s09112lect5

s09112lect5 - Diversity I: The Prokaryotic Domains Chapter...

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Prokaryotic Systematics 1 BIOL 112 Diversity I: The Prokaryotic Domains Chapter 27 BIOL 112 Problems with Earliest Divergences • Mechanisms and events of origin of life not fully understood • Various models proposed: read Chapters 25 & 27 in Campbell/Reece • Life arose perhaps as early as 750 x 10 6 yrs after Earth formed (at 4.5 x 10 9 yrs bp) • Fossil record shows clear bacterial forms by about 3.5 x 10 9 yrs bp; some indirect evidence for life older than that • Earliest eukaryotic-like fossil forms at 1.5–2 x 10 9 yrs • What is lineage of early life-forms? BIOL 112 BIOL 112 BIOL 112 BIOL 112
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Prokaryotic Systematics 2 BIOL 112 BIOL 112 BIOL 112 BIOL 112 BIOL 112 BIOL 112
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Prokaryotic Systematics 3 BIOL 112 BIOL 112 BIOL 112 BIOL 112 BIOL 112 BIOL 112 “LUCA” L ast U niversal C ommon A ncestor • Postulated ancestor of all life forms on planet Divergences from LUCA could be bases of definition of Domains, But: – Trans-species transfers of genomic material (transformation, conjugation, transduction) – Endosymbiotic associations followed by genomic exchanges • How reconstruct lineages when there is no clear lineage of genomic material from single ancestor?
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Prokaryotic Systematics 4 BIOL 112 BIOL 112 BIOL 112 BIOL 112 BIOL 112 BIOL 112
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Prokaryotic Systematics 5 BIOL 112 The Prokaryotic Cell • Define prokaryotes with positive, not negative, traits • Prokaryotes are not merely defective eukaryotes BIOL 112 Morphology • Not a lot of diversity • Morphology is determined by cell wall – Bacilli rods – Cocci spheres – Spirilli long helix forms with external flagella – Vibrios short, curved rods, “commas” – Spriochaetes long helix forms with internal flagella • Cell Wall present in most prokaryotic forms. Prevents osmotic swelling; bacteria usually live in hypotonic environment BIOL 112 BIOL 112 BIOL 112 BIOL 112
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Prokaryotic Systematics 6 BIOL 112 BIOL 112 Cell Wall Biochemistry • Complicated polymer of amino sugar and short amino acid chains • Components: – N-acetyl glucosamine – N-acetyl muramic acid (bacteria-specific) – Peptides • All components are covalently crosslinked into giant polymer so that cell wall is one large macromolecule called peptidoglycan BIOL 112 Gram Positive/Gram Negative • Two basic arrangements of cell wall components: Gram Positive Thicker cell wall ! 20 nm; wall is 90% peptidoglycan, lipid content low (0–2%). Highly resistant to ethanol extraction, so gram stain will remain in cell and leave darkly stained cell Gram Negative Thinner cell wall ! 10–15 nm; contains only 20% peptidoglycan, higher lipid content (10–20%). High lipid content makes wall sensitive to ethanol extraction, so most of gram stain will be removed and leave weakly stained cell BIOL 112 BIOL 112 BIOL 112
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Prokaryotic Systematics 7 BIOL 112 BIOL 112 BIOL 112 BIOL 112 Two Fundamental Ways to Organize Cell Wall • Gram positive cells are especially sensitive to penicillin (Penicillin inhibits enzymes that synthesize cross links in wall) • Gram negative cells are less sensitive to penicillin
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This note was uploaded on 10/20/2009 for the course BIOL 112 taught by Professor Vaughn during the Spring '08 term at Texas A&M.

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s09112lect5 - Diversity I: The Prokaryotic Domains Chapter...

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