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 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.

Prokaryotic energy metabolism: extremely diverse! Autotrophs – Photoautotrophs Chemoautotrophs* Heterotrophs – Photoheterotrophs* Chemoheterotrophs *no equivalent for these groups among eukaryotes

Autotrophs – get energy without relying on other living things Photoautotrophs Photosynthetic Energy from sunlight, carbon from CO2 Basically the same energy metabolism as plants Chemoautotrophs Energy from inorganic sources (iron, sulfur, etc.) Carbon from CO2 Sometimes called “chemosynthetic”

Heterotrophs – depend on other living things for energy Photoheterotrophs Like a very strange type of photosynthesis Energy still comes from sunlight Carbon comes from decomposing other living things Chemoautotrophs Energy and carbon both come from other living things Basically same energy metabolism as animals & fungi

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

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.

Relationships among the domains Bacteria and Archaea are both considered prokaryotic because they lack organelles. BUT: They diverged a very long time ago, and they are really quite different. IN FACT: Archaea are more closely related to Eukarya than they are to Bacteria.

Cyanobacteria - Photoautotrophs

Spirochetes and Chamydias

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