Lecture 9 Enzymes-1 PDF

Faculty of Medicine Academic Year: 2024-2025 Year: 1 Semester: 1 Module: Human Body Function (HBF) 102  Enzymes I By: Dr. Sara Sayed Kadry Lecturer Medical Biochemistry & Molecular Biology, Faculty of Department: medicine,...

Faculty of Medicine Academic Year: 2024-2025 Year: 1 Semester: 1 Module: Human Body Function (HBF) 102  Enzymes I By: Dr. Sara Sayed Kadry Lecturer Medical Biochemistry & Molecular Biology, Faculty of Department: medicine, Cairo university 11/19/2024 22  Objectives 1. Define enzymes & recognize their medical importance. 2. Classify enzymes into six major groups. 3. Identify general properties of enzymes. 4. Describe mechanism of enzyme action. 5. Describe Factors affecting enzyme activity and reaction velocity 11/19/2024 HBF - 102 33  Introduction Enzyme : biocatalysts that regulate the rate of all biochemical reactions Substrate : molecule that enzymes work on , enzyme is specific to it Products : what the enzyme helps to produce from the reaction Active site : part of enzyme (cleft) that substrate molecule fits into, also called the catalytic site or substrate-binding site. 11/19/2024 HBF - 102 44  Introduction 11/19/2024 HBF - 102 55  Introduction 11/19/2024 HBF - 102 66  Introduction Enzymes are protein in nature Common features: All are produced by living cells and can act outside these cells. They are needed in very small amounts. They accelerate the reaction without affecting its equilibrium. They are not changed chemically by the end of the reaction. They show different degrees of specificity (act on a specific substrate or inter-related substrates). 11/19/2024 HBF - 102 77  Introduction Chemical nature: Most enzymes are protein in nature, either simple proteins or conjugated proteins. The conjugated protein is called ―Holoenzyme. The protein part is called “Apoenzyme”. The non-protein part is called “cofactor” to help in the reaction. 11/19/2024 HBF - 102 88  Introduction 11/19/2024 HBF - 102 99  Introduction Mechanism of Enzyme Action (induced fit model):  A substrate binds to an active site  change shape slightly, creating an ideal fit for catalysis  The enzyme lowers energy of activation (energy needed for the reaction to occur) 11/19/2024 HBF - 102 10 10  Introduction 11/19/2024 HBF - 102 11 11  Introduction 11/19/2024 HBF - 102 12 12  Introduction Factors Affecting The Rate Of Enzyme Catalyzed Reaction! 1- Substrate Concentration [S] 2- Enzyme Concentration (E) 3- Cofactor Concentration (C) 4- Inhibitor Concentration (I) 5- Temperature 6- pH 7- Time 11/19/2024 HBF - 102 13 13  Introduction 1. Substrate concentration:  The rate of enzyme-catalyzed reactions is directly proportional to the concentration of the enzyme-substrate complex  The velocity of the reaction increases as the substrate concentration [S] increases up to point where the enzyme is said to be saturated. 11/19/2024 HBF - 102 14 14  Introduction  The initial velocity (Vi ) increases to a maximum velocity (Vmax). “Michaelis-Menten curve” 11/19/2024 HBF - 102 15 15  Introduction 11/19/2024 HBF - 102 16 16  Introduction Michaelis constant or Km value  It is the substrate concentration that produces half the maximal velocity. 11/19/2024 HBF - 102 17 17  Introduction Significance:  Km determines the affinity between the enzyme & the substrate.  Smaller Km reflects higher affinity of the enzyme for its substrate.  Higher Km reflects lower affinity of the enzyme for its substrate. 11/19/2024 HBF - 102 18 18  Introduction 2. Enzyme concentration: The velocity of the reaction increases as the enzyme concentration increases up to a certain point. 11/19/2024 HBF - 102 19 19  Introduction 3. Cofactor concentration [C]: as the [C] increases the velocity of the reaction increases (directly proportional) up to a point. 11/19/2024 HBF - 102 20 20  Introduction 4. Inhibitor concentration [I]: The velocity of the reaction will be inversely proportional to the inhibitor concentration. 11/19/2024 HBF - 102 21 21  Introduction 5. Effect of temperature:  The rate of an enzymes catalyzed reaction increases by raising temperature !  The optimum temperature is at 37°C. 11/19/2024 HBF - 102 22 22  Introduction  At high temperature denaturation of the enzyme occurs. 11/19/2024 HBF - 102 23 23  Introduction 11/19/2024 HBF - 102 24 24  Introduction 6. Effect of pH: Any enzyme has an optimum pH, at which it acts maximally. The optimum pH of most enzymes is between 5 to 9. Activity decreases as we go away from the optimum pH. It stops about 2 units of pH above or below the optimum ph. 11/19/2024 HBF - 102 25 25  Introduction 11/19/2024 HBF - 102 26 26  Introduction 7. Time: By time the velocity of the reaction decreases as many substrates are converted to the reaction products, also by time the enzyme becomes inactive. 11/19/2024 HBF - 102 27 27  Introduction Biomedical importance: 1. Enzymes can be used as diagnostic markers to detect the presence of tissue specific disease. 2. Enzymes can be used as commercial diagnostic reagents in various biochemical estimations. 3. Enzymes can be used as therapeutic agents. 4. Enzymes can be target for certain drugs. 11/19/2024 HBF - 102 28 28  Introduction International classification of enzymes:  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. 11/19/2024 HBF - 102 29 29  Introduction 1. Oxido-reductases: Enzymes catalyzing oxidation reduction reactions 2. Transferases: Enzymes that catalyze the transfer of specific functional groups from one molecule to another. 11/19/2024 HBF - 102 30 30  Introduction 3. Hydrolases: Enzymes that catalyze bond cleavages by addition of water. 4. Lyases: Enzymes that catalyze the breaking of various chemical bonds without addition of water. 11/19/2024 HBF - 102 31 31  Introduction 5. Isomerases: Enzymes that catalyze structural rearrangement of a molecule. 11/19/2024 HBF - 102 32 32  Introduction 6. Ligases: Enzymes that are capable of catalyzing the reaction of joining two large molecules by establishing a new chemical bond. 11/19/2024 HBF - 102 33 33  Interactive Question Define enzyme ?? Enumerate three factors affecting enzyme activity ?? Explain: enzyme activity stops at 70 degrees C ?? 11/19/2024 HBF - 102 34 34  Interactive Question 1. Enzymes accelerate reactions by ____________the activation energy needed for the reaction. a) Stopping b) Raising c) Lowering d) binding 11/19/2024 HBF - 102 35 35  Interactive Question 2- An enzyme is a …… a) Carbohydrate b) Lipid c) Protein d) Nucleic acid 11/19/2024 HBF - 102 36 36  Interactive Question 3- The optimum pH of most of the enzymes is …….. a) Between 2 and 4 b) Between 5 and 9 c) Between 8 and 12 d) Above 12 11/19/2024 HBF - 102 37 37  Summary Enzymes are biocatalysts that regulate the rate of all biochemical reactions. They are protein in nature, having common features. Many factors influence the rate of enzyme-catalyzed reaction such as substrate concentration and temperature. Enzymes are classified into six major classes. 11/19/2024 HBF - 102 38 38  References 11/19/2024 HBF - 102 39 39