02_Genes_and_genomes - MCB182 Class Notes: Genes and...

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The tree of life : Historically, life was divided in to 5 kingdoms , but later 6 because of the 3 Urkingdoms. Most bacterial look similar to one another (specks under a microscope), but there is a fundamental division between the eubacteria and archaebacteria . There are a number of classification systems, but for genome purposes there are two important divisions: the prokaryotes (bacteria) and eukaryotes . Prokaryote genomes : You may have learned that bacteria have a single circular genome with some optional plasmids. While this is true of E. coli, it is not true of many bacteria. Some bacteria have multiple chromosomes and they may even be linear. Since prokaryote genomes are fairly small, they are easy to sequence, and many bacterial genomes are available online . Prokaryotic genes : The cartoon version of a prokaryotic protein-coding gene includes a promoter, ribosome binding site ( RBS ), and open reading frame ( ORF ). Genes can be on either strand of DNA. In some genomes, there is a significant bias with 80% of the genes on one strand. This is probably due to differences in leading strand and lagging strand in DNA replication. Not all genes code for proteins. There are also RNA genes (e.g. tRNA , rRNA , RNAse P , etc.). Operons : Some genes in the same biochemical pathway are organized in operons , the most famous of which is probably the lac operon . Not all the components in the operon are required in the same stoichiometric amounts. The strength of the RBS can control the amounts. Why do operons exist? Probably for selfish reasons. .. Horizontal gene transfer : When genes are transferred between species, it is called horizontal (o r lateral ) gene transfer. Genes may be transferred via conjugation (bac te r ia l ma t ing v ia a tube), transduction
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This note was uploaded on 04/04/2010 for the course MCB 160L taught by Professor Kiger during the Spring '08 term at UC Davis.

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02_Genes_and_genomes - MCB182 Class Notes: Genes and...

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