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Lecture_3,_2008 - Bio 187 Fall 2008 Lecture 3 Sept 4...

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Bio 187, Fall 2008 Lecture 3, Sept 4 K INGDOMS AND D OMAINS : F OCUS ON P ROKARYOTES Associated readings Ch 4: 68-79, 92-93 (don’t worry about cell contents, but do know nucleus, mitochondria and chloroplasts) Ch 13: 283-285 (viruses) Ch 25 : all (be selective relevant to lecture) Ch 26 : all (be selective relevant to lecture) Use the summaries at the end of each chapter to match sections with lecture notes and focus on those sections How did the major taxa evolve? The division of organisms into major taxa (Kingdoms) has shifted quite a bit over the past few years because of advances in gene sequencing—DNA sequences especially are used now as the primary methodology to sort out the microbial world. Let’s start with a basic division of organisms into 6 initial groups (Kingdoms): Bacteria Archaea Protists Fungi Plants Animals (Don’t worry about defining Archaea or bacteria yet-we’ll just go with the statement that they are different enough to be put in separate kingdoms) We ended the last lecture with a question: How did the major taxa of life originate and diversify ? Our most simple starting hypothesis is that they all arose independently from a common ancestor. The phylogeny for this would look like: Howev er, there are fundamental differences between the Bacteria and Archea as a group and the other 4 kingdoms. They are so different that we often group the Bacteria and Archaea as “Prokaryotes”. The rest are clustered together as “Eukaryotes”. Bacteria Archaea Protists Fungi Plants Animals Common Ancestor
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If this is the case, then the above phylogeny needs to be rejected and a new one constructed that better captures the similarities and differences among the major taxa. Here are the summary arguments; they will be discussed through this and the next lecture. Evidence to reject the “independent origins” hypothesis 1. Prokaryotes are very different than eukaryotes in cell structure 2. Eukaryotes have elements of cell structure that suggest a common ancestry for those 4 kingdoms (one that differs from the other two) 3. Differences in genetic material and protein synthesis suggest Eukaryotes and Archaea may be related—and may have evolved after Bacteria 4. Bacteria, Archaea and Eukaryotes are all different enough from each other that they are more usefully put into 3 separate groups: 3 DOMAINS What are the differences between prokaryotes and Eukaryotes? The first major difference is compartmentalization : Both Prokaryotes and Eukaryotes have a membrane bounding the cell, but Eukaryotes also have a separate nuclear membrane and membrane bound organelles Our analogy is that the inside of Prokaryotes is more like a large room (a log cabin), while the inside of Eukaryotes is like a large house with many chambers. These “chambers” provide sites to carry out different cell functions.
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