Chapter 13
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8 terms
Terms | Definitions |
|---|---|
 How does the control of gene expression in prokaryotes differ from that of eukaryotes? | prokaryotes-just transcription Eukaryotes-transciption, translation, post translation |
| Describe the lac operon. How does it function? what happens when glucose levels are high? Low? What happens when lactose levels are high? Low? | near the lac promoter are 2 regulatory sites 1. lacO-operator-provides binding site for repressor protein 2. CAP site-activator protein binding site When lactose is absent o Lac repressor protein binds to nucleotides of lac operator site preventing RNA polymerase from transcribing lacZ, lacY, and lacA o RNA polymerase can bind but not move forward When lactose is present o Allolactose is a small effector molecule o 4 allolactose molecules binding to lac repressor prevents repressor from binding o process called induction and lac operon is inducible When both lactose and glucose are high, the lac operon is shut off o Glucose uptake casue cAMP levels to drop o CAP does not activate transcription o Bacterium used one sugar at a time, glucose When lactose is high and glucose is low, the lac operon is turned on o Allolactose levels rise and prevents lac repressor from binding to operator o CAP is bound to the CAP site o Bacterium uses lactose When lactose is low and glucose is high or low, the lac operon is shut off o Under low lactose conditions, lac repressor prevents transcription of lac operon |
| Describe the trp operon? How is it controlled? | • binding of repressor to trp operator site inhibits transcription • when tryptophan levels low, trp repressor cannot bind to operator site and operon genes transcribed • when tryptophan levels are high tryptophan turns off the trp operon |
| How is transcription regulated in eukaryotes? What is the role of the core promoter, the TATA box, regulatory elements? | Genes almost always organized individually Regulation more intricate TATA box •5'-TATAAAA-3' transcription start site Core promoter - the minimal portion of the promoter required to properly initiate transcription regulatory or response elements • recognized by regulatory proteins that control initiation of transcription • enhancers and silencers |
| What are GTFs, how to they affect transcription? | • GTF and RNA polymerase II must come together at core promoter before transcription can be controls RNA polymerase II |
| How is chromatin structure altered to regulate transcription? | Open vs closed conformation o Is the gene accessible by proteins or not if transcription is inhibited, condensed (closed) |
| what happens when DNA is methylated? What role do CpG islands have in gene expression? | Usually inhibits transcription 1. Methylation of CpF islands may prevent an activator from binding to an enhancer element 2. Converting chromatin from an open to a closed conformation • Methyl-CpG-binding proteins bind to methylated sequences and recruit proteins that condense the chromatin |
| What are microRNA's, how do they function? | microRNAs are small RNA molecules that silence the expression of pre-existing mRNAs • first synthezied as pre-microRNA • cut by dicer to relase microRNA • associates with celluar proteins to become RNA-induced silencing complex (RISC) • upon binding 2 things may happen o mRNA degraded o RISC may inhibit translation • In either case, mRNA silenced |
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