Chapter 16 Prokaryotic vs Eukaryotic Gene Expression Regulation How to coordinate expression of related genes o Transcription Translation regulation How to regulate function of gene products once produced o Cell Signaling pathways focus of 150 o Sets of genes have to be turned on at the same time for certain signaling pathways Operons Related gene products all have the same type of promoters and enhancers Different strategies to deal with the same problem work Prokaryotic vs Eukaryotic Trp Operons Tryptophan protein cell life Operons A region of prokaryotic DNA that codes for a series of functionally related genes and is transcribed from a single promoter into a polycistronic mRNA Cistron genetic code for single polypeptide that functions as single hereditary unit Operons A unit of gene activity consisting of a sequence of genetic material that functions in a coordinated manner by means of an operator a promoter and one or more structural genes Trp and Lac Operons Trp operon not in your text Well characterized historically important They are good examples of the concept in general Tryptophan operon default ON Chapter 17 Control of Gene Expression in Bacteria Levels of Regulation o Transcriptional Control Gene Expression o Translational Control o Post translational Control Enzyme Regulation Operon o Promoter already talked about o Operator o Structural Genes Upstream Regulatory gene The operon works in conjunction with the regulator Trp Operon o Goal synthesisze tryptophan an amino acid o When If it isn t available o Why It s absolutely needed so you have to either obtain it or make it o Default setting trp production is ON Product shuts down production An example of negative feedback trpR is coding for the protein inactive repressor Tryptophan Corepressor binds to the repressor and activates it so that no RNA is made Lac Operon o Goal Metabolizing digesting Lactose sugar o When If glucose easier to process isn t available AND if lactose is available o Why Digestion is work so we want to start with easiest food forms first Also don t want to make digestive enzymes if substrate lactose isn t available o Default Setting lactose operon is OFF Lactose itself binds to the repressor turning it on allowing transcription to occur cAMP Provides Positive Regulation for lac Operon 1 cAMP cyclic AMP accumulates when glucose is scarce 2 Binds to CRP cAMP regulator protein to form active CRP complex 3 Active CRP binds to lac operon promoter and stimulates transcription Trp and Lac Operons Trp operon is repressible Lac operon is inducible Operon Regulation Options Prevent Transcription Stimulate Transcription o Positive Inducible cAMP Lac o Positive Repressible Bacterial Genome Packaging Supercoiling o Negative inducible default off remove the brakes Lac operon o Negative repressible default on apply brakes Trp operon Gene expressed in response to changes in environment Differential gene expression not all genes are expressed in all cells Prokaryotes PLUS Chromatin remodeling RNA processing splicing mRNA half life regulation DNA Packaging Multiple Levels 1 4 Different Histone Proteins 2 of the same kind Four ways in which eukaryotic gene expression via transcription is commonly regulated a DNA wraps around the nucleosomes 2 Nucleosomes 3 Chromatin Fiber 4 Looped Domains 5 Additional Folding 1 Methylation a DNA not in text OFF b Histones ON 2 Acetylation Histones ON 3 Transcription Txn 4 Translation Tln May be followed by protein regulation HAT histone acetyl transferase can be switched ON OFF HDAC histone deacetylase OFF Gene ATG start codon for translation Promoter i e TATA box Remainder of Gene s codon Terminator sequence Further upstream 5 of the TATA box are additional control elements Promoter proximal elements nearby promoter often included in promoter umbrella Distal far away enhancers PPE Es both serve to recruit transcription factors No transcription factors no More PPE E sites involved means more rapid efficient transcription initiation complex term transcription assembly Distal can also have silencers Transcription Factors bind to each other or to DNA in order to form complex Regulatory Transcription Factors bind enhancers silencers PPEs Bind to the unique regions that influence gene expression Basal Transcription Factors interact directly with promoter but are not regulatory Sequences recognized are common like TATA box Post Transcriptional Controls RNA processing splicing Unfinished RNA never leaves the nucleus mRNA degradation RNA interference small RNA sequences bind and silence mRNA may even tart it for tRNA s can t dock to ribosomes and add AA to peptide chain destruction Once a protein is made the product may still not function This is NOT regulation of gene expression IMO May need cofactor to become active May be bound by inhibitor May not be finished by post translational processing glycosylation in Golgi for Proteins all have a set of life span Once the clock runs out they are sent to recycling example plant proteasomes
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