Enzymes 2 PDF

ENZYMES 2 Sahar Abdelmoneim learning objectives: Explain how enzyme increase the velocity of the reaction Explain the properties of enzymes How enzymes work Factors affecting reaction velocity (enzymes activity) Identify enzymes as biological catalysts.  How enzyme increase the vel...

ENZYMES 2 Sahar Abdelmoneim learning objectives: Explain how enzyme increase the velocity of the reaction Explain the properties of enzymes How enzymes work Factors affecting reaction velocity (enzymes activity) Identify enzymes as biological catalysts.  How enzyme increase the velocity of the reaction Enzyme lower the activation energy.  Factors affecting reaction velocity (enzymes activity) 1. Substrate concentration 2. Enzyme concentration 3. pH 4. Temperature 5. Inhibitors  Substrate concentration Increase in substrate concentration leads to increase in the velocity of reaction But it reaches a saturation point when all the enzyme molecules are occupied Vmax Reaction velocity Substrate concentration  Enzyme concentration Increase in the enzyme concentration leads to increase in the velocity of reaction  pH The concentration of H+ affects reaction velocity in several ways Effect on the ionization of the active site. Effect on enzyme denaturation Optimum pH varies with different enzymes e.g., pepsin has an optimum pH 2, whereas most enzymes are designed to work at neutral pH. pH Temperature  Inhibition of enzyme activity Any substance that can decrease the velocity of an enzyme-catalyzed reaction is called an inhibitor.  Types of inhibitors: Reversible inhibitors Irreversible inhibitors Bind to enzymes through Bind to enzymes through covalent noncovalent bonds. bonds Can be washed out of the solution Cannot be washed out of the of enzyme by dialysis solution of enzyme by dialysis Nonpoisons Poisons Drugs lead (pb) and cyanide (CN).  Reversible inhibitors Competitive inhibition Noncompetitive inhibition Structurally similar to the substrate Has no similarity to the substrate Binds at the active site structure. Binds at a site other than the active site  IMPORTANT TEARMS Allosteric enzymes Are enzymes whose activity at the catalytic site may be modulated by the presence of allosteric effectors (small molecules) at an allosteric site allosteric effectors cause a conformational change in the enzyme so that the affinity for the substrate or other ligands also change. If the effector causes an increase in enzyme activity it is called positive allosteric effector, in case it lowers the activity it is referred to as a negative allosteric effector  IMPORTANT TEARMS Isoenzymes Are enzymes that catalyze the same reaction but differ in their structure. e.g., of isozymes of wide clinical application are lactate dehydrogenase (LDH), creatine kinase (CK) and alkaline phosphatase ❑In cells most reactions are catalyzed by enzymes, which are regenerated during the course of a reaction. ❑These biological catalysts are important because they speed up the rates of reactions that would otherwise be too slow to support life. ❑Enzymes increase reaction rates by as much as thousand fold. 16 THANKS