians

• Have tests (shells)

• Contribute to chalk and marine sediments

Opisthokonts

• Include:

  • Choanoflagellates

  • Animals

  • Fungi

🌍 Ecological & Evolutionary Roles

• Difficult to classify:
  
  

  • Plant-like: lack protection for gametes/zygotes

  • Fungi-like: no chitin, no flagella

  • Animal-like: heterotrophic, no embryonic development

• Photoautotrophic protists:
  
  

  • Produce oxygen

  • Major part of plankton

  • Base of aquatic food chains

• Symbiosis:
  
  

  • Range from parasitism to mutualism

  • Example: Zooxanthellae in coral reefs

• Medical importance:
  
  

  • Many are pathogenic (cause disease) or parasitic (live off hosts)

🧬 Life Cycles

Haploid Life Cycle

• Dominant stage: haploid

• Steps:

  1. Haploid adult produces gametes (mitosis)

  2. Gametes fuse → diploid zygote

  3. Zygote undergoes meiosis

  4. Haploid spores grow into new haploid adults

• Common in: protists, fungi

Diploid Life Cycle

• Dominant stage: diploid

• Steps:

  1. Diploid adult produces gametes (meiosis)

  2. Gametes fuse → diploid zygote

  3. Zygote grows into new diploid adult (mitosis)

• Common in: animals

Alternation of Generations

• Alternates between:

  • Sporophyte (2n) → makes spores (meiosis)

  • Gametophyte (n) → makes gametes (mitosis)

• Fertilization → zygote → new sporophyte

• Common in: plants, some algae

🧬 Key Terms

• Haploid (n): 1 set of chromosomes (e.g., gametes, spores)

• Diploid (2n): 2 sets of chromosomes (e.g., body cells)

• Spore: A haploid reproductive cell that grows into a new organism without fusing

• Paraphyletic Group: Includes a common ancestor but not all its descendants (e.g., protists)