Title Biology_IX_6_Review Questions.pdf ✅

ClassNotes Understanding the Concepts Q#1 How would you define enzymes? Describe their characteristics. Ans: Enzymes: Proteins which speed of chemical reactions inside living organisms, by minimizing the activation energy are known as enzymes. Functions of Enzymes: Enzymes are proteins that catalyze i.e. speed up) biochemical reactions and are not changed during the reaction. In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into different molecules, the products. Almost all processes in a cell need enzymes in order to occur at significant rates. Characteristics of Enzymes: 1. Almost all enzymes are proteins i.e. they are made of amino acids. 2. Most enzyme reaction rates are millions of times faster than those of comparable un-catalyzed reactions. As with all catalysts, enzymes are not consumed by the reactions they catalyze. 3. Enzymes are usually very specific for the type of reaction and for the nature of their substrates 4. The activities of enzymes are determined by a small portion of the enzyme molecule (around 34 amino acids) which is directly involved in catalysis. This catalytic region, known as the active site, recognizes and binds the substrate, and then carries out the reaction. www.classnotes.xyz Biology ClassNotes, Inc. © 2020 1
ClassNotes 5. Since enzymes are extremely selective for their substrates and speed up only a few reactions, the set of enzymes made in a cell determines which metabolic pathways occur in that cell. 6. Enzymes can be categorized on the basis of the site where they work i.e. they may be intracellular enzymes (e.g. enzymes of glycolysis working in the cytoplasm) or may be extracellular enzymes (e.g. pepsin enzyme working in the stomach cavity). 7. The enzyme activity is controlled in the cell by many ways. Enzyme production can be enhanced or diminished by a cell in response to changes in the cell's environment. Enzyme activity can also be regulated by inhibitors and activators. 8. Some enzymes do not need any additional components to show full activity However, others require non-protein molecules or ions called cofactors for activity. Types of Cofactors: Cofactors can be either inorganic (e.g. metal ions) or organic (e.g. flavin and heme). Coenzymes: If organic cofactors are tightly bound to enzyme, they are called prosthetic groups, but if they are loosely attached with enzyme, they are called coenzymes. Coenzymes are small organic molecules that transport chemical groups from one enzyme to another. Some important coenzymes are vitamins (e.g. riboflavin, thiamine and folic acid). 9. Several enzymes can work together in a specific order, creating metabolic pathways. In a metabolic pathway, one enzyme takes the product of another enzyme as a substrate. After the catalytic reaction, the product is then passed on to another enzyme. www.classnotes.xyz Biology ClassNotes, Inc. © 2020 2
ClassNotes Q#2 What do you mean by activation energy and why it is referred in the definition of enzymes? Ans: Activation Energy: The minimum amount of energy required for an effective collusion during a chemical reaction is called activation energy. Significance of Activation Energy: All chemical reactions require activation energy to break chemical bonds and begin the reaction. The need for activation energy acts as a barrier to the beginning of reaction. Reference of Activation Energy in Enzymes: Enzymes lower such barriers by decreasing the requirement of activation energy of enzymes, reactions proceed at a faster rate Enzymes lower the activation energy Enzymes lower the activation energy in several ways. They do so by: i. Altering the shape of the substrates and reducing the amount of energy required to complete the transition. ii. Disrupting the charge distribution. iii. Bringing substrate in the correct orientation to react. Q#3 In a range of 0-35°C, the rate of reaction of an enzyme is proportional to temperature. Above 35°C and below 0°C Enzyme activity slows down and eventually stops. Explain why? Ans: Increases in temperature will speed up the rate of enzyme catalyzed reactions, but only to a certain limit. Optimum Temperature: Every enzyme works at its maximum rate at a specific temperature called as the optimum temperature for that enzyme. When temperature rises to a certain www.classnotes.xyz Biology ClassNotes, Inc. © 2020 3
ClassNotes limit, the heat adds in the activation energy and also provides kinetic energy and so reactions are accelerated. Denaturation of Enzyme: When temperature is raised well above the optimum temperature, the heat energy increases the vibrations of atoms of enzyme molecules and the globular structure of enzyme is lost. This is known as denaturation of enzyme. It results in a rapid decrease in the rate of enzyme action and it may be blocked completely. Conclusion: Thus above 35°C and below 0°C Enzyme activity slows down and eventually stops. Q#4 How does pH affect enzyme activity? pH: All enzymes work at their maximum rate at a narrow range of pH, called as the optimum pH. A slight change (increase or decrease) in this pH causes retardation in enzyme activity or blocks it completely. Every enzyme has its specific optimum pH value. www.classnotes.xyz Biology ClassNotes, Inc. © 2020 4