Chapter 7 - Chapter 5 & 6: DNA, chromosomes & maintenance...

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1 Chapter 5 & 6: DNA, chromosomes & maintenance of hereditary material Chapter 7 & 8: Central dogma & regulation of gene expression • allows flexible regulation of expression • alter copy number of mRNA and/or protein levels • regulation costs energy; but this is NOT wasteful RNA intermediate: wasteful? no.
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2 RNA is almost the same as DNA: RNA • is single stranded but still can base pair with self • form 3-D structures - hair pins, stem loops etc • 3-D structure is most often critical to function (e.g. tRNA)
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3 Transcription (trxn) • an complimentary RNA copy of one strand of DNA = template •trxn produces all types of RNA species [rRNA, tRNA, mRNA, snRNA] E = RNA polymerase : adds one nucleotide at a time in 5’ to 3’ direction de novo (i.e. no primer) RNA strand rapidly detaches rRNA gene trxn: Xmas tree effect as 100’s of transcripts are being made one after another. • several RNA pols used for different purposes [RNA pol I = rRNA RNA pol II = mRNA RNA pol III = tRNA, snRNA] RNA Polymerase: a complex of proteins acting in concert …
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4 Signals on DNA tell RNA pol where to start and where to stop trxn 5’ 3’ sigma-factor : auxillary protein helps ID promotor seq • leaves pol complex after ~10 nt synthesized • re-cycles to other pols RNA pol - random collision & mount DNA migrate to conserved seq = start site initiates opening of helix • asymmetric promoter (TATA box) dictates which strand serves as template, & 5’ to 3’ polymerase activity dictates rest TATA box • terminator sequence dictates where RNA pol stops trxn [bacteria mRNA are NOT modified any further] in bacteria these distance are tightly regulated
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5 • asymmetric promoter (TATA box) dictates which strand serves as template • thus one gene must transcribe in one direction • but different genes can be on either DNA strand (pointing in either direction) Eukaryotes: a nucleus • separates trxn and translation processes • process of trxn is very similar [RNA pol properties are very similar] • eukaryotes have additional regulatory steps (see chp. 8)] • newly made RNA undergoes several processing events -- increase efficiency of export and utilization (i.e. increase half-life) • very very few un-processed RNA species leave nucleus
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6 • prokaryotic mRNAs can be poly-cistronic - operon • eukaryotic mRNA are mono-cistronic • in prokaryotes translation starts soon after 5’ end of mRNA is free • in eukaryotes translation occurs after export from nucleus
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This note was uploaded on 04/02/2008 for the course BIO 2600 taught by Professor Vanburkem during the Winter '08 term at Wayne State University.

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Chapter 7 - Chapter 5 & 6: DNA, chromosomes & maintenance...

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