BMCB 658 Lecture Notes - Lecture 28: Chorismic Acid, Lac Operon, Tryptophan

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Rna pol with sigma binds to promoter (sigma recognizes promoter) The sigma subunit directs polymerase to promoter. The sigma subunit initiates strand separation (melting) First base incorporated is a purine, usually a. Rna polymerase holoenzyme catalyzes addition of about 4 more nucleotides. Core rna polymerase proceeds down the template, elongating the rna. Adds base that is complementary to the template strand. Rna polymerase catalyzes formation of phosphodiester bonds between incorporated ribonucleotides. Nucleotide triphosphate is hydrolyzed by polymerase, monophosphate is incorporated into mrna, ppi is released. Rate of rna polymerase catalysis is not constant: depends on dna sequence melting and other factors. Controlled by specific sequences called termination sites. Two inverted repeats with a few intervening bases. Loop back upon themselves, form h-bonds and forms a hairpin loop. Stem in mrna physically stops rna polymerase: rho termination. Rho is a homohexamer protein and is a rna-dna helicase and requires atp hydrolysis. Binds to mrna and follows polymerase down new transcript.

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