Prokaryotes Flashcards
what are prokaryotes?
Microscopic single-celled organism which has neither a distinct nucleus with a membrane nor other specialized organelles
How have prokaryotes survived all these years in an oxygen rich atmosphere?
They can survive in extreme environments such as the pink lakes which have a high salt concentration
Where are some places or some environments that prokaryotes can survive?
- exposure to 3 million rads (3000× fatal dose for humans)
- pH 0.03 (which is acidic enough to dissolve metals)
- near volcanic vents and has an optimal growth temperature of 100C
What are the three main shapes of prokaryotes? What are their size ranges?
» Spherical (“coccus”)
» Rod-shaped (“bacillus”)
» Spiral (“spiro-”)
- Small (0.5 – 5 µm)
What are the benefits of a cell wall for prokaryotes and what are the different types?
- Provides protection against osmotic stress
- Bacterial cell walls contain peptidoglycan (sugar and polypeptide)
- Some have naked cell wall (“gram-positive”), others have an additional cell membrane on top of the cell wall (“gram-negative”)
What is a gram stain and what does gram-positive and gram-negative mean?
a staining technique for the preliminary identification of bacteria, in which a violet dye is applied, followed by a decolorizing agent and then a red dye. The cell walls of certain bacteria (denoted Gram-positive ) retain the first dye and appear violet, while those that lose it (denoted Gram-negative ) appear red.
What is a polysaccharide and capsule?
In many prokaryotes, the cell wall is surrounded by a sticky layer of polysaccharide or protein called capsule
What is the purpose of polysaccharide and capsule?
Enables bacteria to “stick” to substrate
What are fimbriae
Hairlike appendages on the outside of the cell wall of a bacteria
What is an endospore
» Formed when faced with harsh conditions
» Highly protective, multilayer coat forms around the chromosome, water is removed and metabolism stops …
» Can remain dormant and survive until conditions are favourable again
What are Flagellum
(pl. flagella)
» Allows prokaryotes to move (up to 50× their body length per second!)
» Works like a propeller
Where does the genetic diversity of prokaryotes come from?
Result of combination of 3 main factors:
» Rapid reproduction (some as fast as 20 min)
» Mutation due to error in replication (“1 in a million, but a million comes quickly!”)
» Genetic recombination (uptake and integration of foreign DNA, including exchange of plasmids)
What is conjugation
The temporary union of two bacteria or unicellular organisms for the exchange of genetic material.
What is recombination
Rearrangement of genetic material, especially by crossing over in chromosomes or by the artificial joining of segments of DNA from different organisms.
What was the first known case of antibiotic resistance
Japan (1950s): some hospital patients with bacterial-induced diarrhoea did not respond to antibiotic treatment → some strains of bacteria have mutations that make them resistant to antibiotic
How did antibiotic resistance happen and what effect does this have on humans
Exposing bacteria to specific antibiotic kill the “normal” bacteria, leaving only the resistant mutants … which then grow without competition!
- Over-use of antibiotics is creating “superbugs”, which have multiple resistance genes
- Significant environmental threat to human survival
Where do prokaryotes get their nutrition?
- Astounding range of nutritional and metabolic adaptations
- Part of the success of prokaryotes
- All four major modes of nutrition:
Photoautotrophs
Chemoautotrophs
Photoheterotrophs
Chemoheterotrophs
What are “Obligate aerobes”?
Prokaryotes that must use O2 for cellular respiration.
What are “Obligate anerobes”?
Prokaryotes that are poisoned by O2, and either use another terminal electron acceptor (NO3- or SO4^2-) or only conduct fermentation
What are “Facultative aerobes”?
Prokaryotes that are very flexible and can work in either aerobic or anaerobic environments
What is nitrogen fixation?
N is essential for production of amino acids and nucleic acids in all organisms
- Prokaryotes (unlike eukaryotes) can get that N in many forms.
- Some prokaryotes (cyanobacteria and methanogens) incorporate N2 straight from atmosphere into ammonia (NH3)
» Critical for plants, who form symbiosis with these nitrogen-fixing prokaryotes to increase available N
What domain contains most of the prokaryotes?
domain bacteria
What are the five clades in domain bacteria based on molecular (DNA) data?
» Proteobacteria: very diverse clade, incl. nitrogen fixing bacteria
» Chlamydias: parasitic bacteria, survive only in animal cells, depend on host for resources as basic as ATP (!)
» Spirochetes: spiral, most free-living, some pathogenic parasites (eg Treponema pallidum → syphilis)
» Cyanobacteria: only prokaryotes with plant-like oxygen-generating photosynthesis (likely related to chloroplasts)
» Gram-Positive Bacteria: very diverse clade, incl. Streptomyces (→ antibiotic “streptomycin”)
What is Domain Archaea?
- Archae share traits with Bacteria and Eukarya and some are unique
- Phylogeny still uncertain
- Archae include:
» “Extremophiles”: grow in extreme salt or temperature environments
» “Methanogens”: decomposers (herbivore
intestines, sewage treatment plants …)
