Ch. 4 - Archaeal Cell Structure

Question 1

Archaea features in common with eukaryotes

Answer 1

• The processes and molecules used to replicate and express their genomes
• both cell types have their chromosomes organized by histones

Question 2

Elements unique to archaea

Answer 2

• unique rRNA gene structure

* capable of methanogenesis

Question 3

Archaea are best known for growth in

Answer 3

• anaerobic
• hypersaline
• pH extremes
• high temp habitats 
Also found in
• marine Arctic temps and tropical waters

Question 4

Archaea cell shapes

Answer 4

• cocci
• rod
• branched shapes
• flat shapes
• curved rods
• spiral shapes
• Pleomorphic (many shaped)
• NO spirochetes
• NO mycelial

Question 5

Sizes of archaea

Answer 5

• typically 1-2 x 1-5 micro meters for rods
• typically 1-5 micro meters for cocci
• smallest ➡️ 0.2 micro meter
• largest ➡️ 30 mm in length

Question 6

Archaeal cell envelopes

Answer 6

• differ from bacterial envelopes in molecular makeup and organization

• S Layer may be only component outside plasma membrane
• some lack cell walls
• capsules and slime layers are rare
• pseudomuerin (peptidoglycan-like polymer)
• complex polysaccharides, proteins, or glycoproteins found in some other species
• only Ignicoccus has outer membrane

Question 7

Archaeal membranes

Answer 7

• composed of unique lipids:
- isoprene units (5 carbon, branched)
-ether linkages (rather than ester linkages to glycerol)
• some have a monolayer structure instead of bilayer

Question 8

archaeal membrane lipids

Answer 8

• branched chain hydrocarbons attached to glycerol by ETHER linkage
• polar phospholipids, sulfolipids, glycolipids, and unique lipids are also found in archaeal membranes

Question 9

What is the only archaea to contain an outer membrane?

Answer 9

Ignicoccus

Question 10

Archaea features common with bacteria

Answer 10

• cell structure - look like canonical prokaryotic cell
• The processes and molecules used to conserve energy
• genes for metabolism

Question 11

Archaeal and bacterial cell wall differences

Answer 11

• lack peptidoglycan
• most common cell wall is S layer
• May have protein sheath external to S Layer
• S layer May be outside membrane and separated by pseudomuerin
• pseudomuerin May be outermost layer - similar to gram-positive micro organisms

Question 12

Archaeal nutrient uptake

Answer 12

• similar to bacteria
-facilitated diffusion
-Active transport
• no group translocation mechanisms have been discovered yet

Question 13

Archaeal vs bacterial cytoplasm

Answer 13

• very similar- lack of membrane enclosed organelles

* May contain inclusion bodies (ex. gas vesicles for buoyancy control)

Question 14

Differences of Archaeal flagella

Answer 14

• flagella thinner
• more than one type of flagellin protein
• flagellum are not hollow
• hook and basal body difficult to distinguish
• more related to type IV secretions systems
• growth occurs at the base not at the end

Question 15

Cell envelope of archaea

Answer 15

• defined as the plasma membrane and everything external to it

Question 16

What can you expect to find in cytoplasm of Archaeal cells?

Answer 16

• inclusions:
-polyhydroxyalkonates
-polyphosphate granules
-glycogen granules 
-gas vacuoles
• ribosomes
• a nucleoid
• plasmids (in some cases)

Question 17

Archaeal flagellum function

Answer 17

• their rotation is powered by ATP hydrolysis

* The cell changes direction by changing the direction of flagellar rotation

Question 18

Nucleoid

Answer 18

• The irregularly shaped region in the cytoplasm of a prokaryotic cell that contains the genetic material and some proteins

Question 19

The surfaces of an archaeal membrane, both internal and external to the cell are

Answer 19

Hydrophilic

Question 20

Hami

Answer 20

• The External cell structures that resemble miniature grappling hooks
• not well understood
• involved in cell adhesion mechanism?

Question 21

S layer components

Answer 21

• glycoproteins
• protein
• may be as thick as 20 to 40 nm

Question 22

Archaeal ribosomal proteins 3 groups

Answer 22

1) those observed in all three domains of life
2) those unique to archaea
3) those observed in both archaea and eukaryotes
• all the ribosomal proteins present in both archaeal and bacterial ribosomes are also seen in eukaryotic ribosomes

Question 23

What is true regarding the RNA component of ribosomal RNA?

Answer 23

• knowing the rRNA sequence of an organism would permit you to identify it as archaeal or bacterial
• archaea were originally defined as different from bacteria on the basis of their rRNA sequences

Question 24

Cannulae

Answer 24

• hollowed tubelike structures on the surface of thermophilic archaea in the genus Pyrodictium
• function is unknown
• May be involved in the formation of networks of multiple daughter cells
• unique to archaea

Question 25

2 major types of Archaeal lipids

Answer 25

* glycerol diethers | * diglycerol tetraethers

Question 26

Glycerol diether lipids

Answer 26

* formed when two hydrocarbons are attached to glycerol | * usually hydrocarbon chains are 20 carbons in length

Question 27

Diglycerol tetraether lipids

Answer 27

* formed when two glycerol residues are linked by two long hydrocarbons that are 40 carbons in length * tetraethers are more rigid lipids then diethers * cells can adjust the overall length of the tetraethers and increased their rigidity by cycling the chains to form pentacyclic rings

Question 28

Proteins found in nucleoid

Answer 28

``` • histones • condensin • Alba Function: • Aid in folding ```

Question 29

Pseudomuerin

Answer 29

• A peptidoglycan like molecule • separate S layer from plasma membrane • differs from peptidoglycan in that it has -L amino acids instead of D amino acids and it's cross links -N-acetyltalosaminuronic acid instead of N-acetylmuramic acid -B(1-->3) glycosidic bonds instead of B(1-->4) glycosidic bonds • these differences mean that lysozyme, penicillin, and other chemicals that affect bacterial cell wall structure and synthesis have no effect on archaeal cell walls

Question 30

Branching of the hydrocarbon chains in archaeal lipids affects what?

Answer 30

• membrane fluidity and permeability

Question 31

Pili

Answer 31

* composed of pilin protein and homologous to bacterial type IV Pili proteins * pili formed have a central lumen similar to bacterial flagella * may be involved in adhesion * not well understood

Question 32

Which cell component would be involved in compacting DNA?

Answer 32

• protein

Question 33

If an archaeal cell has no cell wall, what do you expect to find?

Answer 33

• plasma membrane and a layer of slime

Question 34

The lipids of extreme thermophiles can be expected to exhibit which chemical composition?

Answer 34

• tetraether monolayers

Question 35

Phototaxis

Answer 35

• Halobacterium species can move toward the light by flagella mediated motility