Lecture+9+slides

Lecture Outcomes

By the end of this lecture, you should be able to:
- Describe the structural and functional adaptations that contribute to prokaryotic success.
- Describe reproduction in prokaryotes.
- Explain how genetic diversity is promoted in prokaryotes.
- Recall modes of nutrition and metabolism utilized by prokaryotes.
- Describe the diversity of prokaryotes, including three focal bacterial clades and groups included in Archaea.
- Explain the role of prokaryotes in chemical recycling and ecological interactions.
- List ways in which prokaryotes both help and harm humans.

Part 1: How are Prokaryotes SO Successful?

What are Prokaryotes?

Prokaryotes: single-celled organisms that make up domains Bacteria and Archaea.
Adapted to diverse and extreme environments.
Most abundant organisms on Earth; first organisms to inhabit Earth.
Size: Most prokaryotes are 0.5-5 µm, while eukaryotes range from 10-100 µm.
Most are unicellular, but some form colonies.
Interesting fact: "You're more microbe than you are human."

Osmosis Review

Hypertonic environment: Net movement of water is out of the cell.
Hypotonic environment: Net movement of water is into the cell.
Isotonic environment: No net movement of water; concentrations are equal inside and outside.

Cell-Surface Structures

Cell Walls

Maintains shape, protects the cell, and prevents bursting in hypotonic environments.
Most bacterial cell walls contain peptidoglycan (network of sugar polymers cross-linked by polypeptides).
Archaeal walls contain polysaccharides and proteins but lack peptidoglycan.

Gram Staining

Gram-positive: Simpler walls with a large amount of peptidoglycan.
Gram-negative: Complex walls with outer membranes containing lipopolysaccharides; less peptidoglycan.
Gram-negative bacteria are often more resistant to antibiotics, which target peptidoglycan (e.g., penicillin).

Capsules and Slime Layers

Sticky layers surrounding the cell wall:
- Capsule: dense and well-defined.
- Slime layer: less organized.
Functions: Adherence, prevention of dehydration, protection from the immune system.
Some bacteria form endospores (metabolically inactive) under nutrient or water stress.

Fimbriae and Pili

Fimbriae: Hairlike appendages for sticking to surfaces or individuals.
Pili: Longer appendages for DNA exchange between cells.

Motility

About half of prokaryotes can exhibit taxis (movement towards/away from a stimulus).
Flagella: Common structures for movement; differ in structure and function from eukaryotic flagella.

Internal Structures

Membranes

Prokaryotic cells lack complex compartmentalization.
Specialized membranes may perform metabolic functions; usually, these are infoldings of the cell membrane.

DNA

Prokaryotes have a single circular chromosome; do not have a nucleus (DNA located in the nucleoid region).
Also possess plasmids, smaller rings of independently replicating DNA.

Reproduction

Prokaryotes reproduce via binary fission, can divide every 1-3 hours under optimal conditions.
Key features of prokaryote biology include small size, rapid reproduction, and short generation times.

Genetic Diversity

Rapid reproduction, mutation, and genetic recombination enhance genetic diversity:
- Binary fission results in genetic clones but mutations can arise.
- Genetic recombination occurs via:
  - Transformation: Uptake of foreign DNA from the environment.
  - Transduction: Gene transfer via bacteriophages.
  - Conjugation: DNA transfer via direct contact (pili).
Horizontal gene transfer contributes significantly to genetic diversity.

Antibiotic Resistance

R plasmids carry resistance genes, allowing survival against antibiotics.
Resistance genes spread rapidly through horizontal gene transfer.

Part 3: Nutrition and Metabolism

Nutritional Modes

Prokaryotes categorized by energy and carbon sources:
- Phototrophs: Energy from light.
- Chemotrophs: Energy from chemicals.
- Autotrophs: Use CO2 for carbon.
- Heterotrophs: Require organic nutrients.

Types of Organisms

Photoautotrophs (light + CO2): e.g., cyanobacteria.
Chemoautotrophs: Unique to certain prokaryotes (e.g., Sulfolobus).
Photoheterotrophs: Unique to specific aquatic and salt-loving prokaryotes.
Chemoheterotrophs: Many prokaryotes and other organisms (e.g., Clostridium).

Oxygen in Metabolism

Obligate aerobes require O2.
Obligate anaerobes are poisoned by O2 and use fermentation.
Facultative anaerobes can switch between aerobic and anaerobic methods.

Nitrogen in Metabolism

Nitrogen is essential for amino acids/nucleic acids.
Prokaryotes can fix atmospheric nitrogen (N2) converting it to ammonia (NH3).

Metabolic Cooperation

Example: Anabaena exhibits specialization among cells (nitrogen fixation vs. photosynthesis).
Prokaryotic cells may form biofilms for cooperative resource access.

Part 4: Prokaryotic Diversity

Origins and Classification

Prokaryotes date back to 3.5 billion years ago and inhabit every known environment.
Genetic analysis divided prokaryotes into Bacteria and Archaea; metagenomics expands understanding of diversity.

Archaea

Contain extremophiles adapted to extreme environments.
Different clades include extreme halophiles and thermophiles.

Part 5: Roles of Prokaryotes

Ecological Roles

Prokaryotes are crucial in chemical cycling, impacting ecosystem functioning.
Form symbiotic relationships (commensalism, mutualism, parasitism).

Impact on Humans

Prokaryotes can be beneficial or harmful.
Human-associated bacteria play crucial roles in health and disease: e.g., gut microbiome.

Pathogenic Bacteria

Pathogenic bacteria (only bacterial, not archaea) cause numerous diseases; represent a small fraction of bacteria.
Bacteria typically cause disease via toxins and gene transfer.

Antibiotic Resistance and Technology

Resistance to antibiotics is rapidly evolving; bacteria can share resistance genes.
Prokaryotes hold significant benefits in biotechnology, food production, and bioremediation.