Study Guide for Chapter 6 - Microbial Regulatory Systems PDF

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Study Guide for Chapter 6 – “Metabolic Regulation” Vocabulary Activator protein Allosteric protein Attenuation Autoinducer Catabolite repression Cyclic AMP Feedback inhibition Gene expression Heat shock proteins Induction Negative control Operon, cluster of genes all transcribed on mRNA Positive control Quorum sensing Repression Repressor protein Response regulator protein Sensor kinase protein Stringent Response Two-component regulatory system

Learning Objectives Explain the regulation of gene expression in bacteria by induction, repression, positive control, catabolite repression and attenuation. Explain how cells regulate enzyme activity.

Study Questions 1. How do bacteria control what proteins are being expressed? Transcription and translation are how genes express. This is controlled by repression, induction, positive control, attenuation, and negative control. The actual enzyme can be regulated by feedback inhibition, covalent modification, protein-protein interaction, and degradation.

2. How are constitutive proteins different from inducible proteins? Constitutive proteins are needed at the same level at all times while inducible genes are only synthesized when needed. 3. Why would cells want to control what protein is expressed? Based on the need or lack there of. 4. How does the lac operon work and is it controlled positively or negatively? The lac operon is transcribed ONLY when glucose is absent and other sugar sources are needed. It is controlled negatively, as it is physically blocked by a repressor protein when lactose is not needed. An inducer protein will cause it to change its shape, fall off of the operator and allow transcription of the lac operon to proceed. 5. What is catabolic repression? A type of negative control, the repressor binds to the operator, blocking the RNA polymerase to stop transcription of an enzyme when there are enough amounts of the product it synthesizes. 6. What is an inducer? What is the inducer for the lac operon? Induction is a negative control. It affects enzyme production, binding to and turning off the repressor protein, causing it to change shape and be unable to bind to the operator. Then it cannot block transcription, and transcription occurs. This occurs in catabolic enzymes, when a cell has used all its glucose, but lactose is present, it begins synthesizing enzymes for lactose. Allolactose is an inducer for the lac operon. 7. What do repressor proteins bind to? Inactive repressor proteins are activated when there is a surplus of product, more present then the cell can use. The excess will bind to the repressor, activate it, and the repressor proteins will bind to the operator, preventing transcription of structural genes for biosynthesis of the product. No more enzymes that biosynthesize the product will be made. Corepressors bind with certain repressors in order to activate them. 8. How is positive control different from negative control?

Negative control is so named because repressor proteins are inhibitory. In positive control activation occurs at activator binding sites instead. An inducer is needed to cause binding of the polymerase and activator protein. 9. What causes bacteria to fluoresce? What gene codes for this enzyme? The enzyme called lucipherase, coded for by the lux operon, causes bacteria to fluoresce.

10. What is a diauxic growth curve? Two exponential growth curves will occur, one from glucose, the preferred energy source, and then one from the second energy source. 11. Explain how catabolite repression depends on an activator protein. When glucose is used up, cyclic adenosine monophosphate, cAMP, levels increase. This binds to the cyclic AMP receptor protein, CRP, which controls transcription in catabolite repression. This is an activator protein that binds with the RNA polymerase to the promoter of the lac operon. 12. What are kinases and what is their role in two-component regulatory systems? Kinase add phosphate groups; sensor kinase, a protein in the cytoplasmic membrane, auto-phosphorylates and begins the feedback loop. The phosphate will bind to the response regulator, a protein in the cytoplasm, that will then bind to the DNA operator to regulate transcription. It may induce or repress an operon. 13. What are phosphatases and what is their role in two-component regulatory systems? Phosphatase is an enzyme that will close the feedback loop by removing the phosphate from the response regulator. 14. What advantage do quorum-sensing systems confer on bacterial cells? Quorum sensing allows bacteria to assess their population density. They can do this before initiating a response in case it needs a certain cell density to be effective, like in toxin production for pathogenic bacterium.

15. Why does attenuation control not occur in eukaryotes? Attenuation is control of transcription. The leader sequence on a DNA strand will code for a leader peptide. The leader peptide will include the product it is inhibiting, therefore if the cell has the product the leader protein will prevent it from making more. The structural genes that code for the product will not be transcribed and translated. Attenuation does not occur in eukaryotes as transcription and translation happen in different locations/organelles. 16. What is feedback inhibition? It is a mechanism to temporarily turn off the biosynthetic pathway, as the end product binds to the pathway’s first enzyme to change its shape, thus changing the shape of the active site. 17. What is the difference between an allosteric site and an active site? The allosteric site is where the end product binds on the enzyme, the active site is where the substrate binds to break or make a bond to continue biosynthesis. When the allosteric effector binds to the allosteric site, the substrate cannot bind to the active site. 18. What is an isoenzyme? Isoenzymes are different enzymes that code/catalyze the same reaction but require different end products as regulatory control. 19. What would happen to regulation from a promoter under negative control if the region where the regulatory protein binds was deleted? What if the promoter was under positive control? In negative control the absence of the region where the regulatory protein binds would allow the RNA polymerase to continue transcription. If the region was absent in positive control the regulatory protein could not bind and transcription would not be activated in the RNA polymerase....