BIO 7 - Prokaryotic Domains - 2009 BIO153: Lecture 7 The...

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1 2009 BIO153: Lecture 7 The Prokaryotic Domains February 2, 2009 Recall that prokaryotes show great diversity in terms of their metabolic pathways . From an evolutionary standpoint, it is interesting to note that different metabolic pathways are “scattered” among lineages (e.g., photosynthetic prokaryotes do not form a monophyletic group ). This suggests that metabolic pathways are convergent in many groups (independent acquisition of a particular type of metabolism) Understanding evolutionary relationships among the prokaryotes is complicated by the phenomenon of lateral gene transfer (genes are transferred among distantly related lineages; therefore similar traits are not good indicators of close relationships!) Evidence for lateral gene transfer: 1. Often find similar DNA sequences among distantly related organisms 2. the G-C ratio (the percentage of GC nucleotide pairs in complementary strands of DNA, relative to the percentage of A-T nucleotide pairs) in a particular DNA sequence may be markedly different from the rest of the genome How does lateral gene transfer happen?
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2 Recall the modes of genetic recombination in prokaryotes: 1. the transfer of plasmids (conjugation) 2. prokaryotes take up raw DNA from environment (transformation) - e.g. prokaryotes that live in hotsprings often pick up genes from cells in same environment 3. prokaryotes may acquire genes via virus infection (transduction) 4. parasitic prokaryotes may acquire host genes (various mechanisms): e.g. Chlamydia is an obligate intracellular parasite of eukaryotes that is related to free-living bacteria; in parasitic cells, the overall genome is reduced, but there has been acquisition of some genes from host (e.g. ATP/ADP transferases) Genetic diversity among prokaryotes: on average, ~15% of genes in each prokaryotic genome studied to date are genes unique to that species
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3 the function of many prokaryotic genes is not known
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This note was uploaded on 04/25/2010 for the course BIOLOGY BIO153 taught by Professor Cordon during the Fall '10 term at University of Toronto- Toronto.

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BIO 7 - Prokaryotic Domains - 2009 BIO153: Lecture 7 The...

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