- 3.5 billion years old
- Dominate the biosphere
- Live in almost all conditions
- Essential to life on earth; decompose dead organisms and return vital chemicals to
- Live in all symbiotic relationships
Eukaryotic vs. Prokaryotic
- Presence of nucleus (euk)
- Internal membrane-subdivsion into may organelles (euk)
- Simpler genome, separation of the genetic material- DNA into nucleus (euk)
- Cell wall of prokaryotes has a different composition and structure.
The world of prokaryotes
Believed to have evolved from the earliest cells
Inhabit extreme environments
Considered the more “modern” prokaryotes, having evolved later
Differ from archae in structure, biochemical and physiological characteris
That is how taxonomic level above kingdom called domain has appeared
The three major lineages of life
- Domains Eukarya and Archaea share s common ancestor that lived more recently
than the ancestor common to archea and bacteria.
- Molecular studies support hypothesis that the arcaea are most closely related to
eukaryotes than they are to bacteria.
Three Domains and Five Kingdoms Structure, Function and Reproduction
- Cocci – spherical prokaryotes (diplococcic, streptococci, staphylococci)
- Bacilli – rod shaped prokaryotes
- Helices – helical prokaryotes (includes spirillla and spirochetes
- Cell wall- of bacteria contain peptidoglycan instead of the cellulose found in cell
walls of plants and some algae
Cell Wall Function
- Maintain cell shape
- Protect the cell
- Prevent the cell from bursting in hypotonic environment
- Differ in chemical composition and construction from the cells walls of protists, fungi
- Most bacterial walls contain peptidoglycan [ptg] (polymers of modified sugars cross-
liked by short polypeptides
- Based on differences in their wall structure may members of the domain Bacteria
can be separated into two groups:
Gram Positive: have simpler walls with a large amount of ptg
Gram negative: more complex with less ptg, the outer membrane
contains lipopolysacharides (carbohydrates bonded to lipids)
- The outer membrane is often toxic and protects the pathogen against host defence
and antibiotic penetration.
- Lipopolysacharides impede entry of drugs into the cells, making gram-negative
bacteria more resistant to antibiotics
- That is why, among disease-causing bacteria, gram-negative is more threatening.
- Many penicillin-like antibiotics selectively target only bacteria by prevent the cross
link in ptg.
- May prokaryotes secrete sticky substances that form an additional protection layer-
capsule outside the cell wall.
- Some prokaryotes adhere to one another or to substrate by surface appendages
- Attach to surfaces of other prokaryotes
- During conjugation help to hold partners together while DNA is transferred. Many prokaryotes are motile
- Many prokaryotes are capable of taxis movement toward or away from a stimulus
- Chemotaxis: response to chemical stimuli, toward food or oxygen (a positive
chemotaxis) or away from toxins (a negative chemotaxis)
- Most common mechanism of movement is flagellar action.
- Flagella may be scattered over entire surface or be either from both ends or from
- Differs from eukaryotic flagella in structure and function; Lack “9+2” microtubular
structure and rotate rather than whip back and forth; not covered by plasma
- Second- spirochetes-type of motility; bacteria has several helical filaments under the
outer membrane with the basal motor attached are one end or other end of cell;
rotation of the filaments forces the flexible cell to move like a corkscrew.
- Third- some prokaryotes secrete slimy chemicals and move by gliding motion that
may result from the presence of flagellar motors that lack flagellar fila