mid 23 - Prokaryotic Transcription and Regulation Chapter 4...

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Prokaryotic Transcription and Regulation Chapter 4, pp 106-130
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Prokaryotic Transcription
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DNA RNA Protein Central Dogma of Molecular Biology transcription Copying of information • During transcription , the 4 base language of DNA is simply copied into the 4 base language of RNA. translation • During protein synthesis, the 4 base language of RNA is translated into the 20-amino acid language of proteins.
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Transcription: RNA Synthesis •One DNA strand acts as a template (read in the 3’ 5’), determining the order in which ribonucleoside triphosphate (rNTP) monomers are polymerized to form a complementary RNA strand. •This polymerization reaction is catalyzed by RNA polymerase •Polymerization involves a nucleophilic attack by the 3’ oxygen in the growing RNA chain on the α phosphate if the next nucleotide to be added…resulting in a phosphodiester bond (energetically favorable). •RNA synthesis: 5’ 3’
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Gene : a segment of DNA containing the information for a single polypeptide chain or functional RNA (i.e. rRNA, tRNA, etc.) Basic Gene Structure transcription 5’ ACAU…AUG…UGA…AUGA 3’ RNA Transcribed region Regulatory elements 5’ ACAT…ATG…TGA…ATGC 3’ 3’ TGTA…TAC…ACT…TACT 5’ Promoter Terminator DNA Gene +1 Downstream (+n) Upstream (-n) RNAP The site at which RNA polymerase begins transcription is numbered +1. - Downstream: direction in which a template DNA strand is transcribed - Upstream: denotes the opposite direction - Nucleotide positions in the DNA sequence downstream are indicated by (+) and those downstream (-). Which DNA strand is the template strand?
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Transcription Process: General View Initiation Elongation Termination “Closed Complex” “Open complex” (~14 bps) (Transcription initiation is considered complete when the first two ribonucleotides of an RNA chain are linked by a phosphodiester bond.)
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Transcription Process: General View Initiation Elongation Termination (primary transcript)
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A closer look at transcription termination: Intrinsic Terminators G/C rich A rich •Terminator is usually a G/C-rich sequence followed by an A-rich sequence. •An RNA:RNA stem loop forms (more stable due to G/C-rich in stem). This is followed by the formation of DNA:RNA hybrid via A- U pairing. •Release of RNA chain since A-U base pairing is less stable and is easily dissociated.
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Rho binds RNA and moves along it using ATP RNA Pol pauses at T site Rho catches up rut T site DNA T site Rho is helicase— unwinds RNA-DNA duplex Pol, mRNA, and Rho dissociates rut T site A closer look at transcription termination: Rho-dependent Rho
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Structure of Prokaryotic RNA Polymerase Upstream DNA Downstream DNA Transcription: Prokaryotes
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The Holoenzyme: Direction of transcription Upstream Downstream Transcription in Prokaryotes Prokaryotic RNA pol is composed of 5 subunits: 2 α 2 βω –complex = Core RNA polymerase •Core pol + σ 70 factor = RNA Pol Holoenzyme σ 70 factor recognizes and binds to the promoter region
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Sigma factor ( σ ): subunit of
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