Prescott’s Microbiology, 9th Edition
4
Archaeal Cell Structure
CHAPTER OVERVIEW
This chapter focuses on archaeal cell structure and function. It is its own domain. The organisms in this
domain occupy extreme habitats. They are also considered ancient organisms and thus, are an essential part of
a microbiology curriculum. The immense diversity of this domain prohibits lengthy discussion at this level.
LEARNING OUTCOMES
After reading this chapter you should be able to:
•
describe a typical archaeal cell
•
draw an archaeal cell envelope and identify the component layers
•
compare and contrast archaeal and bacterial cell envelopes in terms of their structure, molecular makeup,
and functions
•
compare and contrast nutrient uptake mechanisms observed in bacteria and archaea
•
compare and contrast the cytoplasm of bacterial and archaeal cells
•
describe cannulae and hami
•
compare and contrast bacterial and archaeal pili
•
compare and contrast bacterial and archaeal flagella in terms of their structure and function
•
compare and contrast bacterial and archaeal cells in terms of the structures observed and their chemical
makeup
CHAPTER OUTLINE
I.
II.
A Typical Archaeal Cell
A. Shape, arrangement and size
1. Cocci
2. Rods
3. Unique shapes including Thermoproteus tenax and Haloquadratum walsybri
4. Rods are about 1-2 um wide and 1.0-5.0 um in length
5. Cocci are usually 1-3 um in diameter
6. There are also some very small archae that have been found
B. Cell Organization
1. Different kinds of lipids in archaeal plasma membranes
2. More diverse cell walls
3. No peptidoglycan in the cell walls
4. Capsules are not found as often in archaeal cells
Archaeal Cell Envelopes
A. Cell envelopes include the plasma membrane and any layers outside the plasma membrane
1. Cell wall
2. S-layers
3. Capsules
4. Slime layers
B. Archaeal Plasma Membranes and Nutrient Uptake
1. Different lipids affect how the lipids are packed, this will affect the permeability and the
fluidity of the membrane
2. Two major types includes glycerol diether and diglycerol tetraether lipids
C. Archaeal Cell Walls
1. Most common type of archaeal cell wall has an S-layer made of glycoproteins or proteins.
2. Some have an S-layer wall.
3. Some methanogens have an extra layer of material outside the S-layer.
1
© 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.

Prescott’s Microbiology, 9th Edition
4.
In some cells the S-layer is the outermost and is separated from the plasma membrane by a
peptidoglycan like molecule known as pseudomurin.
5. All of these differences mean that chemical that affect bacterial cell wall 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.
3. Have a protein, Alba that is used to compact the chromosomes in the phylum Crenarchaeota.
The phylum Euryarchaeota have histones.
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. They are thinner than bacterial flagella and
have more than one type of subunit. The flagellum is not hollow. No homologous proteins
between archaeal and bacterial flagella. Work in a similar manner to bacterial flagella. No
alterations between run and tumble.
V. Comparison of Bacteria and Archaea
A. Differences in cell envelopes is one of the most significant features.
B. Ribosomes differ at the molecular level
C. Chromosomes in both domains are circular, double-stranded molecules.
CRITICAL THINKING
1.
Describe how the differences between Archaea and Bacteria may be influenced by the environments in
which they reside.
2.
Describe the differences between archaeal and bacterial cell walls.
3.
Upon finding a prokaryotic cell in nature, what features might be used to classify it as a member of the
archaeal domain rather than the eubacterial domain?
2
© 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.

Prescott’s Microbiology, 9th Edition
CONCEPT MAPPING CHALLENGE
Construct a concept map using the following words. Use you own linking words.
Bacteria Archaea cannulae pilin
ether linkage S-layer peptidoglycan
hami flagellum
extremophiles
lipids
ester linkage
3
© 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.
