The Prokaryotes Differences from Eukaryotes: small cells (about 1/10 the size of eukaryotes) no nuclear envelope no membrane-bound organelles (e.g mitochondria) smaller ribosomes than eukaryotes little or no cytoskeleton “naked” DNA – not associated with histone proteins one main chromosome that is circular (not linear) sometimes smaller circles of DNA called plasmids

Prokaryotic cell division Review pages 156-157 (chapter 9) No diploidy, no spindle, no mitosis or meiosis After DNA replicates, the two chromosomes are pulled apart by attachment to the plasma membrane (fig. 9.3).

Prokaryotic movement Flagella do NOT have the “9+2” microtubule arrangement seen in eukaryotes. Instead, the flagella are made of a single rod of a protein called flagellin. The flagellum does not “whip” like eukaryotes; instead it rotates in its base – one of the only true rotational structures in living things.

Taxonomy of the prokaryotes Controversial and currently in a state of major revision as molecular data are incorporated. Formerly all grouped together in a single kingdom, called “Monera” Now we realize that there are two main groups, Bacteria and Archaea. Together with the Eukarya, these are recognized as the 3 main Domains of living things.

Chemoheterotrophs include: Saprotrophs decomposers and other decay-causing organisms Mutualists e.g. N-fixing bacteria in beans; rumen bacteria in cows Commensals live on another living thing, but don’t affect it Parasites and Pathogens

Proteobacteria Many gram-negative* photoautotrophs. Purple sulfur bacteria But a very diverse group, many of which are heterotrophic. Includes probably the most famous bacterium, Escherischia coli *Gram-negative bacteria have an extra layer outside of their peptidoglycan wall, composed of lipopolysaccharide.

Cyanobacteria - Photoautotrophs

Spirochetes and Chamydias

Firmicutes most are gram-positive many are pathogens some, the mycoplasmas, have no cell wall at all.

Archaea Thermophiles – high temperatures Acidophiles – very low pH Halophiles – very salty environments Methanogens – methane producers