LIFESCI 3 Chapter Notes - Chapter 15.1: 5S Ribosomal Rna, Sigma Factor, Pyrophosphate
Document Summary
Rna polymerases: enzymes that catalyze transcription in cells and viruses. Transcription occurs in the 5" 3" direction and requires a template strand. Does not require primer to begin rna synthesis. Only one of two strands in a dna segment is used as a template. Involves defined sections of dna rather than whole molecule. Rna polymerases differ in details but share many features. Dna-dependent rna polymerases require mg2+ and all four rntps as substrates for the polymerization reaction. Rna synthesis resembles dna synthesis in terms of chemistry and mechanism. Ribonucleotides are attached to 3" oh end. 3" oh attacks the alpha phosphate of incoming rntp and releases pyrophosphate. Template dna is copied in 3" 5" direction. All cellular rna polymerases are composed of multiple polypeptides that fold together. Rna polymerase core: enzyme with 5 polypeptide subunits. Sigma factor: sixth subunit that binds transiently to the core and directs the enzyme to specific binding sites on dna.
