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Lecture 8

BIO206 Lecture 8 Chapter 7.pdf

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George S Espie

Lecture 8/ Chapter 7 October-12-13 6:34 PM 3 Stages of Transcription Initiation binding of RNA polymeraseto a promotersequence Elongation sequential addition of ribonucleotides as prescribed by the DNA template strand Termination dissociation of RNA polymerase release of primary transcript from template Regulation • Cells have the same DNA, but cells produce different proteins - how? • Control of transcription is VERY IMPORTANT! Maintain protein degradation at a constant value - Increasing/ decreasing rate of synthesis of mRNA *Prokaryotes: Signals in DNA tell RNA polymerase where to start and finish First assessment of where promotermight be – upstream Success for RNA polymerase– need to be able to transcribe the whole DNA strand - Promoter - indicate starting point for RNA synthesis - Terminator - indicate stop site - Sigma factor - subunit in RNA polymerasethat recognizes the promoteron DNA ○ Recognizes different promoters ○ Released when transcription has begun (after formation of 10-13nucleotides) ○ Reunites with RNA polymeraseafter transcription RNA polymerase: The key enzyme of RNA synthesis Bacterial RNA polymeraseis a globular protein complex Composedof: • A core enzyme containing 5 subunits with the catalytic site • A core enzyme containing 5 subunits with the catalytic site • A variable regulatory factor: sigma [σ] • RNA polymeraseholoenzyme= Core + σ BacterialRNA Polymerase Prokaryotes:only one type; One very large enzyme complex! Core Enzyme Quaternary Structure: α-subunit x2 36,000Da x 2 β-subunit 150,600Da β’-subunit 155,600Da ω-subunit 10,000Da ------------------- 422,200Da Dimensions: 10 x 10 x 15 nm Variable Component: Sigma Factor (δ): between 7 and 60 different types e.g. δ70, δ32 Variation in sigma factor allows RNA polymeras
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