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Tuesday, May 23, 2017 Unit 1: Enzymes and the digestive system Title: Enzyme action Keywords: • activation energy • lock and key model Learning Objectives: • induced fit model We are learning…. • How do enzymes speed up chemical reactions? • How does the structure of enzyme molecules relate to their function? • What is the lock and key model of enzyme action? • What is the induced-fit model of enzyme action? Starter: Write down five things you know about enzymes. What’s wrong with these statements? 1. Enzymes are biological catalysts which change the rate of chemical reactions by increasing activation energy. 2. Enzymes are used up during reactions. 3. Enzymes are fibrous proteins made up of amino acids joined by glycosidic bonds. 4. Each enzyme catalyses many different reactions. 5. Substrates bind with enzymes at the substrate site, forming a product. 6. Catabolic enzymes build up molecules and anabolic enzymes break larger molecules into smaller ones. 2.5 Enzymes Essential idea: Enzymes control the metabolism of the cell. Nature of science: • Experimental design—accurate, quantitative measurements in enzyme experiments require replicates to ensure reliability. 2.5 Enzymes Understandings: • Enzymes have an active site to which specific substrates bind. • Enzyme catalysis involves molecular motion and the collision of substrates with the active site. • Temperature, pH and substrate concentration affect the rate of activity of enzymes. • Enzymes can be denatured. 2.5 Enzymes Applications and skills: • Application: Methods of production of lactose-free milk and its advantages. • Skill: Design of experiments to test the effect of temperature, pH and substrate concentration on the activity of enzymes. • Skill: Experimental investigation of a factor affecting enzyme activity. (Practical 3) 2.5 Enzymes Guidance: • Lactase can be immobilized in alginate beads and experiments can then be carried out in which the lactose in milk is hydrolysed. • Students should be able to sketch graphs to show the expected effects of temperature, pH and substrate concentration on the activity of enzymes. • They should be able to explain the patterns or trends apparent in these graphs. 2.5 Enzymes Theory of knowledge: • Development of some techniques benefits particular human populations more than others. For example, the development of lactose-free milk available in Europe and North America would have greater benefit in Africa/ Asia where lactose intolerance is more prevalent. The development of techniques requires financial investment. Should knowledge be shared when techniques developed in one part of the world are more applicable in another? Utilization: • Enzymes are extensively used in industry for the production of items from fruit juice to washing powder. 8.1 Metabolism HL only Essential idea: Metabolic reactions are regulated in response to the cell’s needs. Nature of science: Developments in scientific research follow improvements in computing—developments in bioinformatics, such as the interrogation of databases, have facilitated research into metabolic pathways. 8.1 Metabolism HL only Understandings: • Metabolic pathways consist of chains and cycles of enzyme-catalysed reactions. • Enzymes lower the activation energy of the chemical reactions that they catalyse. • Enzyme inhibitors can be competitive or noncompetitive. • Metabolic pathways can be controlled by end-product inhibition. 8.1 Metabolism HL only Applications and skills: • Application: End-product inhibition of the pathway that converts threonine to isoleucine. • Application: Use of databases to identify potential new anti-malarial drugs. • Skill: Calculating and plotting rates of reaction from raw experimental results. • Skill: Distinguishing different types of inhibition from graphs at specified substrate concentration. 8.1 Metabolism HL only Guidance: • Enzyme inhibition should be studied using one specific example for competitive and non-competitive inhibition. 8.1 Metabolism HL only Theory of knowledge: • Many metabolic pathways have been described following a series of carefully controlled and repeated experiments. To what degree can looking at component parts give us knowledge of the whole? Utilization: • Many enzyme inhibitors have been used in medicine. For example ethanol has been used to act as a competitive inhibitor for antifreeze poisoning. • Fomepizole, which is an inhibitor of alcohol dehydrogenase, has also been used for antifreeze poisoning. 8.1 Metabolism HL only Aims: • Aim 6: Experiments on enzyme inhibition can be performed. • Aim 7: Computer simulations on enzyme action including metabolic inhibition are available. Explain the diagram to the person next to you Use these keywords to help you: Substrate, active site, enzyme-substrate complex, reactants, products, protein, pH, temperature, collisions, hydrolysis What are enzymes? Enzymes are biological catalysts. They make chemical reactions go faster but don’t actually take part in the reaction. They do this by reducing the activation energy required to initiate the reaction. What is activation energy? HL only Before any chemical reaction can proceed it must initially be activated, i.e. its energy must be increased. The energy required is called activation energy. Once provided, the activation energy allows the products to be formed. How do enzymes lower activation energy? HL only Heat is often the source of activation energy and enzymes often dispense with the need for this heat and so allow reactions to take place at lower temperatures. Enzymes provide a platform for the reactants of a reaction to come together at the active site. Without enzymes, more energy would be required in order for reactants molecules to collide with one another. When a chemical reaction involves two or more reactants, the enzyme provides a site where the reactants are positioned very close to each other and in an orientation that facilitates the formation of new covalent bonds. How do enzymes work? Enzymes are globular proteins. Proteins are made from chains of amino acids joined by peptide bonds. Each type of enzyme catalyses a specific reaction. The important part of the enzyme is the active site. The substrate fits into this part, and an enzyme-substrate complex is formed. How are the products of enzyme catalysed reactions produced? Once the substrate binds with the active site of the enzyme and forms an enzyme-substrate complex, a reaction occurs and the product is released, leaving the enzyme free to process another substrate molecule. Enzymes are able to process hundreds of molecules. The lock and key model of enzyme action Enzymes are highly specific in the reactions catalysed. Some enzymes catalyse the transformation of one particular type of substrate molecule or, at most, a very restricted group of substrate molecules. Some catalyse only one type of chemical change. The specificity of enzymes is due to the configuration of the active site. In the lock and key model, the substrate is the ‘key’ that fits exactly into the enzyme ‘lock’ The induced fit model of enzyme action Evidence from protein chemistry suggests that a small rearrangement of chemical groups occurs in both the enzyme and the substrate molecules when the enzymesubstrate complex is formed. This is called induced fit. The induced fit theory can be compared to a hand entering a glove. The hand will move slightly to fit into the glove, while the gloves’ shape will change to accommodate the hand. Main activity: Using the mini white-boards and working with a partner…. One person explains the induced-fit model of enzyme action The other person explains the lock and key model of enzyme action. Use diagrams and keywords from the lesson and reference activation energy in your explanation. Anabolic and catabolic enzymes Anabolic enzymes facilitate reactions that take simple molecules and join them together to form complex molecules. For example, glucose molecules go through a condensation reaction forming many glycosidic bonds between molecules and eventually forming the polysaccharide starch. Many enzymes are involved in this process, including starch synthase. Catabolic enzymes break larger molecules into smaller ones. Amylase will hydrolyse the glycosidic bonds in a starch molecule to produce glucose. Main Activity: Complete the worksheet ‘enzymes’ How successful were we this lesson? Learning Objective We were learning…..