Study guide 6

Prokaryotic Cells

• Basic Features

  • Prokaryotic cells are unicellular organisms that lack a nucleus and membrane-bound organelles.

  • Size typically ranges from 0.5 - 5 micrometers.

  • Have specialized internal structures for different functions.

• Types of Cell Walls

  • Gram-positive bacteria: Thick layer of peptidoglycan.

  • Gram-negative bacteria: Thin layer of peptidoglycan with an outer membrane.

  • Determined through the Gram staining process.

• Cell Surface Features

  • May include capsules, pili, and flagella.

    • Capsule: Sticky outer layer that helps cells to stick to surface or other cells ( slime laye) biofilms .

    • Fimbriae: hair like appendage help cells stick to surface

    • Pili: appendage that hold cells together

    • Flagella: cells to move away or towards a stimulus taxis

    • negative taxis: away from

    • positive taxis: toward from

• Plasmids

  • Small, circular DNA molecules that are separate from chromosomal DNA.

  • May carry genes beneficial for survival and can be exchanged between bacteria.

• Endospores

  • Dormant, tough structures formed under harsh conditions to ensure survival.

  • Produced through a process under harsh conditions

  • Cell Replication

  • Prokaryotes replicate via binary fission = horizontal gene transfer between organisms

  • The chromosome is copied, and the cell divides into two identical daughter cells.

• Genetic Diversity Mechanisms

  • Transformation: cells take up foreign DNA from their surrounding. chromosome fragments or plasmids from same or other species

  • Conjugation: Direct transfer of DNA between two prokaryotic cells via a pilus.

  • Transduction: when bacteriophage viruses carry prokaryotic genes from one host to another

Prokaryotic Nutritional Modes

• Aerobes vs. Anaerobes

  • Obligate Aerobes: Require oxygen for survival.

  • Obligate Anaerobes: Poisoned by oxygen and cannot survive in its presence.

  • Facultative Anaerobes: Can survive with or without oxygen.

• Nitrogen Fixation

  • The process of converting inert atmospheric nitrogen (N₂) into a usable form (NH₃) for organisms.

  • some prokaryotes “diazotroph”

• Modes of Nutrition

  • Photoautotrophs: Use light energy to convert CO₂ into organic compounds. Autotrophic

  • Chemoautotrophs: Obtain energy from inorganic chemicals to produce organic compounds (e.g., hydrogen sulfide). Autotrophic

  • Photoheterotrophs: Use light for energy but obtain carbon from organic compounds. Heterotrophic

  • Chemoheterotrophs: Get energy and carbon from organic compounds (e.g., decomposers). Heterotrophic

Prokaryotes in Ecosystems

• Role as Decomposers

  • chemoheterotrophs

    break down waste and dead

    organisms, and recycle C, N, minerals

• Primary Producers

  • fix inorganic Co2 into organic compounds like sugars ex: autograph cyanobacteria

    Symbiotic Relationships

• Symbiosis: Interaction between two different organisms, where one may benefit at the expense of the other.

  • Host: The organism that provides the environment for the symbiont.

  • Symbiont: The organism that lives on or in the host.

• Types of Relationships that prokaryotes may have other organisms

  • Mutualism (+/+): Both organisms benefit (e.g., gut bacteria in animal receive and produce nutritient).

  • Commensalism (+/0): One organism benefits, no harm or benefit (e.g., skin bacteria).

  • Parasitism(+/-): One organism lives on or in another, harming the host (e.g., pathogens).

Gut Microbiome

• Gut Microbiome: Community of prokaryotes living in the gastrointestinal tract, playing roles in digestion and immunity.

• Probiotics vs. Prebiotics

  • Probiotics: Live beneficial bacteria (e.g., found in dairy yogurt). contains bacteria that does not grow in gut

  • Prebiotics: unique plant fibers that feed gut bacteria. encourages the growth of beneficial bacteria (e.g., dietary fibers).

Prokaryotic Pathogens

• Examples Prokaryotes acting as pathogens

  • Mycobacterium tuberculosis: Causes lung infections.

  • Borrelia burgdorferi: Causes Lyme disease (transmitted by ticks).

  • Clostridium botulinum: Produces a toxin leading to paralysis.

• Toxins

  • Endotoxins: Components of the bacterial cell wall (e.g., lipopolysaccharides), released when the cell is destroyed or dead.

  • Exotoxins: Proteins secreted by bacteria during growth (e.g., toxins from Clostridium tetani).

some beneficial uses of Prokaryotes in human society.

• Applications

  • Bioremediation: Use of prokaryotes to clean up pollutants.

  • Fermentation: Production of food items (e.g., yogurt, cheese).

  • Biotechnology: production of compounds e.g hormones, vitamins and antibodies

4 differences between bacteria and archaea

Bacteria

1. present in peptidoglycan cell wall

2. no growth at > 100 degrees

3. RNA polymerase one kind

4. growth inhibited by streptomycin and chloramphenicol

   Archaea

   1. same growth at > 100 degrees

   2. lack of peptidoglycan in their cell walls

   3. not inhibited

   4. several kinds

similarities

1. nuclear envelope absent

2. no membrane organelles

3. circular chromosomes