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Unformatted text preview: • • • • • 'Evidence against Chicxulub ex8nc8on link' in Biology in the News on BB the Chicxulub crater discovered in 1978 in the Yucatan of Mexico was thought to provide evidence that a meteor impact caused the Cretaceous‐Ter8ary (K‐T) mass ex8nc8on 65 million years ago that exterminated the dinosaurs but the latest evidence suggests that the Chicxulub impact may have occurred 300,000 years before the ex8nc8on event sediments studied in Mexico appear to be normal long term deposits, not due to a tsunami aPer the impact, which has been suggested to explain the apparent 300,000 year diﬀerence from reading the sediment layers these researchers suggest that volcanic ac8vity in India, not the Chicxulub impact, is more likely to have caused the K‐T mass ex8nc8on today’s factoid hSp://www.sunstar‐solu8ons.com/sunstar/geology/BigBend/Images/ Chicxulub.jpg st mid term exam 1 • • • • • • • • Wed. September 30th in class covers material through 9/23 lecture (ﬁrst 10 lectures) prac8ce ques8ons are posted; review sessions TBA Be on 8me – >10 min late will not be allowed into room Bring only your ID and pencils – All other materials have to be leP on periphery of the room 35 mul8ple choice ques8ons + 3 bonus factoid ques8ons 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 review sessions • Friday Sept 25th 1:30‐2:30pm. Melissa • Monday Sept 28th 2‐3pm. Mike • Tuesday Sept 29th 1‐3pm. Elinor and Alison BRING YOUR QUESTIONS. • All review sessions will be held in Bio Learning Lab, Rm 026 Life Sciences Bldg. (basement). • Remember, there are oﬃce hours on Monday 9:15‐11:15 AM in 026 Life Sciences, and Tuesday 10‐12:00pm in 601 Life Sciences reading for the exam • read up through ch 26 on prokaryotes • clariﬁca8on – in last lecture’s factoid slide, recently discovered Antarc8c bacteria were described as “chemoautotrophs” • a beSer term is chemolithotrophs – litho – refers to the use of inorganic compounds (iron and sulfur in this case) – note that my original correc7on (previous version of this lecture) was wrong But life did once arise on Earth http://www.whatischemistry.unina.it/merlinog4.jpg • What is life? – Replica7on • Transmission of informa7on p 40: Box 3.1 – Catalysis • Transforma7on of energy and conversion to structure http://www.mdc-berlin.de/en/research/ research_teams/intracellular_proteolysis/ Research/UPS.png The molecular basis of life on earth • • • • • nucleic acids (informa8on), proteins (structure and cataly8c func8on) lipids (energy source, membrane structure) carbohydrates (structure and energy) CHEMICAL EVOLUTION MUST HAVE PRECEDED BIOLOGICAL EVOLUTION – Monomers ‐> polymers (macromolecules) Hypothesis: organic monomers can be synthesized abio7cally Demonstra7on: organic monomers can be synthesized abio7cally hSp://www.usc.edu/dept/mda/180evolu8on/IMAGES/ Amino acids were formed RNA, the replicator We know that RNA polymers can also have cataly7c proper8es like protein enzymes “Ribozymes” An RNA world? Machinery for making polypeptidies ribosomes May have evolved during the “RNA world” leading to the macromolecular components we know today Biological evolu7on begins: the evolu7on 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 Earliest fossils Eukarya Bacteria Stromatolites ‐ structures formed by cyanobacteria‐like organisms hSp://www.usc.edu/dept/mda/180evolu8on/IMAGES/ Evolu8on of Earth’s ancient ecosystem • • • Marine photosynthe8c bacteria dominated the earth for 1‐2 billion years Before this 8me ‐ no oxygen in atmosphere Massive produc8on of oxygen for a very long 8me – Oxygenated the oceans – Oxidized most of the iron on Earth (now mined as iron ore) – Then, increased percentage of oxygen in atmosphere Enabled the evolu8on of organisms with respiratory metabolism Current composi7on of Earth’s atmosphere • hSp://en.wikipedia.org/wiki/Earth's_atmosphere#Composi8on Eukaryotes appear in the fossil record 2.3 billion years aTer prokaryotes Earliest eukaryote Fossil ~1.2 bya Earliest prokaryote fossil ~3.5 bya The 3 domains of life • • • • Bacteria Prokaryotes Archaea Eukarya (Eukaryotes) All three have in common: – Glycolysis Are Prokaryotes a monophyle1c group? http://en.wikipedia.org/wiki/Glycolysis – DNA replica8on mechanism – Transcrip8on, transla8on, gene8c code – Plasma membranes – Ribosomes 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 func8ons • For diﬀerences between two domains of Prokaryotes, see table 26.1 – Don’t have to memorize these When did Prokaryotes originate? • First fossils • First fossil evidence of cellular life • Billions of years to adapt and diversify before Eukaryotes appeared – But there was already signiﬁcant diversity – 3.5 billion years ago (bya) >3 bya >2 bya Prokaryote success • Es8mated 3x1028 bacteria and archaea cells in the ocean • “The bacteria living in a single human intes8nal tract outnumber all the humans who have ever lived” (Life 8e, p. 563) • Found in just about all imaginable environments – Many extreme environments • Most are unicellular (but some mul8cellular 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] An8bio8cs like penicillin and ampicillin interfere with pep8oglycan synthesis Bacterial cell well components are good targets for an8bio8cs. (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 • Reproduc8on is asexual • But many species can – Binary ﬁssion undergo gene8c recombina8on – e.g. E. coli bacteria use a conjuga8on system – Bacteria can also take up DNA from the environment and some8mes use the sequences as func8onal genes hSp://www.textbookoxacteriology.net/growth.html Metabolic diversity in Prokaryotes • Prokaryotes have had billions more years than eukaryotes to adapt and evolve • Much greater metabolic diversity than eukaryotes Most bacteria and archaea, all animals, fungi, and many pro7sts are which nutri7onal category? ...
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- Fall '08