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Bio 210A Organization of Bacterial Genomes and Control of Gene expression (Pre-lecture/lecture Worksheet) Use the following animations, the lecture and its PowerPoint, and your book to understand the process and answer the question below organization of bacterial genomes and mechanism of prokaryotic gene regulation The animations:”The Tryptophan Operon” and “Combination of Switches- The lac Operon” are accessible through http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter18/animations.html# FILL IN THE BLANKS 1. Bacterial genes coding for individual proteins needed for the same cellular process are organized as operons that share the same non-coding regulatory DNA sequence known as the promoter region. 2. Each of the “operon” genes is known as a structural gene. 3. Binding of the RNA polymerase to the promoter region followed by active transcription leads to the formation of a polycistronic mRNA, which represents an RNA molecule with coding sequences for protein synthesis of separate proteins. 4. Separate ribosomes are assembled on the polycistronic mRNA and initiate translation followed by termination of individual polypeptides or proteins . 5. Bacterial gene expression is controlled by modulation of specific allosteric interactions. 6. Different operons are regulated differently. Some code for proteins that are normally needed by the cell and they are usually actively transcribed. However, transcription can be inactivated by preventing RNA polymerase from transcribing the mRNA. Such operons and their genes are repressible (repressible/inducible) 7. Other operons code for proteins that are normally not produced by the cell except when they are needed. Such operons and their genes are inducible (repressible/inducible) Regulatory non-coding regions of bacterial genes 8. A non-coding DNA sequence known as the operator separates the promoter regions from the transcription initiation site of the “operon”. This region acts as the binding site of a protein known as the repressor protein. The gene encoding for the “repressor” protein is separate from the operon it controls. 9. Binding of the repressor protein to the operator DNA region prevents RNA polymerase from initiating transcription. Therefore, repressor proteins actively prevent transcription. The repressor is an allosteric protein whose shape can be modulated by the non- protein metabolites known as either the co-repressor or the inducers. 10. A second non-coding sequence located up-stream of the promoter regions is the binding site of the activator protein. The gene encoding for the “activator” protein is separate from the operon it controls. 11. Binding of the activator protein to the Activator binding DNA region is necessary for RNA polymerase to bind to the promoter . Therefore, activator proteins allow active transcription to proceed. 1 P.T.O. Learning Aid Control of Bacterial Gene Expression 1. Use information from your textbook and/or from “The Tryptophan Repressor” animation from the website http://highered.mcgrawhill.com/sites/0072437316/student_view0/chapter18/animations.html# to demonstrate your understanding of regulation of the trp operon by filling-in the following table: Tryptophan level Repressor State of operator Transcription Present CoState of repressor repressor (tryptophan) Absent Inactive Low Unbound ON High Present Present Bound OFF Active 2 2. Use information from your textbook and/or from the “Combination of Switches - the Lac Operon” animation from the following website http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter18/animations.html# to demonstrate your understanding of regulation of the lac operon by filling-in the following table: Lactose & glucose levels Inducer (allolactose) (present or absent) State of repressor (active or inactive)* State of Transcription operator (active or (Is it inactive) (occupied by a bound repressor?) No, present glucose is high absent active Repressor bound No, present glucose is high present inactive Repressor unbound Yes, present glucose is low absent active Yes, present glucose is low present CAP Protein (present or absent) CAP protein bound to CAPbinding site (Yes or No) present Glucose High present Lac Repressor (present or absent) Lactose Low Glucose High Inactive, glucose high & lactose low Lactose High Inactive, glucose is high Lactose Low Glucose Low present Repressor Inactive, lactose is low bound Lactose High Glucose Low present inactive Repressor unbound active, low glucose and high lactose (*) An active repressor protein has the conformation that allows it to bind to the operator. 2