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IUB BIOL-L 211 - Transcription in Prokaryotes II
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BIOL-L211 Lecture 17 Outline of Last Lecture I. Transcription InitiationII. Binding of RNA PolymeraseIII. IsomerizationIV. Initial Transcription/Promoter EscapeOutline of Current Lecture I. ElongationII. TerminationIII. OperonsCurrent LectureTranscription in Prokaryotes III. ElongationA. RNAP catalyzes RNA synthesisB. Localized unwinding of dsDNA to ssDNA1. Once DNA is unwound, incoming NTPs enter through a specific channel in RNAP2. NTPs then find complementary base pairs in DNAa. U finds A, A finds T, C finds G, and G finds C3. RNA Synthesis: β and γ phosphates removed so phosphodiester bond can formbetween NTPs4. 8-9 RNA nucleotides can base pair to the template at a timea. RNA that is not paired exits the area via RNA exit channelThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.C. DNA zipped up as RNAP proceeds1. RNAP proceeds via a step mechanism (one base pair at a time)2. The transcription bubble size never changesD. Proofreading mechanisms1. Pyrophosphorolytic Editing:a. Replaces β and γ phosphates, which removes incorrect ribonucleotideb. Correct ribonucleotide can be inserted2. Hydrolytic Editing:a. RNAP backtracks one or more nucleotidesb. Erred sequence of RNA cut outII. TerminationA. Rho-independent termination1. Termination that occurs without the Rho protein2. Stem loop formed with C-G base pairs interacting (inverted repeats)3. Slight intermediate stretch with about 8 A:T base pairs4. A string of Uracil follows the stem loop5. RNAP is knocked off of template, stopping transcriptionB. Rho-dependent termination1. Rho Protein: transcription termination factor shaped as an open ring2. Rho protein binds to mRNA "rut sites"a. Rut sites are poorly defined; generally cytosine every 12-ish bases3. After binding, Rho travels down transcript with energy from ATP4. Rho unwinds RNA/DNA hybrid, causing RNAP to leave, terminating transcriptionIII. OperonsA. Operons are found ONLY IN PROKARYOTESB. Operon: one promoter controls the expression of multiple genesC. Transcript contains information regarding the number and identity of genesD. Genes on operons are typically related in function/activityE. Fla/che operon from Bacillus Subtilis1. Fla/che operon is responsible for flagella (one of longest operons identified thus fara. Has 32 genes and is 27,000 base pairs long2. Flagella are made up of filaments made up of flagellina. One of very few molecular motorsb. Can rotate 200 times per second3. Structures of Flagella:a. Filament: rotates to provide propulsionb. Hook: flexible connector between basal body and filament that allows filament structure to move and rotate without breaking away fromthe cell bodyc. Basal Body: connects flagellum to cell body and harnesses power for


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IUB BIOL-L 211 - Transcription in Prokaryotes II

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