BioMG 3320 1st Edition Lecture 8Outline of Past LectureI. Basics of TranscriptionII. Transcription Cycle Outline of Current LectureI. Transcription in BacteriaII. Lac Operon in E.coliIII. Other OperonsCurrent LectureI. Transcription in Bacteria- Some genes transcribed faster than others due to the strength of the promoter- By switching sigma factors, transcription can be regulated (different proteins will be transcribed)- Near the promoter, there is a sequence that recognizes proteins that will either increaseor decrease transcription- RNA polymerase binds to the promoter site; the activator binding site is located upstream of the promoter site- When RNA is bound to the promoter, this is the basal level of transcriptionThese 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.- A repressor can bind to the operator site (site where repressors bind), which overlaps with the promoter. This prevents RNA polymerase from being able to bind to the promoter, thus stopping transcription- If the activator is bound, there is an activated level of transcription- If activator is not bound, RNA polymerase is in a closed state. If the activator is there, RNA polymerase in open state and thus transcription can commenceII. Lac Operon in E.coli- An operon consists of genes with related functions that are controlled by a single promoter; codes for multiple proteins- The lac operon allows E.coli to survive on lactose as a sugar source when glucose is limited (glucose is favorable energy source)- If there is glucose and lactose, basal level of transcription occurs (low lac operon expression; growth on glucose)- If there is glucose but no lactose, the lac operon is not transcribed (growth on glucose)- If there is no glucose, but there is lactose, there is an activated level of transcription of the lac operon (growth on lactose)- If there is no lactose but there is glucose, there is a repressor that binds stopping transcription. The repressor is regulated by allolactose- If there is no glucose but there is lactose, cAMP binds CAP activator, which enables DNA binding and activated level of transcription - Allostery: binding of inducer results in a conformational change in the protein, which precludes DNA binding- DNA binding at the lac operon: helix-turn-helix- a protein domain that binds DNA; found in CAP and lac repressorIII. Other Operons- araBAD operon: expression allows E.coli to metabolize arabinose-If there is no arabinose in environment, there is no activation of RNA polymerase-If there is arabinose in the environment, there is low glucose levels and high cAMP, which allows for binding of RNA polymerase- NtrC: ATPase which triggers polymerase to initiate closed to open transition -Some promoters regulated by NtrC also have binding sites for IHF, which bends DNA, helping to bring NtrC close to polymerase - Trp operon: encodes bunch of proteins that allows E.coli to take basic metabolites and make Trp-Low Trp levels= long strands of trp mRNA. Ribosome slows down so that full strand can be transcribed-High Trp levels= short mRNA strands; hairpin forms causing RNA polymerase to fall