Enzyme 1.pptx PDF

BASIC ENZYMOLOGY D r. Zahraa K. Mohammed  The student can be able to: 1. Define enzymes. 2. List the property of enzymes. 3. Demonstrate the different types of enzyme specificity with example. 4. Explain the mechanism of action of enzymes. 1. Classify enzymes with example. 3. Define differen...

BASIC ENZYMOLOGY D r. Zahraa K. Mohammed  The student can be able to: 1. Define enzymes. 2. List the property of enzymes. 3. Demonstrate the different types of enzyme specificity with example. 4. Explain the mechanism of action of enzymes. 1. Classify enzymes with example. 3. Define different glossary as: cofactor, coenzyme, holoenzyme, etc 4. Define Isoenzymes. 5. Name some group transferring Coenzymes. 6. Explain enzyme activities indicating various methods for their determinations. 1. Define the active site of enzyme. 2. Enumerate the salient features of the active site. 3. Express the relation between enzyme and activation energy. 1. Discuss the different factors influencing enzyme activity. 2. Illustrate the effect of substrate concentration on enzyme velocity reaction. 3. Describe Michaelis-Menten equation and its application in enzyme kinetics 4. Define km value. 1. Review different types of enzyme inhibition with examples. 2. Discuss with diagram and example the competitive and non-competitive enzyme inhibition. 3. State the clinical importance of competitive and non-competitive enzyme inhibition. 4. Compare among different types of enzymatic inhibition mechanism. 5. Explain feed-back inhibition. 6. Describe suicide inhibition with example. 7. Define allosteric inhibition, features and mechanism with examples. 1. Explain the mechanism of allosteric regulation 2. Define induction and repression, with example. ENZYME Virtually all reactions in the body are mediated by enzymes, which are protein catalysts that increase the rate of reactions without being changed in the overall process. Among the many biologic reactions that are energetically possible, enzymes selectively channel reactants (called substrates) into useful pathway PROPERTIES OF ENZYMES A. A ctive sites Enzyme molecules contain a special pocket or cleft called the active site.The active site contains amino acid side chains that participate in substrate binding and catalysis.The substrate binds the enzyme, forming an enzyme–substrate (ES) complex. Binding is thought to cause a conformational change in the enzyme (induced fit) that allows catalysis. ES is converted to an enzyme–product (EP) complex that subsequently dissociates to enzyme and product. E +S ES EP E +P B. C atalytic efficiency Enzyme-catalyzed reactions are highly efficient faster than uncatalyzed reactions.The number of molecules of substrate converted to product per enzyme molecule per second is called the turnover number, or kcat. C. Specificity Enzymes are highly specific, interacting with one or a few substrates and catalyzing only one type of chemical reaction. [Note:The set of enzymes made in a cell determines which metabolic pathways occur in that cell.] PROPERTIES OF ENZYMES D. Holoenzymes Some enzymes require molecules other than proteins for enzymic activity.The term holoenzyme refers to the active enzyme with its nonprotein component, whereas the enzyme without its nonprotein moiety is termed an apoenzyme and is inactive. the nonprotein moiety is called a cofactor and if its a metal ion such as Zn2+ or Fe2+, it is called prosthetic group and If it is a small organic molecule, it is termed a coenzyme. Coenzymes frequently are derived from vitamins. For example, NAD+ contains niacin and FAD contains riboflavin. PROPERTIES OF ENZYMES E. Regulation Enzyme activity can be regulated, that is, increased or decreased, so that the rate of product formation responds to cellular need. F. Location within the cell Many enzymes are localized in specific organelles within the cell. Such compartment serves to isolate the reaction substrate or product from other competing reactions.This provides a favorable environment for the reaction, and organizes the thousands of enzymes present in the cell into purposeful pathways ENZYMES CLASSIFIC ATION According to the International Union of Biochemists (I U B), enzymes are divided into six functional classes and are classified based on the type of reaction in which they are used to catalyze.The six kinds of enzymes are hydrolases, oxidoreductases, lyases, transferases, ligases and isomerases.  HOW ENZYME CATALYSE A REACTION? Enzymes are catalyst that accelerate the rate of biochemical reaction by decreasing the energy of activation. Every chemical reaction have energy barrier that must be crossed by the reactant molecules in order to convert itself into the product. The amount of energy supplied to reactant molecules in order to cross the energy barrier to from product is known as Energy of activation. If energy of activation is higher, rate of reaction is slower and if it is lower, the rate of reaction is faster. The role of enzyme in biochemical reaction is to reduce the amount of energy of activation such that the rate of reaction increases. During enzyme catalysis, active site of enzyme binds with substrate molecules to form Enzyme- substrate (ES) complex. During this binding some binding energy is released which is utilized to activate the substrate (reactant) molecules to form product. Thus the requirement of the amount of activation energy is decreased such that rate of reaction increases. The amount of activation decrease is equal to the amount of binding energy released during binding of enzyme and substrate.  RATE OF ENZYME REACTIONS ◾ The rate of enzyme reaction is measured by the amount of substrate changed or amount of product formed during a period of time. ◾ If enzyme activity is measured over a period of time, the rate of reaction usually falls, most commonly as a result of a fall in the substrate concentration. FACTORS AFFECTIN G THE RATE OF ENZYME REACTIONS TEMPERATUR E Temperature: Raising temperature generally speeds up a reaction, and lowering temperature slows down a reaction. However, extreme high temperatures can cause an enzyme to lose its shape (denature) and stop working. PH pH: Each enzyme has an optimum pH range. Changing the pH outside of this range will slow enzyme activity. Extreme pH values can cause enzymes to denature. ENZYME CONCENTRATION Enzyme concentration: Increasing enzyme concentration will speed up the reaction, as long as there is substrate available to bind to. Once all of the substrate is bound, the reaction will no longer speed up, since there will be nothing for additional enzymes to bind to. FACTORS AFFECTING ENZYME ACTIVITY activator - substances that bind to allosteric sites and keep the enzymes in their active configurations Inhibitors -are chemicals that reduce the rate of enzymic reactions. They are usually specific and they work at low concentrations. They block the enzyme but they do not usually destroy it. Many drugs and poisons are inhibitors of enzymes in the nervous system MICHAELIS-MENTEN theory A. Reaction model Leonor Michaelis and Maude Menten proposed a simple model that accounts for most of the features of enzyme-catalyzed reactions. In this model, the enzyme reversibly combines with its substrate to form an ES complex that subsequently yields product, regenerating the free enzyme.The model, involving one substrate molecule, is represented below: where S is the substrate E is the enzyme ES is the enzyme–substrate complex P is the product k1, k-1, and k2 are rate constants  Important conclusions about Michaelis-Menten kinetics 1. Characteristics of Km: Km—the Michaelis constant—is characteristic of an enzyme and its particular substrate, and reflects the affinity of the enzyme for that substrate. Km is numerically equal to the substrate concentration at which the reaction velocity is equal to 1 ⁄2Vmax. Km does not vary with the concentration of enzyme. a. Small Km: A numerically small (low) Km reflects a high affinity of the enzyme for substrate, because a low concentration of substrate is needed to half-saturate the enzyme—that is, to reach a velocity that is 1 ⁄2Vmax (Figure ). b. Large Km: A numerically large (high) Km reflects a low affinity of enzyme for substrate because a high concentration of substrate is needed to half-saturate the enzyme LINEWEAVER-BURK PLOT it is not always possible to determine when Vmax has been achieved, because of the gradual upward slope of the hyperbolic curve at high substrate concentrations. However, if 1/vo is plotted versus 1/[S], a straight line is obtained.This plot, the Lineweaver-Burk plot (also called a double-reciprocal plot) can be used to calculate Km and Vmax, as well as to determine the mechanism of action of enzyme inhibitors. 1.The equation describing the Lineweaver-Burk plot is where the intercept on the x-axis is equal to −1/Km, and the intercept on the y- axis is equal to 1/V LINEWEAVER-BURK PLOT. INHIBITION O F ENZYME ACTIVITY Any substance that can diminish the velocity of an enzyme-catalyzed reaction is called an inhibitor. In general, irreversible inhibitors bind to enzymes through covalent bonds. Reversible inhibitors typically bind to enzymes through noncovalent bonds,. The two most commonly types of reversible inhibition are competitive and noncompetitive.  The two most commonly encountered types of reversible inhibition are competitive (which increases the apparent Km) and noncompetitive (which decreases the apparent Vmax). A. EFFECT OF A COMPETITIVE INHIBITOR O N THE REACTION VELOCITY (VO) VERSUS SUBSTRATE ([S]) PLOT. B. LINEWEAVER-BURK PLOT OF COMPETITIVE INHIBITION OF A N ENZYME. A. EFFECT O F A N O N C O M P E T I T I V E INHIBITOR O N TH E R E A C T I O N V ELO CI TY (VO) VERSUS SUBSTRATE ([S]) PLOT. B. LINEWEAVER- BURK PLOT O F N O N C O M PETITIVE IN H IBITIO N O F A N EN Z Y M E. REGULATIO N O F ENZYME ACTIVITY A. Regulation of allosteric enzymes Allosteric enzymes are regulated by molecules called effectors (also called modifiers) that bind noncovalently at a site other than the active site.These enzymes are usually composed of multiple subunits, and the regulatory (allosteric) site that binds the effector may be located on a subunit that is not itself catalytic. The presence of an allosteric effector can alter the affinity of the enzyme for its substrate, or modify the maximal catalytic activity of the enzyme, or both. Effectors that inhibit enzyme activity are termed negative effectors, whereas those that increase enzyme activity are called positive effectors. Allosteric enzymes frequently catalyze the committed step early in a pathway. B. REGULATION OF ENZYMES BY COVALENT MODIFICATION Many enzymes may be regulated by covalent modification, most frequently by the addition or removal of phosphate groups from specific serine, threonine, or tyrosine residues of the enzyme. Protein phosphorylation is recognized as one of the primary ways in which cellular processes are regulated