University:
Glendale Community College
Course:
BIO160 | Introduction to Human Anatomy and Physiology
Academic year:

2020
Views:

91

Pages:

7
Author:

unidosenluz0y

Section 6.5: Enzyme Regulation Figure 6.20 Alcohol Dehydrogenase §Alcohol Dehydrogenase—catalyzes the reversible oxidation of alcohols to aldehydes or ketones §Requires Zn+2, Cys 48, Cys 174, His 67 §Uses NAD+ as a hydride (H:-) ion acceptor Section 6.5: Enzyme Regulation §Enzyme regulation is necessary for: §Maintenance of ordered state – timely production of substances §Conservation of energy – acquire nutrients to meet energy needs §Responsiveness to environmental changes – increase/decrease in rates in response to environmental changes §Four methods of control §genetic control - – synthesis in response to changing metabolic needs §covalent modification (e.g. phosphorylation) – interconversion between active/inactive forms §allosteric regulation – binding of effectors §compartmentation – physical separation of processes Section 6.5: Enzyme Regulation §Genetic Control §Happens at the DNA level; repression or induction of enzyme synthesis §Covalent Modification §Regulation – active to inactive form §Types -phosphorylation, methylation, acetylation, nucleotidylation §Inactive precursors - stored as proenzymes or zymogens Figure 6.21 The Activation of Chymotrypsinogen Section 6.5: Enzyme Regulation §Allosteric Regulation Figure 6.22 The Rate of an Enzyme-Catalyzed Reaction as a Function of Substrate Concentration §Regulated by the binding of effectors at allosteric sites §Sigmoidal curve indicates §If effectors are substrates, then it is homotropic §If the ligand is different, then it is heterotropic Section 6.5: Enzyme Regulation Figure 6.23a Allosteric Interaction Models §Most allosteric enzymes are multisubunit enzymes §Shift between conformations: T (taut) low binding; R (relaxed) tight binding §Concerted model, all subunits are changed at once from taut (T) to relaxed (R) or vice versa §Activator shifts the equilibrium in favor of the R form; inhibitor shifts in favor of the T form §Supported by positive cooperativity where binding of one ligand increases subsequent binding §It is not supported by negative cooperativity Section 6.5: Enzyme Regulation Figure 6.23 Allosteric Interaction Models §Sequential model binding of the ligand to one subunit §Triggers a conformational change - passed to subsequent subunits §More complex model that allows for intermediate formations §Accounts for both positive and negative cooperativity §Neither model perfectly accounts for all enzyme behavior Section 6.5: Enzyme Regulation §Compartmentation - Compartments created by cellular infrastructure regulate biochemical reactions §Physical separation makes separate control possible §Solves several problems: §Divide and control – coordinated regulation preventing wasteful dissipation of resources §Diffusion barriers – microenvironments to concentrate both E and S §Specialized reaction conditions – environments with unique properties; low pH for hydrolytic reactions §Damage control – segregation of toxic reaction products protects other cellular components