Transcript CHAPTER 27
Prokaryotes Chapter 27 • Found wherever there is life; thrive in habitats that are too cold, too hot, too salty, etc. • Most live in symbiotic relationships. • Very diverse; most abundant organism on Earth. • Prokaryotes - kingdom Monera. • 3 domains: 1 eukaryotic (Eukarya) 2 prokaryotic (Bacteria and Archae) http://www.williamsclass.com/SixthScienceWork/Classification/ClassificationNotes/images/kingdomMonera.g Structure • Most prokaryotes unicellular, can aggregate with others to become group. • 3 common cell shapes: bacilli (rodshaped), cocci (round), spirilla (helical) • Most prokaryotes have cell wall prevents internal structure from becoming hypotonic or hypertonic. • Walls - peptidoglycan (not present in archae) – sugars, polypeptides. • Gram-positive bacteria - large amount of peptidoglycan, Gramnegative - less. http://img.search.com/thumb/7/79/Gram_Stain_Anthrax.jpg/300px-Gram_Stain_Anthrax.jpg http://www.asm.org/Division/c/photo/gc1.JPG • Gram-negative bacteria more dangerous - outer membrane resists entrance of antibiotics. • Prokaryotes secrete capsule, allows organism to stick; increases resistance to host defenses. • Can adhere with pili, appendages on cell. Motility • 3 different mechanisms. – 1Flagella – 2Helical filaments (achieves corkscrew motion –similar to flagella) – 3Slime • Most move by taxis - movement towards or away from stimulus. http://www.ipm.iastate.edu/ipm/hortnews/files/images/slime%20mold.preview.jpg Cellular organization • Prokaryotes - no true nucleus. • DNA concentrated in nucleoid region. • Smaller rings of DNA – plasmid contain very few genes. • Ribosomes smaller in prokaryotes, translation similar to eukaryotes. http://www.gen.cam.ac.uk/Images/summers/plasmids.jpg Reproduction • Prokaryotes only reproduce asexually - binary fission. • 3 mechanisms for transferring genetic information. • 1Transformation occurs when prokaryote takes up information from environment. • 2Conjugation - direct transfer of genes from one to another. http://www.bio.davidson.edu/Courses/Molbio/MolStudents/spring2003/Siegenthaler/fig2.gif http://trc.ucdavis.edu/biosci10v/bis10v/week7/20f/Slide4.gif • 3Transduction - transfer from viruses to prokaryotes. • Major source of genetic variation mutation. • Growth in prokaryotes - numbers of cells, not expansion of single cell. http://web.indstate.edu/thcme/micro/bactGen/trnsduct.jpg Colony of bacteria • No limiting resources - prokaryote will continue to divide. • Conditions become too harsh, prokaryote can form endospore – resistant cell with durable wall. • Highly resistant - why disinfecting has to be exact. • Most environments, prokaryotes compete with one another. • Some secrete antibiotics to inhibit growth of other organisms. • Humans learned to use in medicine. http://io.uwinnipeg.ca/~simmons/1116/images/bactloco.gif Nutrition • Prokaryotes divided into 4 categories (nutrition). • 1Photoautotrophs - photosynthetic use light. • 2Chemoautotrophs - inorganic substances instead of light. • 3Photoheterotrophs - light to get ATP -need to get carbon in organic form. http://www.theguardians.com/Microbiology/lyngb3_bg.jpg http://sps.k12.ar.us/massengale/images/clip0089.gif • 4Chemoheterotrophs consume organic molecules for energy and carbon. • Most prokaryotes chemoheterotrophs. • Saprobes (decomposers) and parasites. • Some essential in nitrogen fixation -can survive on ability to fix nitrogen. Metabolism • Oxygen major factor in survival of prokaryotes. • Obligate aerobes- need O2 for respiration (cannot live without it) • Facultative anaerobes- can use O2 if present, can also use fermentation without it. http://www.theguardians.com/Microbiology/anaerobe.JPG http://gchava.myweb.uga.edu/Microco1.gif http://www.medschool.lsuhsc.edu/microbiology/DMIP/cpgs.jpg Diversity • Prokaryotes 1st classified according to nutrition and gram-positive, gram-negative. • Now classified according to RNA. • 2 domains, Archae and Bacteria closely related; Archae also closely related to Eukarya. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Types of Archae • Extremophiles - thrive in extreme environments. • Methanogens use CO2 to oxidize H2 – produce methane gas as waste. – Live in swamps, important decomposers. http://www.astronomy.com/asy/objects/images/methanogens_485.jpg • Extreme halophiles- live in salty conditions (Great Salt Lake). – Some require very salty conditions in order to survive. • Extreme thermophiles - extreme temperature conditions. http://serc.carleton.edu/images/microbelife/extreme/hypersaline/Halophiles_2.jpg Ecological importance • Prokaryotes decomposers - aid in recycling of nutrients throughout ecosystem. • Form symbiotic relationships with other organisms - mutualistic, commensalistic, or parasitic relationships. Fish with bioluminescent bacteria Pathogens • Some pathogens opportunistic normally reside in host without problem, can cause illness when host is weakened. • Some cause illness when they invade tissues - can produce, or endotoxins. http://www.ualberta.ca/~mmi/faculty/garmstrong/ecoli.2.gif • Exotoxins -proteins secreted by gram-positive bacteria. • Example: Cholera or Botulism • Endotoxins - components of outer membranes of gram-negative bacteria. • Example: Lyme disease Research • Scientists use prokaryotes for research - can reproduce quickly. • Some bacteria used to clean oil spills. • Some used to produce massive amounts of antibiotics, convert milk to yogurt, make vitamins.