Classification of microbes without nuclei
Early classification schemes had only two divisions: prokaryotes and eukaryotes. Bacteria and archaea both lack nuclei (prokaryotic), and were thought to be closely related. However, arachaea was found to share a common ancestor closer to eukaryotes. Three distinct domains now: bacteria, archaea, and eukaryotes.
Why use ribosomal RNA (rRNA) sequence?
- 1) All organisms have ribosomes and rRNA.
- 2) rRNA sequences have not changed in some places, but have changed in others (# of sequence changes is proportional to time).
- 3) rRNA is unlikely to be passed to other
- organisms by "lateral gene transfer (passing of genes to non-progeny) because of its association with multiple ribosomal proteins.
How are divisions made between archaea and bacteria?
Divisions ("clades") are made by ribosomal RNA comparison. Distance from one clade to another is a measure of sequence variation.
None on both bacteria and archaea.
Both bacteria and archaea have circular chromosomes, although bacteria does have linear in some species.
Histones are highly alkaline proteins that package and order the DNA into structural units called nucleosomes. Bacteria-- no. Archaea-- yes.
- In bacteria, some.. but in limited number of species.
- In archaea, none to date.
Yes, both bacteria and archaea spin like propellers. However, they are distinctive in molecular composition.
Unicellular or multicellular?
- Bacteria-- almost all unicellular.
- Archaea-- all unicellular.
- In bacteria, no.
- In archaea, it is unknown yet.
Structure of lipids in plasma membrane?
- In bacteria, glycerol is bonded to straight-chain fatty acids via ester linkage.
- In archaea, glycerol is bonded to branched fatty acids (synthesized from isoprene units) via ester linkage.
Cell-wall material made of???
- Almost all cell walls in bacteria include peptidoglycan which contains muramic acid.
- Cell walls in archaea vary widely among species, but no peptidoglycan or muramic acid.
Transcription and translation machinery???
In bacteria, there's one relatively simply RNA polymerase. Translation begins with formylmethionine and is poisoned by several antibiotics that don't affect archaea or eukaryotes. In archaea, they have one relatively simply RNA polymerase. Translation begins with methionine.
How to further distinguish one prokaryote from another?
- Morphology of the cell (rod,spiral, ball)
- by cell size
- physiology: what does the organism need to grow on?, and type of cell wall by looking at a Gram stain.
Gram-positive cell wall
Plasma membrane with proteins.. with an outer cell wall of peptidoglycan and polysaccharides.
Gram-negative cell wall
Plasma membrane with proteins.. with an outer cell wall of first peptidoglycan, and then an outermembrane w/ more proteins, topped off with polysaccharides.
When light energy is captured, and respiration (through electron transport chain) is used to make ATP.
When energy comes from organic molecules ---> respiration or fermentation produces ATP
Organisms that are able to make their own reduced carbon by "fixing" CO2 or CH4 (methane).
Organisms that must consume autotrophs (or the reduced carbon that an autotroph produces).
Prokaryotes and research..
- Pathogens (only bacteria so far)
- knowing their biology gives idea for preventing or treating disease (example: Mycobacterium tuberculosis).
- Useful microbes -- microbial properties and products can be exploited for industry, medicine, etc. (example: Lactococcus and cheesemaking). Scientific models -- bacteria and archaea are generally much simpler than eukaryotes -- easy
- to grow, fewer genes
- excellent tools for studying basic cellular processes (example: E. coli).