Lect14-KR(2) - The three domains of life: Bacteria,...

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The three domains of life: Bacteria, Archaea, and Eukarya PMB/MCB 112 October 1, 2010
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Shape rods cocci rods Gram stain negative positive positive Oxygen use anaerobe aerobe anaerobe Carbon use autotroph heterotroph heterotroph (photosynthesis) Temperature thermophile mesophile mesophile (48°C) Other features lyses RBC forms spores
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Gram stain/ cell wall tree Shape tree Oxygen use tree Carbon use tree Which tree reflects the actual evolutionary relationship?
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Difficulties in determining phylogenetic relationships among bacteria: relative lack of complex structures little fossil record metabolic characteristics may change according to how a strain is cultured observable characteristics often result in conflicting trees bacteria are haploid and do not undergo sexual reproduction, so you can’t define a species as a group capable of interbreeding and having fertile offspring
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In 1940s-50s, it was discovered that DNA consists of linear sequences of nucleotides (genes) that are translated by ribosomes into proteins-the functional units of cells. Mutations in DNA create different phenotypes that are the subject of natural selection. After this, it made sense to construct phylogenetic trees based on DNA sequences, since these are the information that an organism inherits from its ancestors But what DNA sequence should we use?
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In the 1970s, Carl Woese at U. of Illinois began to focus on 16S ribosomal RNA (rRNA) 1) Performs the same function in ALL organisms from bacteria to humans 1) Has highly conserved regions good for alignment and other regions with more variability where sequence divergence occurs 3) Abundant, thousands/cell (this was really important before PCR)
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This note was uploaded on 01/19/2011 for the course C 112 taught by Professor Ryan during the Fall '10 term at University of California, Berkeley.

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Lect14-KR(2) - The three domains of life: Bacteria,...

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