lecturenoteschap21-09-2slides

lecturenoteschap21-09-2slides - BCMB 3100 - Chapter 21...

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1 BCMB 3100 - Chapter 21 Definition of gene RNA Polymerase Gene coding vs template strand Promoter Transcription in E. coli Transcription factors mRNA processing Biological information flow
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2 _______ - a DNA sequence that is transcribed (includes genes that do not encode proteins) ______________________ ” encode proteins or RNA essential for normal activities of the cell (e.g. enzymes in basic metabolic pathways, tRNAs and rRNAs) Four Classes of RNA in living organisms ( review ) (See Table 21.1) Ribosomal RNA ( rRNA ) - ~80% of total RNA, part of ribosomes (translation machinery) Transfer RNA ( tRNA ) - ~15% of total RNA, 73-95 nucleotides long, carry activated amino acids to ribosomes during translation Messenger RNA ( mRNA ) - linear “copies” of DNA that encode genetic information. Encode primary structure of protein. ~1-3% of total RNA, relatively unstable Small RNA - may have catalytic activity and/or associate with proteins to enhance activity, some involved with RNA processing in the nucleus
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3 RNA Synthesis ( E.coli ) Transcription DNA  RNA RNA Polymerase (450 kd) (1960, Hurwitz; Weiss) (binds DNA template) 2   (holoenzyme) forms phosphodiester bond binds rNTPs 2  (core enzyme) (see Table 21.2 RNA Synthesis 1) Intiation 2) Elongation 3) Termination RNA polymerase is responsible for these function in RNA synthesis E. coli RNA polymerase synthesizes all major types of RNA: mRNA, tRNA, rRNA, small RNA
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4 Transcription in E.coli 1) RNA polymerase searches for initiation sites (~2000 in 4,000,000 bp) 2) Unwinds DNA to produce single-stranded template 3) Selects correct ribonucleotide and catalyzes the formation of phosphodiester bonds (totally processive) 4) Detects termination signals DNA template RNA polymerase Transcription factors NTPs (ATP,CTP,GTP,UTP) Mg ++ Requirements for Transcription Note: RNA Polymerase does NOT require a primer. RNA chains can be initiated de novo. Mechanism of elongation is the same as for DNA Polymerase: nucleophilic attack by 3’-OH on - phosphate of NTP
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5 Fig 21.3 • RNA polymerase reaction Fig 21.3 (cont) E.coli transcription rate: 30-85 nucleotides/sec Error rate = 10 -6 RNA Polymerase has no exonuclease activity
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6 Fig 21.5 Orientation of a gene Fig 21.6 Promoter sequences for housekeeping genes from 10 bacteriophage and bacterial genes (coding strand) Transcription is initiated at promoter sites on the DNA template
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lecturenoteschap21-09-2slides - BCMB 3100 - Chapter 21...

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