What is a prokaryote?
Earth’s initial life forms were prokaryotes, with the Archaea and Bacteria domains evolving as distinct branches.
- both domains inherited a simple prokaryotic cell organization from a common ancestor
How do prokaryotic cells differ from eukaryotic cells?
- Prokaryotes are characterized by their small size and unicellularity, eukaryotic cells are typically larger
- prokaryote cells’ compact size supports high rates of metabolism due to shorter diffusional distances
- Prokaryotic cells exhibit a variety of shapes, and lack membrane-bound organelles, and a nucleus.
How do cell-surface structures contribute to the success of prokaryotes?
- The cell wall provides structural support and protection
What is peptidoglycan?
Contained in bacterial cell walls, it is a network of sugar polymers cross-linked by short peptides.
What are eukaryotic cells made out of?
Cellulose (plants) or chitin (fungi)
What is a gram-stain in a cell-surface structure?
Gram stain provides a quick and effective way of distinguishing bacteria based of their cell wall characteristics.
What is gram positive and gram negative bacteria?
- gram positive bacteria exhibit simple cell walls characterized by a significant presence of external facing peptidoglycan.
- the thick layer of peptidoglycan contributes to the retention of the crystal violet stain during gram staining.
- gram negative bacteria have thinner layers of peptidoglycan and an additional outer lipopolysaccharide membrane that influences the staining process.
- lipopolysaccharide adds complexity to the cell structure and serves as a protective barrier.
What is a capsule in a cell-surface structure?
A sticky polysaccharide protein layer that many prokaryotes are surrounded by.
- capsules adhere cells to one another and surfaces and retain water, protecting other cells from desiccation.
- capsules form biofilms, communities of cells in a slimy extracellular matrix (dental plaque).
What are fimbraie? What are pilli?
- fimbraie are hair like appendages that facilitate cell adhesion to substrates, or other cells within a colony
- pilli are distinct from fimbraie, they are longer structures that play a role in the exchange of DNA between prokaryotic cells.
How do endospores contribute to the success of prokaryotes?
Some prokaryotes can produce metabolically inactive endospores, which can endure harsh conditions for extended periods (decades to sometimes centuries).
What are endospores? How do they help prokaryotes?
Compact, rounded, dormant cells that develop within prokaryotes when environmental conditions become unfavourable.
- endospore formation is triggered by various environmental stressors, and possess a tough protective coat that can resist UV light, chemicals, heat, high salt concentrations, and extreme pH levels.
- endospores remain dormant until environmental conditions become conductive to growth.
What is motility in the success of prokaryotes? How do they move?
Approximately half of all prokaryotes possess the ability to move actively (motile).
- Prokaryotes typically move using the flagella, which are whip-like appendages either distributed across the cell surface of concentrated at one or both ends of the cell.
- the flagella is constructed from distinct proteins in bacteria and archaea, suggesting independent evolutionary origins.
What are taxes in the motility of prokaryotes?
The ability to move in response to a specific stimulus (singular = taxis)
- moving toward or away from a stimulus (ex. positive phototaxis is the movement towards light).
How does the simple internal organization and DNA contribute to the success of prokaryotes?
- Prokaryotic cells are characterized by their straightforward internal structure without complex compartmentalization.
- Prokaryotes lack membrane-enclosed organelles, including a distinct nucleus, mitochondria, or chloroplasts
- prokaryotes have small genomes consisting of a single circular chromosome
What are plasmids?
Smaller circular DNA molecules that only some species of bacteria have.
- they are compact rings of DNA containing a limited number of extra genes, providing prokaryotes with additional genetic versatility.
How does reproduction contribute to the success of prokaryotes?
- prokaryotes are able to reproduce quickly by binary fission, they can divide every 1-3 hours and the speed is dependent on the environment.
- binary fission is asexual reproduction because prokaryotes are unicellular. It creates genetically identical copies of cells.
What are the three factors that contribute to genetic diversity?
- rapid reproduction
- mutations
- genetic recombination
What are mutations in prokaryote genetic variation?
- mutation rates during binary fission are low, but because of how quick binary fission is, mutations can rapidly accumulate within a population overtime.
What is genetic recombination in genetic variation?
- genetic recombination is a process where prokaryotic genetic material is exchanged between individual cells.
- this contributes to prokaryote genetic diversity.
What is horizontal gene transfer?
When genetic recombination occurs between individuals from different species.
What are the three mechanisms of genetic recombination?
transformation, transduction, and conjugation.
What is transformation in prokaryote genetic recombination?
Involves the absorption and integration of external DNA from the surrounding environment.
- this includes the uptake of DNA fragments or plastids often released from dead bacteria.
What is transduction in prokaryote genetic recombination?
The transfer of DNA segments between bacteria by bacteriophages.
bacteriophages are viruses that infect bacteria.
What is conjugation in prokaryote genetic recombination?
occurs when genetic material is exchanged between prokaryotic cells through direct physical contact
- the transfer of genetic material is unidirectional, it occurs only from the pilus-producing donor to the recipient.
- Plasmids are often transferred during conjugation
