Prokaryotes Flashcards
Prokaryotes
- a microscopic single-celled organism which has neither a distinct nucleus with a membrane
nor other specialized organelles, including the bacteria and cyanobacteria
General characteristics
• Fall under Monera -> Archaea and Eubacteria
• First forms of life that assisted in the changes that allowed for more complex forms of life to
occur
• Can adapt to live in almost any environment and therefore are the most abundant
organisms on earth
Gram stain technique:
• 19th cen. Hans Christian Gram (Danish) physician • Categorizes bacterial species according to differences in cell wall composition Technique: • Culture bacteria • Wet mount à sample onto a slide • Stain with crystal violet + iodine à dark blue/violet • Alcohol rinse • Counterstain with red dye safranin
Structural and functional adaptations:
• Unicellular
• Small between 0.8-8μm
• 3 main shapes:
o Spherical -> Cocci
§ Diplo-, strepto-, staphylo-
o Rod-shaped -> Bacilli
o Spiral -> Spirilla
Results of staining
• Structure of bacterium’s cell wall determines
the staining response
1. Gram-positive bacteria have simpler cell
walls -> large amounts of peptidoglycan
2. Gram-negative bacteria are more complex
-> less peptidoglycan + outer membrane
containing lipopolysaccharides (carbs
bonded to lipids)
Gram –
o Violet/iodine stain -> colours/stains the thin peptidoglycan layer o Alcohol rinse removes outer lipopolysaccharide layer + blue iodine complex o Safranin stains exposed peptidoglycan layer pink
Gram +
o Violet/iodine stain -> colours/stains the thick peptidoglycan layer o Alcohol can’t remove stain complex o Safranin stains exposed peptidoglycan layer -> however dark blue stain masks red dye
Medicinal/treatment implications:
• Staining can determine whether infection is
gram positive or gram negative and therefore
the type of treatment required
medicinal/ treatment implications of Gram negative:
• Lipids of the lipopolysaccharides in the wall
are toxic, causing fever or shock
• Outer membrane helps protect it from body’s
defences
• Membrane also makes it difficult to detect
• More resistant to antibiotic than gram positive
due to membrane impeding entry of drugs
• Produces both endo and exotoxins
• Enter body through wound
Treatment à Antibiotic: streptomycin
medicinal/ treatment implications of Gram positive
• Only produces exotoxins à proteins
excreted during lifespan
• Antibiotics such as penicillin prevents
peptidoglycan cross-linking
• This results in cell wall losing functionality
Sources of antibiotics:
o Actinomycetes
o Bacillus
o Moulds
Penicillin
inhibits cell wall synthesis by activating
‘transpeptidase’
Resistance to penicillin
peniciltase
peniciltase
bond to penicillin
molecule active sight
Fluoroquinolones
inhibits DNA replication by bonding to
enzyme to prevent division
Resistance -> cell blocks bonding of enzyme
Tetracycline
binds to ribosome, thereby blocking
protein synthesis
o Resistance -> bacteria pumps compound out of
cell
1st layer -> Slime layer/capsule:
• Not always present • Made of polysaccharides or proteins • Dense -> capsule • Not well organized -> slime layer • Sticky to allow adherence to substrates or other individuals in a colony • Prevent dehydration or attack from host’s immune system
2nd layer -> outer polysaccharide layer/membrane
• Not always present
3rd layer -> cell wall
• Gives bacterium shape
• Provides protection
• Prevents from bursting in hypotonic (low-salt)
environment
• Made from peptidoglycan (modified sugars &
polypeptides)
• Encloses bacterium and anchors molecules
extending from surface
4th layer -> cell membrane
• Encloses cytoplasm
Pili (pilum singular)
• Appendages that pull two cells together prior to
DNA transfer from one cell to another
Plasmid
- Circular DNA
* Released into environment upon cell death
DNA
• Less than eukaryote • Not enclosed or compartmentalized by membrane • Circular chromosomes, located in nucleoid
Photosynthetic lamellae
- Not present always
* Can produce food
Flagella (flagellum singular)
- Aids in motility of cell
- Differs entirely from flagella of eukaryotes
- Can be many or isolated on one end
- Move in response to stimulus
Ribosomes
- Smaller than eukaryotes
- 2 sub units
- Aids in protein synthesis
Ecological importance of Prokaryotes
• Nitrogen fixers
o Fix nitrogen into a form that can be used by other organisms for protein synthesis
• Nutrient recyclers + decomposers
o Recycle chemical elements between living and non-living components (unblock carbon,
nitrogen and other elements)
• Bioremediation
o Remove pollution and pollutants from environment (oil spills, metal rusting)
• Disease
o Maintain strength of gene pool, maintain population
• Natural antibiotics
The endosymbiotic theory
• Theory stating that chloroplasts and mitochondria were integrated into eukaryotic cells
o Larger cell took in smaller cell either as prey or entered as a parasite
• Chloroplasts and mitochondria are known as à endosymbionts
• This indicates organelles in eukaryote descended from ancestral prokaryote that was engulfed by
another cell (eu or pro)
• The engulfed cell specialized into chloroplasts and mitochondria
Evidence for endosymbiotic theory
- Double membrane
o Inner membrane’s enzymes + transport pathway is similar to prokaryotes
o Outer membrane’s enzymes + transport pathway is similar to eukaryotes - Mitochondrial size similar to the size of prokaryotic organisms
- Inner folding of mitochondria (christae) similar to inner folding of prokaryotes
- Ribosomes in mitochondria are 70S, similar to ribosomes in prokaryotes
- Circular structure of mitochondrial DNA similar to plasmids in prokaryotes
- Mitochondria undergo binary fission as do prokaryotes
