Prokaryotes

1. Prokaryotes • Prokaryotes are microscopic single-celled organisms. Although you cannot see them without the aid of a microscope, their combined biomass is more than ten times that of the eukaryotes.

2. Prokaryotic Structure • size1-5mm (resolution of the human eye ~750mm) • Cell wall • main component is peptidoglycan (modified sugar polymers) • can be further differentiated performing a gram stain • positive – More peptidoglycan • negative – Less peptidoglycan • more often pathogenic • liposaccharides of the cell surface are often toxic to the host • more resistant to antibiotics • Bacteria from Achaea lack peptidoglycan but have other polysaccharides

3. Prokaryotic Structure • May contain a capsule • protects against the hosts defenses • helps it adhere to substances or to others in the colony • may also adhere to surfaces using fimbriae (tiny hair-like structures) or pili (cytoplasmic extension used to attach during conjugation)

4. Motility • flagella • hair-like structure • Most common mode of locomotion • Movement by a whip-like motion • cilia • many shorthair-like structures covering entire organism • Movement by oar-like motion • taxis -movement toward a particular stimuli • chemotaxis- toward a substrate • phototaxis- toward light • thermotaxis- toward heat

5. Internal organization of genome • lack compartmentalization • DNA located in nucleoid region • single stranded ring of DNA • may have a smaller ring called a plasmid • contains specialized genes that help it survive under other than normal conditions • example: antibiotic resistance, digestion of a special substrate, ... • Replicate independently of the DNA • can be transferred between bacteria • Ribosomes are slightly smaller that in eukaryotes • Free floating and not attached to an ER • certain antibiotics bind to them and render them useless • erythromycin & tetracyclin

6. Reproduction and Adaptation • Reproduction via binary fission • can pass characteristics via conjugation • rapidly reproduce aiding in adaptation • increases mutation rate for adaptation • slowed by lack of nutrients, poisoning by waste, competition by other microorganisms and defenses of host • presence of endospores helps them survive in harsh conditions • copy of DNA surrounded by a thick wall • Contents are dehydrated • can last centuries • Rehydration activates the endospore to become bacteria

7. Nutritional requirements • Photoautotrophs- use the sun's energy to produce energy. • need CO2 as a substrate • cyanobacteria • Chemoautotrophs- make own energy from other chemicals • may use NH3, H2S, or Fe2+as energy source • methanogens • Photoheterotrophs - use light for the production of energy but must obtain carbon from an organic source • Chemoheterotrophs - must consume organic molecules for both energy and carbon • Most prokaryotes

8. Metabolism • aerobes -use oxygen for cellular respiration • Facultative - make energy best in the presence of oxygen but can do fermentation if oxygen is not present • anaerobes- use fermentation for the production of energy • Obligate anaerobes - poisoned be oxygen and grow exclusively be fermentation • May extract energy anaerobically by the reduction of other molecules (NO3, SO4) • Nitrogen is incorporated into the organism through the process of nitrogen fixation • Some colonies may work under metabolic cooperation where organisms produce products that are in turn used by a neighboring colony • Nitrogen fixaton