Prokaryotic Classification EUBACTERIA (Bacteria) ARCHAEBACTERIA (Archaea) EUKARYOTES (Eukarya) Traditionally classified by numerical taxonomy Now increased use of comparative biochemistry Figure 21.9 Page 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 21.7 Page 350

Prokaryotic Fission - 2 parent DNA molecule DNA copy DNA replication completed Membrane growth moves DNA molecules apart Figure 21.7 Page 350

Prokaryotic Fission - 3 New membrane and cell-wall material deposited Cytoplasm divided in two Figure 21.7 Page 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

Conjugation nicked plasmid in donor cell conjugation tube to recipient cell Transfer of plasmid Figure 21.8 Page 351