Chapter 18: Prokaryotes & Viruses Formerly, the Kingdom Monera (except viruses) Kingdom ArchaebacteriaCanaerobic and aerobic bacteria adapted to extreme environments; prokaryotic; differ from eubacteria in structure of cell membrane and cell wall; RNA polymerase and ribosomal protein suggests a closer similarity to eukaryotes than to eubacteria; fewer than 100 named species, divided into 3 broad groups: MethanogensCanaerobic methane producers; most species use CO2 as a carbon source; found in soil, swamps, and the digestive tracts of grazing mammals such as cattle; produce nearly 2 trillion kg of methan (2 billion tons) of methane gas annually ThermoacidophilesCInhabit very hot environments that are often very acidic; some species can tolerate temperatures of 100 degrees C (230 d. F); require sulfur; nearly all are anaerobes Extreme HalophilesCLive in environments with a very high salt content, including the Dead Sea and the Great Salt Lake; nearly all are aerobic; all are gram negative Kingdom EubacteriaCtypically unicellular; prokaryotic; without membrane-bound organelles; nutrition mainly by absorption; reproduction by fission or budding; about 5,000 species (undoubtedly more) Chemoautotrophs, enterobacteria, pseudomonads, spriochaetes, actinomycetes, rickettsias I. Origins of Prokaryotes A. Fossil record 1. 32 billion yrs. old a. oldest eukaryote is only 2-22 billion yrs old. 2. are cyanobacteria (blue-green algae) a. photosynthetic B. Origins??? 1. Extraterrestrial origins (meteor/asteroid) 2. Divine creationCuntestable 3. Spontaneous orgins a. A.I. OparinCrussian scientist 1) attempted to describe early atmosphere 2) believed it contained no oxygen, but methane, ammonia, nitrogen and hydrogen gases 3) believed that small organic molecules spontaneously formed from inorganic gases b. The Urey-Miller hypothesis 1) tested Oparin=s theory 2) successfully produced amino acids, fatty acids, and small hydrocarbons in a chamber in the absence of oxygen a) knew this could never have worked in the presence of oxygen b) UV light would have destroyed methane and ammonia; also time problem c. current theory 1) RNA was the first self-replicating (complex) organic molecule; proteins, DNA, etc. DO NOT spontaneously form in water 2) presently, scientists think that life began on solid ground d. Lerman=s Bubble Model 1) waves and volcanic action caused bubbles in ancient oceans 2) gases, protected by bubbles, could have reacted to produce small organic molecules (could also have been tossed up onto solid ground) II. Biology of Prokaryotes A. Cell structure 1. 1-10 m (1/10 the size of eukaryotes) 2. have no membrane-bound organelles B. ecological niches 1. heterotrophs: require complex organic food sources, generally produced by other organisms a. are the Agerms@ b. frequently pathogenic (diseasecausing) 2. autotrophs: Aself@-feeding (phototrophs) chemotrophs, etc. C. Cell structure 1. cell membrane (plasma membrane) 2. cell wall a. techoic acid (archaebacteria) or peptidoglycan (most eubacteria) b. many antibiotics inhibit peptidoglycan synthesis 3. capsuleCslimy outer layer 4. nucleoid region (no organized nucleus) a. location of the single, circular chromosome 1) plasmids, additional separate pieces of DNA, exists in some bacteria 5. mesosome: inward extension of plasma membrane believed to aid in separation of DNA replicas 6. pili: used to attach to surfaces, provokes antigenic reactions in hosts, helps to avoid being phagocytized by macrophages 7. flagellum: s-shaped structure used as a propeller to aid in locomotion D. Significance of the cell wall 1. thick cell walls are affected by antibiotics (inhibition) 2. readily retain crystal violet stain (Gram positive) a. Gram negative bacteria have thinner cell walls, and do no retain crystal violet; are not susceptible to penicillin 1) requires tetracycline, streptomycin, etc to inhibit protein synthesis 3. endospores a. thick-walled, resistant bacterial forms 1) are dehydrated 2) can be germinated III. Cell form and arrangement (morphology) A. bacillus (-i): rod-like cells, in chains or singles B. cocci: single spheres C. diplococci: double spheres D. sarcina: group of 8 E. spirochaete: helix 1. different form of spirillum a) spirochaete has axial filaments b) spirillum has flagellum F. Vibrio: comma shaped IV. Reproduction A. Simple binary fission w/o mitosis or meiosis 1. very common 2. ex. E coli can divide every 20 minutes (4.7 x 1021 [4.7 sextillion]) bacteria will exist within one day V. Heterotrophy A. Decomposers gain energy through decay 1. saprobes—secrete enzymes to break down organic matter 2. are economically significant a. release ions for re-use (NO3, PO43-, etc. are part of the nitrogen cycle) B. Inhibition of saprophytic activity 1. must make conditions unfavorable, like cooking, drying, freezing, salting, heating 2. pasteurization, preservatives used to deter activity (sorbic acid, calcium proprionate) C. Some decomposers are useful 1. foods: flavoring 2. hormones, antibiotics, vitamins a. ex: E coli in human bowel releases vitamins (“normal flora”)