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UB BIO 201 - Enzyme Regulation

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Bio 201 1st Edition Lecture 19 Outline of Last Lecture . Spontaneous?II. CatalystsIII. EnzymesA. Inducing FitB. How enzymes work1. Orientation2. Strain3. Chemistry C. Mutation and Human DiseasesOutline of Current LectureI. RegulationA. Mechanisms of RegulationII. Feedback InhibitionA. End-product inhibitionB. Direct Feedback inhibitionC. Principles of Regulation Current LectureI.Regulation- Maintains appropriate levels of all cellular compounds, ensures that compounds are available when needed, prevents toxic build-up. These 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.A. Mechanisms of Regulation:1. Competitive Inhibition- Compound binds at active site of enzyme, preventing substrate binding. Inhibiting only, usually reversible. Often a non-native molecule such as a toxins or medicines. Irreversible competitive inhibition does not happen often but when it does, it’s because a toxin bonds covalently to the active site. 2. Allosteric Regulation- Activating or inhibiting. Binds to other site than active site, this alters the active site through a conformational change. -Activation- Allosteric activator binds to allosteric site resulting in a conformational changeat the active site that allows the substrate to bind-Inhibition- Non- competitive inhibitor binds somewhere other than active site, causing a conformational change in active site that prevents substrate from binding or decreases therate of catalysis. 3. Covalent Modification- Most common type of this is phosphorylation. This can be activating or inhibiting. Covalent modification as a mode of enzyme regulation is reversible, dephosphorylation. 4. Zymogen Activation- Irreversible, and only activating. Zymogen is the enzyme precursor,it is cleaved into 2 or more pieces by hydrolysis (by a protease) One piece is the active enzyme. This is used in cases where active enzyme could be detrimental to the cell-Activation by pH- low pH stomach alters conformation of pepsin, activating hydrolysis. Hydrolysis removes “masking sequence” which reveals active site of protein for hydrolysis of other proteins. Wrong pH or masking sequence present, cannot act. -Activation by Proteases- Typsinogen and other zymogens released into duodenum by pancreas. Enterokinase in duodenum catalyzes trypsinogen trypsin. Trypsin cleaves remaining pancreatic zymogens active site. Active enzymes break down remaining food particles for absorption by small intestine. II. Feedback Inhibition- Ensures that the reaction stops when enough product has been produced to satisfy the needs of the cell. This prevents depletion of reactants when they are needed for other pathways. A. End-product inhibition- Usually, always allosteric. Cell produces only as much product as necessary, substrate 1 which may be used in other pathways in consumed. Thisensures that the levels of intermediate- which at best are useless or at worst, toxic- remain low. B. Direct Feedback inhibition- If product is similar to the enzyme substrate, it may bind to the active site ( comp. inhibition), if not, it must use allosteric inhibition. Cell producesonly as much product as necessary, substrate may be used in other pathways and is consumed. C. Principles of Regulation- Regulations involved in irreversible reactions, feedback inhibition of the earliest enzyme in the pathway that is unique to the product, feedback using the product of whose levels are most important to maintain or


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