Prokaryotic ClassificationEUBACTERIA

(Bacteria)ARCHAEBACTERIA

(Archaea)EUKARYOTES

(Eukarya)

•Traditionally classified by numerical taxonomy•Now increased use of comparative biochemistry

Figure 21.9Page 351

• The word "species" is used as the basic unit in bacterial classification schemes.

• The definition of species that fits sexually reproducing organism does not fit bacteria.

• Bacteria do not interbreed but rather reproduce by asexual means.

• The term "strain" is used to show minor differences between bacteria that are closely related.

Archaebacteria• This group probably represents the first living

cells.

• They do not have peptidoglycan in the cell wall.

• They exist in unusual, extreme habitats

• Methanogens

• Extreme halophiles

• Extreme thermophiles

Extreme Thermophiles (“heat-lovers”)

• most heat tolerant prokaryotes known

• all do best above 80o C

• live in geothermically heated soil, sulfur rich hot springs, around volcanoes and hydro thermal vents

• They use hydrogen sulfide as a source of electrons for ATP formation.

Methanogens (“methane-makers”)

• They inhabit swamps, mud, sewage, and animal guts.

• They make ATP anaerobically by converting carbon dioxide and hydrogen to methane.

Extreme Halophiles (“salt-lovers”)

• These species can tolerate high salt environments such as brackish ponds, salt lakes, volcanic vents on the seafloor, great salt lake, dead sea, and the like..

• Most are heterotrophic aerobes, but some can switch to a special photosynthesis, using a unique light absorbing pigment (bacteriorhodopsin) found in their membrane, to produce ATP.

Eubacteria

• Includes most familiar bacteria

• Have fatty acids in plasma membrane

• Most have cell wall; always includes

peptidoglycan

• Classification based largely on metabolism

Prokaryotic Fission

steps (see figure 21.7, p250)

• replication of DNA, both sets of DNA are attached to the membrane

• synthesize lipids and proteins to incorporate into plasma membrane and cell wall between the 2 DNA strands to move them apart

• new membrane and wall material grows through the cell midsection and divide the cytoplasm

• results in 2 genetically equivalent daughter cells

Prokaryotic Fission - 1

DNA replication

begins

Bacterium before

DNA replication

bacterial chromosome

Figure 21.7Page 350

Prokaryotic Fission - 2

parent DNA molecule

DNA copy

DNA replication completed

Membrane growth moves DNA

molecules apart

Figure 21.7Page 350

Prokaryotic Fission - 3

New membrane and cell-wall material

deposited

Cytoplasm divided in two

Figure 21.7Page 350

Conjugation Between Cells

• A plasmid is a small circle of DNA carrying only a few genes; it is replicated indepen dently of the “main” chromosome.

• Some plasmids allow bacteria to engage in bacterial conjugation in which a pilus joins two bacteria to permit the transfer of plasmid DNA.

• A plasmid is transferred from a donor cell to a recipient cell

Conjugationnicked plasmid

in donor cellconjugation tubeto recipient cell

Transfer of plasmid

Figure 21.8Page 351