Enzymes Laboratory 4IntroductionA cell has literally thousands of reactions occurring within its environment every minute. These reactions are not individual random events; rather they are chains of reactions, networked, that occur in response to a need. Therefore if product W is required, the chain of reactions A---E must occur as well as X---Z. I / / F--G--H / / A----B---->C---->D----> E + --------- W X---Y--ZThe sum of all chemical reactions within an organism defines metabolism. A given chain of chemical reactions is called a metabolic pathway.1Molecules are held together by covalent bonds. It took energy to create thesebonds and that energy is stored in the bonds. Energy stored is released when the bonds are broken. However it takes additional energy to break those bonds. Think of a match. It has stored chemical bond energy in the molecules on its tip. These do not spontaneously combust rather friction energy is used to initiate the chemical reaction. This start up energy is termed the energy of activation or Ea.Now think of the thousands of reactions occurring per minute in a cell. It takes time and considerable energy for these to occur. Too much time and too much energy are involved to effectively and efficiently support life. It takes time to build up to the energy levels need to reach Ea and the heat by-product can be harmful to the cell. Enzymes solved the heat and time problems.2Enzymes, usually proteins, are substances that act as biological catalysts (they speed up chemical reactions) for chemical reactions. Enzymes work by lowering the amount of energy it takes to start up or trigger a chemical reaction. Since less energy is required it not only reduces the heat by-productbut also speeds up the chemical reaction because it takes less time (1/10,000) to reach the lower Ea.Every biological chemical reaction within a cell requires an enzyme.Thus in the above example, the reaction A---B requires an enzyme; B----C also requires an enzyme but it is different from the enzyme catalyzing A---B.The cells different reactions require different enzymes. However if a bacteriahas an enzyme structurally the same as one found in humans, then that enzyme most likely performs the same task in both organisms. 3In chemical reactions such as ABA+B, AB is termed the reactant and A &B are called products.In enzyme equations, e.g. AB---e---A + B + e, AB is termed a “substrate” and A & B are “products”. Thus a substrate is a molecule that binds with anenzyme and undergoes chemical modification. A product is the result of the substrate change into a new type of molecule. Note that e, the enzyme, appears both before and after the reaction occurs. That’s because an enzyme is neither changed nor destroyed by the reaction. The enzyme is immediately reusable, some recycling more than a million times per minute, a very effective use of a resource.Enzyme equation: substrate + enzyme  product + enzymeIn most cases an enzyme is tied to a particular substrate. Thus the disaccharide sucrose has a particular enzyme, sucrase, to speed up its breakdown into its component parts of glucose and fructose.Sucrase gets its name from its substrate sucrose by using the suffix “ase”. The majority of enzymes are named by adding ase to the substrate’s name toreflect its working with that substrate only. Some enzymes, such as pepsin an enzyme found in your stomach, do not have the suffix since they work onmore than one substrate.Although enzymes are usually tied to a specific substrate, a given substrate may react with more than one enzyme producing the same product. Why? Topromote efficiency and lessen competition for given resources. Thus glucosemight be broken down in the liver by a different enzyme than the one that breaks it down in muscle cells. The peculiar 3-dimensional protein shape of an enzyme determines how it will catalyze and with what.4There is only one particular place on an enzyme that binds with a given substrate; that place is called the active site. It is here that the substrate undergoes a chemical modification permitting a speed up of the reaction. At the active site the enzyme and the substrate join in a weak noncovalent bond lasting only a few milliseconds. During this brief time the covalent bonds of the substrate either become stressed or are oriented in such a manner that they can be easily accessed/attacked by other molecules, completing the reaction. For example: in hydrolysis reactions water is used to break apart polymers into monomers. The monomers are bonded together covalently by the sharing of an oxygen molecule’s electrons. An enzyme-substrate bonding occurs stressing the oxygen molecule permitting the water to ‘break’ the covalent bonds thereby separating the monomers.5FACTORS AFFECTING REACTION RATEThe factors affecting enzyme reaction rates can be placed into two areas:1. The quantity of enzyme/substrate used in the reaction2. Physical factors (e.g. temperature) affecting the enzymePart 1: QuantityWhat happens to the reaction rate if one constantly adds either enzymes or substrates to the reaction? Does the rate increase, decrease, or stay the same, as the quantity is varied? We know that enzymes are neither permanently changed nor destroyed in an enzyme reaction. They work at a steady pace. They are reusable. We also know that substrate is changed into a new product, therefore if not replenished, can halt the reaction.?????? If substrate is abundant, what should happen to the reaction rate (amount of product formed/unit time) when more enzyme molecules are added to the reaction mixture? Graph your answer. (reaction rate: y-axis; enzyme: x-axis)6?????? If the amount of enzyme molecules remains constant, what would happen to the reaction rate when more substrate is added as product is formed? Graph your answer. (substrate: x-axis)Part 2: Physical FactorsPhysical factors affect enzyme reaction rates. We tend to work more effectively, more efficiently in given environments depending on the work required of us. Thus if the air conditioning breaks down and the ambient temperature is 105, it is hard to study but the high temperature does not effect our ability to learn how to swim. Enzymes work best in optimum pH, salt concentration and