Bio 201 F11 Lect 11 (True) v2r

Bio 201 F11 Lect 11 (True) v2r - Biology in the News [see...

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Unformatted text preview: Biology in the News [see folder on BB] •  •  •  •  •  •  •  in the Western US, Lyme disease (caused by the bacteria Borrelia burgdorferi) is primarily carried by the Western black legged Bck (Ixodes pacificus) whose main vertebrate host is the Western fence lizard (Sceloporus occidentalis) It was previously known that S. occidentalis produces a protein in its blood that is toxic to Borrelia and has the effect of "cleansing" Bcks of the disease It was predicted that if lizards were removed from an area, the incidence of infected Bcks would go up because more of them would feed on alternaBve hosts that do not express the toxin However, in an experiment which cleared lizards from 14 plots of 10,000 sq. meters each and marked them to make sure they did not return, the opposite result was found; the incidence of infected Bcks went down It was found that more Bcks in the experimental plots had moved over to alternaBve hosts such as female woodrats But it was also found that 95% of the Bcks that would have infested the lizards did not go onto another host, which appears to be the explanaBon of the unexpected result i.e. the ecology of Lyme disease in this area turned out to be more complicated than expected hSp:// org=NSF&cntn_id=118655&preview=false st mid term exam 1 •  •  •  •  •  •  •  •  Wed. September 28th in class covers material through Friday 9/23 lecture (first 10 lectures) pracBce quesBons will be posted; review sessions listed on next slide Be on Bme –  >10 min late will not be allowed into room Bring only your ID and pencils –  All other materials have to be led on periphery of the room 35 mulBple choice quesBons + 3 bonus bio news quesBons lowest of the three mid terms is dropped, avg. of other 2 = 60% of your grade Only documented medical/family/accident excuses accepted •  we need to be NOTIFIED before end of the day on the day of the exam Exam 1 Review Sessions •  •  •  •  •  •  held in Life Sciences 026 Monday 9/26 ‐ 2:00 ‐ 3:00 ‐ Safa Abdelhakim Monday 9/26 ‐ 4:00 ‐ 5:00 ‐ Harrison Dai Tuesday 9/27 ‐ 8:30 AM ‐ 9:30 AM ‐ Redwan Ahmed Tuesday 9/27 ‐ 10:30 ‐ 11:30 AM ‐ Dana Opulente Tuesday 9/27 ‐ 2:00 ‐ 3:00 ‐ Dana Opulente •  BRING YOUR QUESTIONS; TA’s do not make presentaBons The evoluBon of cells Cell membranes are needed to enclose and protect the molecular components -conserve and concentrate valuable macromolecules and energy sources controllable inside environment for metabolism (e.g. ion concentrations) Enclosed membranes can form spontaneously by phospholipids in aqueous solution “protocells” key properBes of protocells •  large molecules such as DNA or RNA cannot pass through lipid bilayer •  small molecules can •  => replicaBon can take place inside and the product will stay inside •  represents a system of interacBng parts •  can self‐catalyze in an ordered manner •  interior can be highly chemically disBnct from the exterior environment two different hypothesis on this early world Günter Wächtershäuser: 1st catalysis by pyrite (iron disulfide) and not proteins or RNA? ‘nucleic acid replicator first’ seems plausible except: primordial soup experiments have never produced RNA polymers DNA is not catalyBc RNA probably came before DNA evidence: •  RNA is capable of forming many complex structures and catalyBc acBviBes •  protein synthesis is carried about by RNA structures (ribosomes) •  retroviruses can synthesize DNA copies of RNA molecules by reverse transcripBon hSp://‐world/ reverse transcripBon (by the enzyme reverse transcriptase) •  how retroviruses use it •  mRNAs can get reverse transcribed into DNA and inserted into the genome –  some are called “processed pseudogenes” •  no introns http:// molecular-biology-images/data// 506/RetroTranscription.jpg –  if inserted next to a funcBonal transcripBonal promoter sequence – they can be expressed the early Earth Bmeline 4.6 bya ‐ solar system began forming pre‐life earth: hot, most water was in the atmosphere as vapor (a lot was lost to space), lots of UV radiaBon reaching surface later, Earth cooled, liquid water from comet impacts was able to persist on surface [these impacts also brought N2 and heat energy; note that Mars is thought to have had a similar early history] ~ 3.5 ‐ 4 bya ‐ life on Earth begins hSp:// portolio2007/content/297_EarlyEarth_large.html Earliest fossils Stromatolites ‐ structures formed by cyanobacteria‐like organisms •  •  •  •  EvoluBon of Earth’s ancient ecosystem Marine photosyntheBc bacteria dominated the earth for 1‐2 billion years Before this Bme ‐ no oxygen in atmosphere Massive producBon of oxygen for a very long Bme –  Oxygenated the oceans –  Oxidized most of the iron on Earth (now mined as iron ore) –  Then, increased percentage of oxygen in atmosphere Enabled the evoluBon of organisms with respiratory metabolism Current composiBon of Earth’s atmosphere hSp://'s_atmosphere#ComposiBon Eukaryotes appear in the fossil record 2.3 billion years aYer prokaryotes The 3 domains of life •  •  •  •  Bacteria Prokaryotes Archaea Eukarya (Eukaryotes) All three have in common: –  Glycolysis hSp:// –  –  –  –  DNA replicaBon mechanism TranscripBon, translaBon, geneBc code Plasma membranes Ribosomes The tree of life (an idea largely originaBng from Charles Darwin) Differences between Prokaryotes and Eukaryotes •  Prokaryotes do not have cytoskeleton •  Prokaryotes do not divide by mitosis –  They use binary fission •  Prokaryotes do not have a nucleus •  DNA is usually circular •  Prokaryotes do not have membrane‐enclosed organelles (mitochondria, chloroplasts, Golgi apparatus) –  But they can have infoldings of the plasma membrane for various funcBons •  For differences between two domains of Prokaryotes, see table 26.1 in Sadava LIFE 9th ediBon –  (Don’t have to memorize those not menBoned in lecture) When did Prokaryotes originate? •  First fossils –  3.5 billion years ago (bya) >3 bya •  First fossil evidence of cellular life >2 bya –  But there was already significant diversity •  Billions of years to adapt and diversify before Eukaryotes appeared Many prokaryotes cannot be cultured Only about 5000‐10,000 species described (depends on species definiBon) Actual number possibly in the millions Prokaryote success •  EsBmated 3x1028 bacteria and archaea cells in the ocean •  There are more bacteria in a single human intesBnal tract than all the humans who have ever existed •  Found in just about all imaginable environments –  Many extreme environments •  Most are unicellular (but some mulBcellular forms known) •  Large diversity, but three most common forms are: cocci, bacilli (rods), and helices Cell wall diversity in Prokaryotes •  Chemically very different from plant, algae, and fungal cell walls •  A major method of classifying bacteria: Gram staining ‐ [purple dye followed by iodine, then alcohol wash and a red counterstain] AnBbioBcs like penicillin and ampicillin interfere with pepBdoglycan synthesis Bacterial cell well components are good targets for anBbioBcs. (why?) Some other Prokaryote features: movement Salmonella •  Some species use flagella (structurally different from Eukaryote flagella) •  Other species –  Axial filaments •  Spiral movement a spirochaete –  Gas vesicles •  Up and down in water column a cyanobacterium Some other Prokaryote features: sex •  ReproducBon is asexual •  But many species can –  Binary fission undergo geneBc recombinaBon –  e.g. E. coli bacteria use a conjugaBon system –  Bacteria can also take up DNA from the environment and someBmes use the sequences as funcBonal genes hSp://www.textbooko| Metabolic diversity in Prokaryotes •  Prokaryotes have had billions more years than eukaryotes to adapt and evolve •  Much greater metabolic diversity than eukaryotes LIFE 9th ed Table 26.2 Most bacteria and archaea, all animals, fungi, and many proBsts are which nutriBonal category? PhotosyntheBc bacteria •  Photoautotrophs (light = energy source, C02 = carbon source) –  Cyanobacteria ‐ use chlorophyll a •  Release O2 as byproduct •  H20 = “electron donor” •  Like eukaryoBc photosynthesis –  Others use bacteriochlorophyll •  Do not release O2 LIFE 9th ed Fig. 26.9 •  Some have H2S as electron donor and release Sulfur instead of O2 •  Photoheterotrophs (light = energy source, organic carbon = carbon source) –  Purple nonsulfur bacteria hSp:// index.php/Rhodobacter chlorophyll space-filling model of chlorophyll a Carbon Hydrogen Oxygen Nitrogen Magnesium chlorophylls work as molecular “antenna” absorb light energy transferring that energy by “resonance energy transfer” to particular chlorophyll molecules at “reaction centers” of chloroplasts reaction centers transfer electrons to electron transport chain which terminates in the oxidation (“splitting”) of H2O to yield H+ and O2 photosynthesis •  in essence: much more later in the course chemolithotrophs •  Also called chemoautotrophs •  Use inorganic molecules as energy source, e.g. –  NH3 or NO2‐(nitrite) ‐> NO3‐ (nitrate) –  Or H2, H2S, Sulfur •  In the deep see near hydrothermal vents –  CommuniBes exist with no light –  Inorganic molecules such as H2S come from the volcanic vents hSp:// Prokaryotes and Nitrogen hSp:// •  Denitrifiers can release nitrogen (e.g. Bacillus, Pseudomonas) Bacillus anthracis –  Normally aerobic but in anaerobic condiBons: 2NO3‐+10e‐ +12H+‐>N2+6H20 •  Nitrogen fixing bacteria (e.g. Bradyrhizobium) –  Convert atmospheric N2 to ammonia*, which is usable by other organisms N2+6H ‐> 2NH3 (*note ammonia = NH3, ammonium = NH4+) •  Crucial for all other organisms •  Nitrogen in proteins, nucleic acids, etc. •  Nitrifiers: convert ammonia or nitrite to nitrate (e.g. Nitrobacter) •  Soil, ocean Nitrobacter (sold as aquarium addiBve) hSp:// hSp:// ...
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This note was uploaded on 12/16/2011 for the course BIO 201 taught by Professor True during the Fall '08 term at SUNY Stony Brook.

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