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After reading this chapter you should be able to:
• describe a typical archaeal cell
• compare and contrast bacterial and archaeal cells in terms of the structures
I.
A Typical Archaeal Cell
A.
Shape, arrangement and size
1.
Cocci, rods and unique shapes
2.
Rods are about 1-2 um wide and 1.0-5.0 um in length and cocci are usually 1-3 um in diameter
3.
There are also some very small and very large archaea
B.
Cell Organization
1.
Different kinds of lipids in archaeal plasma membranes
2.
More diverse cell walls
3.
No peptidoglycan in the cell walls, may have similar molecule called pseudomurein
4.
Capsules are not found as often in archaeal cells
II.
Archaeal Cell Envelopes
A.
Cell envelopes include the plasma membrane and any layers outside the plasma membrane
1.
Cell wall, S-layers, Capsules and Slime layers
B.
Archaeal Plasma Membranes
1.
Single layer membrane with different lipids
C.
Archaeal Cell Walls
1.
Most common type of archaeal cell wall has an S-layer made of glycoproteins or proteins.
2.
Some methanogens have an extra layer of material outside the S-layer.
3.
In some cells the S-layer is outermost and is separated from the plasma membrane by a peptidoglycan like molecule known as pseudomurin.
4.
Differences mean chemicals that affect bacterial cell walls and structure have no affect on archaeal cell walls.
III.
Archaeal Cytoplasm
A.
Similar to bacterial cytoplasm. Has inclusions, ribosomes, nucleoid and in some cases plasmids.
1.
Ribosomes are different in shape and different in nucleotide sequences. Different protein composition, archaeal ribosomes have more proteins.
2.
Nucleoid contains the chromosome which is circular and double-stranded DNA. Some archae have multiple copies of their chromosomes throughout their life cycles-polyploid.
IV.
External Structures
A.
Pili, Cannulae and Hami
1.
Many archae have pili, but not a lot is known about their structural proteins.
2.
Cannulae are unique to archae. They are hollow, tubelike structures seen on the surface of some thermophilic bacteria. Have a larger diameter than flagella. Function is unknown.
3.
Hami may function in attachment of cells to surfaces. They have the appearance of a grappling hook.
B.
Archaeal flagella and motility
1.
Not as thoroughly studied as bacterial flagella. Thinner than bacterial flagella and not hollow.
Not the same proteins as bacterial flagella. Work in a similar manner to bacterial flagella.
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© 2014 by McGraw-Hill Education. This is proprietary material solely for authorized instructor use. Not authorized for sale or distribution in any manner. This document may not be copied, scanned, duplicated, forwarded, distributed, or posted on a website, in whole or part.
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© 2014 by McGraw-Hill Education. This is proprietary material solely for authorized instructor use. Not authorized for sale or distribution in any manner. This document may not be copied, scanned, duplicated, forwarded, distributed, or posted on a website, in whole or part.
