Chapter 4: Archaeal Cell Structure

Question 1

In the past, archaea and bacteria were jointly referred to
as ().

Answer 1

prokaryotes

Question 2

Archaea are best known for growth in () habitats

Answer 2

anaerobic, hypersaline, pH extremes, and high-temperature

Question 3

Archaeal Shape, Arrangement, and Size

() are common shapes.

Answer 3

Cocci and rods

Question 4

Archaeal Shape, Arrangement, and Size

No () forms
discovered yet.

Answer 4

spirochete-like or mycelial

Question 5

Archaeal Cell Envelopes

• (1) may be only component outside plasma
  membrane.
• Some lack (2).
• (3) are observed to mediate cell-cell interactions
  but little is known about composition and regulation.

Answer 5

1. S-layer
2. cell wall
3. Slime layers

Question 6

Archaeal Membranes

Composed of unique lipids.
* Hydrocarbons derived from (1) units (5- carbon, branched molecules).
* Hydrocarbons attached to (2) by (3) rather than ester linkages.

Answer 6

1. isoprene
2. glycerol
3. ether linkages

Question 7

Archaeal Membranes

Some have a () structure
instead of a bilayer structure.

Answer 7

monolayer

Question 8

Archaeal Membrane Lipids

Two major types:
- (1)—hydrocarbons (20 carbons) attached to glycerol.
–C20 diethers make a (2).
- (3)—2 hydrocarbons (40 carbons) attached to 2 glycerol.
–Tetraethers are (4) than diethers.
–C40 diethers make a (5).

Answer 8

1. Glycerol diether lipids
2. bilayer
3. Diglycerol tetraether lipids
4. more rigid
5. monolayer

Question 9

Archaeal Cell Envelope Compositions

• Peptidoglycan is (1) from Archaea
• Most common cell envelope is an S-layer composed of (2).
• Some could have an (3) layer above, below or in place of the S-layer.
• A few have a (4) membrane.

Answer 9

1. universally absent
2. many copies of a single protein
3. extra protein or carbohydrate
4. double

Question 10

Archaeal S-Layer Structure

1. S-layer can be up to () thick.
2. Tethered to the ().
   * Resembles a protein canopy from the side or a geometric pattern on the top.
3. S-layer proteins decorated with () for stabilization.

Answer 10

1. 70 nm
2. plasma membrane
3. carbohydrates

Question 11

Archaeal Extracellular Vesicles and Nanotubes

• Vesicles composed of the plasma membrane and the surrounding cell wall material, or simply the S-layer.
• Cargo packed within includes (1).
• Thought to be important for (2) in thermophiles to protect DNA from denaturing in high temperatures.

Answer 11

1. cytoplasmic contents, proteins, and nucleic acids
2. intracellular gene transfer

Question 12

Archaeal versus Bacterial Cytoplasm

()—lack of membrane-enclosed organelles.

May contain inclusion bodies (that is, gas vacuoles).

All the usual components:
* Ribosomes
* Nucleoid region
* Plasmids

Some structures, however, may be different.

Answer 12

Very similar

Question 13

Ribosomes

• rRNA molecule is similar size to bacteria; however, the
  (1) is different.
• (2) differs.

Answer 13

1. nucleotide sequence
2. protein composition

Question 14

Ribosomes

• Archaeal ribosomes have (1).
• The different composition makes archaeal ribosomes unaffected by (2) that target the bacterial ribosome.
• Archaea more similar to eukarya than to bacteria.

Answer 14

1. more r-proteins
2. antibiotics

Question 15

Nucleoid

Nucleoid–region in the cytoplasm that contains the circular
chromosome and (1).

Irregularly shaped region in bacteria and archaea.

Usually not membrane bound (few exceptions).

Some evidence for (2) in archaea.

(3) and nucleoid-associated proteins
* Aid in folding and chromosome condensation.
* Histones organize the chromosome into nucleosomes
that are related to those in eukaryotes.

Answer 15

1. nucleoid-associated proteins (NAPs)
2. polyploidy
3. Supercoiling

Question 16

Archaeal External Structures

Composed of pilin proteins that are made in the cytoplasm and then anchor to a protein complex in the plasma membrane.

Answer 16

Pili

Question 17

Archaeal External Structures

Two archaeal pili:
* (1)—hollow, tubelike structures on surface of thermophilic archaea.
–Shown that daughter cells that arise from cell division remain connected to each other by (1).
* (2)—resemble grappling hooks.
–May function to attach cells to surfaces.
–Seen in biofilm communities.

Answer 17

1. Cannulae
2. Hami

Question 18

Archaella and Motility

• Flagella are (1) than bacteria.
• Some made of more than one type of protein.
• Filament is (2).

Answer 18

1. thinner
2. not hollow

Question 19

Archaella and Motility

Rotation:
* Powered by (1) instead of proton motive force.
* Direction moves cell (2) rather than runs and tumbles.

(3) motility has extremely fast speeds.

Answer 19

1. ATP hydrolysis
2. forward or backwards
3. Swimming