transcription (1) - RNA Structure Contain ribose instead of...

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RNA Structure Contain ribose instead of deoxyribose A,G,C,U – Uracil pairs with adenine Small chemical difference from DNA, but large structural  differences: Single stranded – ability to fold into 3D shapes
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Nucleotide – Nucleoside with phosphate added
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Ribose and Deoxyribose The sugar moiety of RNA differs from that of DNA. The difference is the presence of a 3’ hydroxyl on the ribose molecule.
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RNA Structure – Types of RNA Messenger RNA (mRNA) – genes that encode proteins Ribosomal RNA (rRNA) – form the core of ribosomes Transfer RNA (tRNA) – the adaptors that link amino acids to mRNA during translation Small regulatory RNA – also called non- coding RNA
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RNA has Uracil rather than Thymine Uracil differs from thymine in the absence of a methyl group on the 5 carbon.
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Transcription: the players -RNA polymerase -Promoter -Regulatory proteins--positive and negative regulators -Shine-Dalgarno sequence on transcript (translation)
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Transcription is the primary site of control in prokaryotes Prokaryotic genes are arranged in operons Promoters drive the expression of genes
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Prokaryotic Transcription   bacteria have operons–    groups of related genes    w/ same promoter that are  transcribed polycistronically  polycistronic RNA –     multiple  genes transcribed as ONE  TRANSCRIPT  no nucleus, so transcription  and translation can occur  simultaneously 
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Coordinate Regulation Expression of several or numerous genes can be controlled simultaneously. Operon : a set of genes that are transcribed from the same promoter and controlled by the same regulatory sites. Regulon : a set of genes (and/or operons) expressed from separate promoter sites, but controlled by the same regulatory molecule. Global regulons may coordinate expression of many genes and operons, and may induce some, but repress others.
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RNA synthesis  RNAP binds, melts     DNA into open form  nucleosides added    5’   3’  so “bottom” strand   is really template
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Bacterial RNAP numbers In log-phase E. coli : ~4000 genes ~2000 core RNA polymerase molecules ~2/3 (1300) are active at a time ~1/3 (650) can bind σ subunits. ~1200 σ subunits.
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Promoters The promoter of a gene is defined as the initial RNA polymerase binding site. The transcription start site (defined as nucleotide +1) is close to the promoter and upstream of the start (AUG) codon.
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Initiation of transcription begins with promoter binding by RNAP holoenzyme holoenzyme = RNAP core + Sigma Brock Biology of Microorganisms, vol. 9, Chapter 6
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R + P RP C RP O RP I RP E abortive transcripts k 1 k -1 k 2 k -2 k 3 k -3 k 4 Described by a equilibrium constant called K I K I = RP C /(R + P) NTPs
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This note was uploaded on 06/10/2011 for the course BIO 339 taught by Professor Georgiou during the Fall '07 term at University of Texas at Austin.

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transcription (1) - RNA Structure Contain ribose instead of...

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