Lecture 4: Archaeal Cell Structure Flashcards
(25 cards)
Archaea
Highly diverse and best known for grpwth in anaerobic hypersaline, pH extremes, and high-temp habitats.
Archaea shape
- cocci and rods are common
- also unique branched and flat shapes
- no spirochete or mycelial yet
Archaea size
- can be bigger than bacteria
- rods: 1-2 micro wide x 1-5 micro long
- cocci: 1-3 micro in diameter
smallest is 0.2 micro in diameter
largest is 30 mm in length.
Archaeal Cell Envelopes
- More S-layer in archaea than bacteria.
- Some lack cell walls.
- Slime layers observed and used in cell-cell interactions.
*S-layer is layer of proteins found outside plasma membrane (S stands for surface proteins)
Archaeal membranes and lipid structure
lipids in membranes differ in composition from bacteria.
* Polar phospholipids, sulfolipids, glycolipids, and unique lipids are also found in archaeal membranes.
- hydrophobic tail is made of 5 carbons (isoprene molecules).
- hydrocarbon bind to glycerol backbone by ether bonds.
- difference makes membrane more rigid/heat resistant
- Ether: 1 oxygen/2 carbons
- Ester: 2 oxygen/2 carbons
Bilayer membrane
Glycerol diether lipids: 20 carbons (1 hydrocarbon) attached to glycerol and form bilayer.
Monolayer membrane
Diglycerol tetraether lipid: 40 carbons (2 hydrocarbon) attached to 2 glycerol and form monolayer.
- only seen in archaea
- more rigid than diethers
- allows for survival in extreme conditions
Membrane lipids in archaea vs bacteria/eukaryotes
- Bacteria: fatty acids attached to glycerol by ester linkages.
- Archaea: branched chain hydrocarbons attached to glycerol by ether linkages.
Archaeal cell walls
Beyond lipid membrane more exterior is cell wall.
* In bacteria, cell wall is made of peptidoglycan.
* In archaea, peptidoglycan is universally absent.
Archaeal cell wall functions
perform same functions as in bacteria
* Mechanical strength
* Permeability barrier
* Stabilize against osmotic pressure
* Determining shape
Archaeal Cell Wall Compositions (5)
Different arrangements of same cell wall composition.
1. S-layer.
2. Extra protein/carbohydrate layer above.
3. Extra protein/carbohydrate layer below.
4. Protein/carbohydrate layer in place of S-layer.
5. Double membrane.
* S-layer proteins decorated with carbohydrates for stabilization/regulation of molecules crossing S-layer.
Archaeal S-layer structure
Can be up to 70 nm thick & tethered to plasma membrane.
* Resembles protein canopy from side or geometric pattern from top.
Pseudoperiplasmic space:
- Space between S-layer and membrane.
Depending on the carbohydrate layer, permeability of protein quarters changes.
Archaeal extracellular vesicles
vesicles composed of plasma membrane and surrounding cell wall material or S-layer.
* Cargo packed within includes cytoplasmic contents, proteins, and nucleic acids.
Function of extracellular vesicles
- intercellular gene transfer in thermophiles.
- protect DNA from denaturing in high temps.
Nanotubes
Vesicles connected with each other in long tube-like structures. These nanotubes are a way for archaea to communicate and pass genetic info.
Ribosomes Size
Same size as bacterial ribosomes.
* 70s constructed of a 50s and 30s subunit.
Ribosomes Composition
rRNA nucleotide sequence is different.
* Archaeal ribosomes have more r-proteins.
* Different composition makes archaeal ribosomes unaffected by antibiotics that target the ribosome.
* Archaea ribosomes similar to eukarya than to bacteria.
Nucleoid
Region in cytoplasm that contains the circular chromosome and nucleoid-associated proteins (NAPs).
Archaeal DNA
- Some archaea have multiple chromosomes.
- Supercoiling aids in folding and condensation.
- Have histone proteins that wrap DNA around it and bind it tightly (histones plus DNA is nucleosomes)
Archaeal external structures (Pili)
Composed of pilin proteins made in cytoplasm and anchor to protein complex in plasma membrane.
Two pili found in archaea only
- Cannulae: hollow tube structures on surface of thermophilic archaea.
- Daughter cells from cell division remain connected to each other by cannulae.
- Hami: like grappling hooks (attach cells to surface biofilm).
Archaealla
Flagella thinner than bacteria and filament is not hollow.
Motility of Archaea is powered by __
- Rotation is powered by ATP hydrolysis instead of proton motive force (bacteria).
- Using e- can generate a gradient where all protons are pushed to one side.
- This source of diffusion acts as power source + ATP.
