BMB 251 1st Edition Lecture 26Outline of Last Lecture I. Cell differentiationII. Types of cellular controlIII. Gene Regulatory ProteinsIV. Negative controlV. Positive controlOutline of Current Lecture VI. Clicker QuestionVII. Leucine Zipper VIII. ActivatorsIX. RepressorsX. TryptophanXI. Lac Operon/RepressorXII. Gene Regulatory ProteinsXIII. Gene Activators/RepressorsCurrent Lecture- Clicker Question 1: Why does the major groove, but not the minor groove, uniquely identify DNAbase pairs to DNA binding proteinso The patterns of potential binding partners are not symmetrical in the major groove- Leucine zipper domain: o Almost entirely alpha heliceso Always act as dimers (cannot act as monomers) Chaperones bind to the hydrophobic amino acids (to keep them from inappropriately aggregating together) until these bind to the groove sites Two binding sites have more binding strength (affinity) and allow many different binding opportunities to bind in pair with other proteins (more types/variety of binding sites)o Amino terminus: recognition helixo –COOH terminus: where dimerization occurso Come together at Leucine (hydrophobic side at chains) which come together to try and exclude water and create a hydrophobic core o Leucine molecule is located at every two turns of DNA - Activators: DNA binding proteins that bind NEAR the promoter in order to enhance RNA polymerase binding- Repressors: DNA binding proteins that bind on top of promoters to block RNA polymerase from bindingThese 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.- **The same protein can be either an activator or a repressor, depending on where it is located on the gene- Tryptophan repressor is allosterically activated by tryptophan o Not enough tryptophan in the cell does not allow efficient binding with the repressor, making inactive. And so, sigma factor can bind and keep transcribing tryptophan geneso If there is too much tryptophan, it will bind to an allosteric repressor, which binds right in the middle of sigma factor binding region. Sigma factor cannot bind and production oftryptophan ceases until it is needed in the cell againo The binding site will NEVER always be occupied, so mRNA of tryptophan never reaches the point where none is lef- Lac operon in E. coli is always under negative and positive transcriptional control by Lac repressor protein and CAP; codes for proteins required to transport disaccharide lactose into celland break it downo Repressor controls operon so that it is highly expressed only in the presence of lactose AND the absence of glucoseo Contains many operators; Lac repressor can bind to two operators at the same time and loop out intervening DNA strengthens overall interaction of Lac repressor and DNA greater levels of repression- DNA looping also allows two different proteins bound along DNA double-helix to rapidly associate; plays crucial role in bacterial gene regulation- Many bacteria and viruses have many sigma factors that bind with RNA polymerase core and their own distinct promoters allows one set of genes to be turned off and another turned on just by changing the sigma factor- Gene control region: expanse of DNA involved in regulating and initiating transcription of a gene,including promote (where GTFs and RNA polymerase assemble) and regulatory sequences (where gene regulatory proteins bind to control the rate of assembly processes at the promoter)- Gene regulatory proteins: allow gene to be turned on/off individually- Eukaryotic gene activator proteins: main function is to attract, position and modify GTFs, mediator and RNA polymerase at the promoter so transcription can begino Do this by directly acting on these components and indirectly changing the chromatin structure around the promotero GTFs, mediator, and RNA polymerase seem unable to bind to promoter without them- Four most important ways of altering chromatin: covalently modifying histones, nucleosome remodeling, nucleosome removal and nucleosome replacemento Gene activator proteins use all four of these to alter chromatin structure of promoters- Gene activators exhibit transcriptional synergy: several activator proteins work together to produce a much higher transcription rate then without them- Eukaryotes also use gene repressor proteins to regulate transcription, but unlike in prokaryotes, they do not directly compete with RNA polymerase for access to DNA- Each eukaryotic gene is regulated by many proteins, all of which must be present to express the gene at the proper level- Gene expression results from complicated computations that intracellular gene control networksperform in response to cell’s
View Full Document
Unlocking...