Ch04 Lecture PPT
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Transcript of Ch04 Lecture PPT
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Archaeal
Cell Structure
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Copyright McGraw-Hill Global Education Holdings, LLC. Permission required for reproduction or display.
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4.1 A typical archaeal cell
1. Describe a typical archaeal cell.
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Archaea
Many features in common with Eukarya genes encoding protein: replication,
transcription, translation
Features in common with Bacteria genes for metabolism
Other elements are unique toArchaea
unique rRNA gene structure
capable of methanogenesis
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Archaea
Highly diverse with respect to morphology,physiology, reproduction, and ecology
Best known for growth in anaerobic,
hypersaline, pH extremes, and high-
temperature habitats
Also found in marine arctic temperature and
tropical waters
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Archaeal size, shape,
arrangement
Much like bacteria, cocci and rods are commonshapes
Other shapes can also exist
no spirochetes or mycelial forms yet
branched/flat shapes
Sizes vary (typically 1-2 x 1-5 m for rods, 1-5 m
in diameter for cocci) Smallest observed is 0.2 m in diameter
Largest is a multicellular form that can reach 30
mm in length! 5
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4.2 Archaeal cell envelopes
1. Draw an archaeal cell envelope and identify the
component layers.
2. Compare and contrast archaeal and bacterial cellenvelopes in terms of their structures, molecular
makeup, and functions.
3. Compare and contrast nutrient uptake mechanisms
observed in bacteria and archaea.
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Archaeal Cell Envelopes
Differ from bacterial envelopes in themolecular makeup and organization
S layer may be only component outside
plasma membrane
some lack cell wall
capsules and slime layers are rare
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Archaeal Membranes
Composed of uniquelipids
isoprene units (five
carbon, branched)
ether linkages rather
than ester linkages to
glycerol
Some have a monolayerstructure instead of a
bilayer structure
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Archaeal Membrane Lipids
Differ from Bacteriaand Eukaryain having
branched chain hydrocarbons attached to
glycerol by ether linkages Polar phospholipids, sulfolipids, glycolipids,
and unique lipids are also found in archaeal
membranes
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Archaea
branched chainhydrocarbons attachedto glycerol by etherlinkages
some have diglyceroltetraethers
Archaeal Lipids and Membranes
Bacteria/Eukaryotes
Fatty acids attached to
glycerol by ester linkages
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Archaeal Cell Surfaces
Cell envelopes varied S layers attached to plasma membrane
pseudomurein (peptidoglycan-like polymer)
complex polysaccharides, proteins, orglycoproteins found in some other species
only Ignicoccushas outer membrane
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Archaeal Cell Walls Differ from
Bacterial Cell Walls
Lack peptidoglycan
Most common cell wall is S layer
May have protein sheath external toS layer
S layer may be outside membrane andseparated by pseudomurein
Pseudomurein may be outermost layersimilar to Gram-positive microorganisms
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Archaeal cells and nutrient
uptake Archaeal cells use many of the same
mechanisms for nutrient uptake exhibited in
bacteria facilitated diffusion
active transport (primary and secondary)
No group translocation mechanisms have yetbeen discovered in archaea, however
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4.3 Archaeal cytoplasm
1. Compare and contrast the cytoplasm of bacterial and
archaeal cells.
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Archaeal vs. bacterial cytoplasm
Very similarlack of membrane-enclosedorganelles
May contain inclusion bodies (e.g. gas
vesicles for buoyancy control)
All the usual components
ribosomes
nucleoid region inclusion bodies
Some structures may be different,
however 20
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Ribosomes Complex structures, sites of protein synthesis
consisting of protein/RNA
Entire ribosome
bacterial/archaeal ribosome = 70S
eukaryotic (80S) S = Svedburg unit Bacterial and archaeal ribosomal RNA
16S small subunit
23S and 5S in large subunit archaea have additional 5.8S (also seen in
eukaryotic large subunit)
Proteins vary
archaea more similar to eukarya than to bacteria
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The Nucleoid
Irregularly shaped region in bacteria and
archaea
Usually not membrane bound (few
exceptions)
Location of chromosome and associatedproteins
Usually 1 (some evidence for polyploidy in
some archaeons) Supercoiling andnucleoid proteins
(histones, Alba, condensins) aid in folding
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4.4 External structures
1. Describe cannulae and hami.
2. Compare and contrast bacterial and archaeal pili.
3. Compare and contrast bacterial and archaeal flagellain terms of their structure and function.
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Archaeal external structures:
Pili not well understood as of yet
some composed of pilin protein and
homologous to bacterial type IV pili proteins pili formed have a central lumen similar to
bacterial flagella, but not bacterial pili
may be involved in archaeal adhesion
mechanisms
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Archaeal external structures:
Cannulae
hollow, tubelike structures on the surface of
thermophilic archae in the genus Pyrodictium
function is unknown
may be involved in formation of networks of multiple
daughter cells
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Archaeal external structures:
Hami
not well understood
grappling hook appearance
involvement in cell adhesion mechanisms?
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Differences of Archaeal Flagella
Flagella thinner
More than one typeof flagellin protein
Flagellum are not
hollow Hook and basal body
difficult to distinguish
More related to TypeIV secretionssystems
Growth occurs at the
base, not the end
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4.5 Comparison of BacteriaandArchaea
1. Compare and contrast bacterial and archaeal cells in
terms of the structures observed and their chemical
makeup.
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