Lecture15CMFall2009FINAL - MCB 250 Lecture 15 Transcription...

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Unformatted text preview: MCB 250 Lecture 15 Transcription in Prokaryotes (Conclusion) Transcription in Eukaryotes Transcription of the E. coli Chromosome The genome encodes ~4500 proteins. lacI lacZYA proC aroL 5’ 5’ P P 5’ 5’ +1 +1 leu azi rrnH lac gal trp his ade ser arg xyl thr rrnA rrnE rrnC rrnG rrnB rrnD 3’ 3’ Genes can be transcribed from either strand of the double helix. So RNA polymerase can attach to promoters in either strand. The direction of transcription is always 5’-3’ so the polymerases on the two strands will be moving in opposite directions. Three Types of RNA • Messenger RNA – mRNA – Template for Protein Synthesis – Unstable – Half life ≈ 3 minutes ( E. coli ) • Transfer RNA – tRNA – Adapter between mRNA and amino acids – Stable • Ribosomal RNA – rRNA – The heart of the ribosomes that synthesize protein – 5S, 16S, and 23S (Bacteria) – 5.8S, 18S, and 28S (Eukaryotes) – Stable What does “S” mean? “Svedberg Units” Sedimentation Coefficient Centrifugation can be used to separate macromolecules based on how fast they move toward the bottom of the tube – “sedimentation velocity”. Separation depends on both shape and size The functional ribosome is the 70S which is composed of one 30S subunit and one 50S subunit. The 30S subunits contains the 16S RNA while the 50S subunit contains the 23S and 5S RNAs + proteins. rRNA and tRNA Operons • E. coli has 7 rRNA operons at various positions on the chromosome • Structure: 5’ 16S – 1or 2 tRNAs – 23S – 5S – 0, 1, or 2 tRNAs – 3’ • E. coli has 79 genes that encode 46 tRNA’s – Some in rRNA operons – Some in tRNA operons – Some in mRNA (protein encoding) operons • RNA is processed to release individual rRNA’s and tRNA’s OriC Ter The arrangement of rRNA genes on the E. coli chromosome is optimized for maximal expression Arrows indicate the 7 rrn (ribosomal RNA) genes of E. coli. Processing of rRNA Transcripts in E. coli Transcription Processing - several different RNases involved 16S tRNAs 23S 5S tRNA rRNA transcripts are processed...
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This note was uploaded on 02/17/2010 for the course MCB MCB 250 taught by Professor Miller during the Fall '09 term at University of Illinois at Urbana–Champaign.

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Lecture15CMFall2009FINAL - MCB 250 Lecture 15 Transcription...

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