BIOLOGY 207 1st Edition Lecture 10 Outline of Previous Lecture I. Nature of virusesII. Lytic vs. LysogenicOutline of Current Lecture I. Negative ControlII. Positive ControlCurrent LectureMetabolic Regulation 1I. Negative Controla. Repression i. Affects anabolic enzymes (enzymes that build up)ii. Happens because cells want to conserve energy and not waste on what they don’t have to1. Don’t turn on enzymes needed to make a resource if it is already present in the environment; repress the enzyme to avoid wasting energy2. Excess of the substance in the environment causes gene expression to be repressedThese 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.b. Induction i. Affects catabolic enzymes (enzymes that break things down)ii. Occurs because cells want to be able to use the resources available to themiii. If a substrate is present, even if it is not the preferred enzyme for the cell, the enzyme is turned on to break it downiv. Substrate presence causes induction of catabolic enzymes c. Repressor proteinsi. Both induction and repression use repressor proteinsii. Negative control indicates repressor proteins (for both repression and induction)iii. Effector molecules determine the mechanism for negative control1.1. Inducers:Causes repressor to fall off the DNA2. Corepressors:Causes repressor to bind DNAiv. Repressor protein is allosteric- conformation changes when an effector binds to it; causes it to bind (or not bind) to the DNA1. Binds to the operator region of the DNA (NOT the promoter)II. Positive Controla. Activationi. Activator proteins needed for RNA polymerase bindingii. Positively controlled operons have RNA polymerase that bind in the promoter weakly1. Poor matches to the consensus sequence2. RNA polymerase can’t bind to these promoters well without help3. Activator protein has this role:a. Modify the structure of the DNA to aid in the binding of the RNA polymeraseb. Interact directly with RNA polymerase to facilitate bindingiii. Whereas negative control requires a repressor protein, positive control involves an activator proteinIII. Global Control: the lac operona. Distinction between operon and reguloni. Operon: group of genes that are coordinately regulated and transcribed togetherii. Regulon: group of operons under control of a single regulatory proteiniii. Regulatory protein can be either an activator or a repressorb. Global controli. cells must respond to environmental changesii. response that typically involves regulation of many genes1. this sort of regulation is called the global control systemc. Example: Catabolite repressioni. Controls which carbon source is usedii. Enzymes needed to break down the preferred carbon source are synthesized if the source is present; enzymes used to break down alternate carbon sources are repressed if the preferred source is presentiii. Considered as global control because several operons are used1. Diauxic growthd. lac operoni. encodes enzymes needed for utilizing lactoseii. lacY encodes a permease which transports lactose into the celliii. lacZ encodes a beta-galactosidase which breaks lactose down into glucoseand galactoseiv. lactose involves both positive and negative control1. the lac operon provides the negative control2. positive control occurs through:a. glucose inhibits synthesis of regulatory nucleotide called cyclic AMPi. activator protein for lactose utilization is called CRP (cyclic AMP receptor protein)b. CRP won’t bind to the lac promoter uncless cyclic AMP binds to itc. CRP acts as an activator, making this a case of positive control3. What determines if lactose is used:a. CyclicAMP levels are high enough to cause CRP to bind to the promoter and recruit RNA polymerase b. Inducer (allolactose) is present, causing repressor protein to fall off the