Enzymes 3: An Overview

Enzymes 3 Enzyme regulation Regulatory enzymes E1 E2 E3 A B C D In cell metabolism, group of enzymes work together in a sequential pathway. The reaction p...

Enzymes 3 Enzyme regulation Regulatory enzymes E1 E2 E3 A B C D In cell metabolism, group of enzymes work together in a sequential pathway. The reaction product of E1 will be the substrate for the next ENZ & so on. Regulatory enzymes E1 E2 E3 A B C D Regulatory enzyme adjust the overall rate of the Usually irreversible pathway to meet the cell‘s demand KEY ENZYME Rate limiting enzyme REGULATORY ENZYME Control of the metabolic Key enzymes pathway Regulatory enzymes Rate limiting enzymes  Enzyme regulation ENZYME ENZYME CATALYTIC QUANTITY ACTIVITY (long term regulation) (short term regulation) takes hours to days) takes second to minutes  Long Term Regulation LONG TERM REGULATION occurs by controlling the number or the concentration of enzyme molecules present. Controlling the number of the (Gene level))Slow in enzyme molecules present, determined the human, occurring by the rate of over hours to days synthesis & rate of degradation of the enzyme protein [Enzyme turnover] Regulation of enzyme quantity Enzyme quantity Enzyme Enzyme synthesis at degradation gene level Induction Repression 1-Regulation of enzyme synthesis  A- Induction Stimulation of Enzyme Synthesis (increase the rate of transcription) by an inducer, usually the substrate or a hormone B- Repression Inhibition of Enzyme Synthesis (decrease the rate of transcription) in response to a repressor, the product or a hormone  Regulation of enzyme degradation Absence of Alter the Enzyme more substrate, enzyme susceptible to coenzymes conformation proteolysis What is meant by induction of an enzyme? A. Increased synthesis of the enzyme from its gene. B. Increased kinetic energy of the enzyme. C. Conformational change leading to activation of the enzyme. D. Enhanced affinity of the enzyme to its substrate. E. Activation of an inactive enzyme. Regulation of catalytic activities (short term regulation) Mechanisms of Regulation of catalytic activities 2. REVERSIBLE 1.ALLOSTERIC COVALENT REGULATION MODIFICATION 3.Irreversible covalent modification 1-Allosteric Regulation (Allos= another site) Active site Allosteric Allosteric site bind to bind to Enzyme substrate allosteric modifier Allosteric Regulation Allosteric enzymes have 2 binding sites: 2-Allosteric site 1-Active site binds regulator binds substrate (Effectors or modifiers) Allosteric Regulation Binding of regulatory molecule to allosteric site by non-covalent bonds. It induces a conformational change in the enzyme Increase the enzyme Inhibit the enzyme activity(positive activity(negative allosteric modifier ) allosteric modifier Feed- Back Inhibition E1 E2 E3 A B C D When end product binds the allosteric site, it makes conformational Accumulation of Allosteric inhibition change in the end products of first enzyme enzyme, so that the active site is NOT fitted for substrate An allosteric molecule is characterized by: A. Can bind covalently to the enzyme. B. Can bind to the active site of the enzyme. C. Binds non covalently to the enzyme. D. It is derived from a vitamin. 2-Reversible Covalent modification 2-Reversible Covalent modification 1-Phosphorylation/ 2-Methylation/ Dephosphorylation demethylation (Most commonly used) 3-Acetylation/ deacetylation  Phosphorylation Ser Thr Tyr (His) OH Kinase P phosphorylation Conformational Protein dephosphorylastion Change Phosphatase Glycogen phosphorylase b Glycogen phosphorylase a Inactive Active  3-Irreversible covalent modification (proteolytic cleavage) Cleavage of small peptide Reveal the catalytic site (inactive zymogen) (active enzyme) 3-Proenzyme examples Digestive enzymes to protect the cells producing them e.g. pancreas from autodigestion Q:Explain why pancreatic enzymes are released in the form of zymogens ANSWER