Bio - 200 different cell types Typical cell expresses ~20 of its genes About 1.5 of eukaryote DNA codes for protein there are large portions of DNA

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2/22/08 19.2 Histones: DNA wrapped around protein called histone, total unit called nucleosomes; DNA between nucleosomes called “linker DNA” DNA = 2 nm DNA + histone ~10 nm Second level of packing: nucleosomes pack together: ~30 nm fiber Third level: 300 nm protein scaffolding (“looped domains”) Fourth level: condensed chromosome: 700 nm Heterochromatin: condensed, cannot be transcribed Euchromatin: less compact, can be transcribed Prokaryotes Most DNA codes for protein Also some regulatory sequences - tend to be adjacent to the genes they transcribe Coding sequence: goes from start to finish without interruption For a particular biochemical pathway: all genes tend to be adjacent, and transcribed as a unit – i.e. an operon Eukaryotes Most DNA does not code for protein – 97% does not in humans Total amount of DNA is roughly 1000x greater than in prokaryotes Eukaryotes have cell differentiation - ex. humans have
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Unformatted text preview: 200 different cell types Typical cell expresses ~20% of its genes About 1.5% of eukaryote DNA codes for protein; there are large portions of DNA that we have no idea what they do acetylation of histones – adding CoCH 3 tails promotes loose chromatin structure that permits trasncription DNA methylation: add CH 3 to DNA, renders it unable to be transcribed Genetic imprinting: difference between genes inherited from mother or father – most likely has something to do with methylation Epigenetic inheritance: inheritance of traits not directly involving nucleotide sequence Fig 19.6: structure of eukaryotic gene Transcription initiation complex: group of mediator proteins, RNA polymerase II, transcription factors, promoter, activators Differences in degradation of mRNA Prokaryotes last minutes Eukaryotes last minutes to hours to days Protein factors which bind to mRNA prevent transcription...
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This note was uploaded on 04/22/2008 for the course BIO G 102 taught by Professor Walcott during the Spring '08 term at Cornell University (Engineering School).

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