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Biology Enzymes 20150828 www.njctl.org 2
Vocabulary Click on each word below to go to the definition. activation energy enzyme active site feedback inhibition allosteric regulation induced fit catalyst noncompetitive inhibitor coenzyme optimal pH cofactor optimal temperature competitive inhibitor substrate 3
Enzymes Unit Topics Click on the topic to go to that section · Enzymes, Catalytic Cycle · Temperature, pH, Inhibition · Allosteric Regulation, Feedback Inhibition 4
Enzymes, Catalytic Cycle Return to Table of Contents 5
Catalysts A catalyst is a substance which speeds up chemical reactions without being changed by the reaction. When a catalyst is present, less energy is needed to start a chemical reaction. When a catalyst is present, the speed of a chemical reaction is faster . The catalyst remains unchanged at the end of the reaction. 6
Enzymes Enzymes are catalysts in biological systems. In early cells, enzymes were made of ____________. In modern cells, enzymes are a type of ___________ . 7
Common Enzymes Lactase is an enzyme that helps us to digest dairy products. People with lactose intolerance have trouble digesting dairy because they lack this enzyme, but they are able to take a lactaid pill that contains the enzyme lactase. 8
Common Enzymes Amylase is an enzyme found in human saliva. It begins the chemical process of digestion. Typically, you can identify an enzyme by its ase ending. 9
Enzyme Substrate Complex Enzymes help chemical reactions occur by providing a space called an active site for the substrates (reactants), to bind. substrate Active site Substrate Products leaving Enzyme/substrate Enzyme/products entering active site of complex complex active site of enzyme enzyme Click here to see a video on Enzymes 10
Induced Fit Just as a key can only open a specific lock, each enzyme has its own unique shape, so each enzyme is specific to certain substrates. As the substrates enter the active site, the enzyme's shape changes just a little in order to create a better fit, called an induced fit . 11
Catalytic Cycle of an Enzyme An enzyme is capable of being used again and again to allow more of the same reactions to occur. 12
Which of the following acts as a catalyst in the 1 body? A Carbohydrates B Nucleic Acids Answer C Lipids D D Enzymes E Water 13
Another name for protein reactants is _____. 2 A products B substrates C active sites D enzymes Answer B 14
3 Enzymes bind only to certain substrates. True False Answer TRUE 15
4 An enzyme can only be used for one reaction and then it will not work again. True False Answer FALSE 16
Activation Energy Enzymes work by decreasing the minimum amount of energy required for reaction. This is called the activation energy , E a . Just as a ball cannot get over a hill if it does not roll up the hill with enough energy, a reaction cannot occur unless the molecules possess sufficient energy to get over the activation energy barrier. 17
Potential Energy Diagrams This activation energy is usually needed to break bonds in the substrate. final energy initial energy 18
Catalysts Enzymes increase the rate of a reaction by decreasing the activation energy of the reaction. This graph shows the decomposition of a sugar both with and without a catalyst. Notice that the initial energy of reactants and the final energy of the products are unchanged by the catalyst. 19
Activation energy is _____. 5 A the heat released in a reaction B the energy given off when reactants collide C generally very high for a reaction that takes place rapidly Answer D D an energy barrier between reactants and products 20
What happens to a catalyst in a reaction? 6 A It is unchanged. B It is incorporated into the products. C It is incorporated into the reactants. Answer A D It evaporates away. 21
Why does a catalyst cause a reaction to proceed 7 faster? A Only because there are more collisions per second. B Only because collision occur with greater energy. Answer C Only because the activation energy is lowered. C There are more frequent collisions and they D are of greater energy. 22
If a catalyst is used in a reaction _____. 8 A the energy of activation increases B different reaction products are obtained C the reaction rate increases Answer C D it evaporates away 23
Temperature, pH, Inhibition Return to Table of Contents 24
Enzymes Have Optimal Environments Since enzymes are proteins and proteins are sensitive to their environments, enzymes are also sensitive to their environments. Factors Affecting Enzyme Activity Temperature pH 25
Effect of Temperature on Enzymes In general, increasing the temperature of a system increases the reaction rate because the substrates are able to move faster and have more collisions with the active sites of the enzymes. This is true only up to certain temperatures for each type of enzyme! We call this temperature the optimal temperature. The optimal temperature is different for each type of enzyme. 26
Effect of Temperature on Enzymes Past the optimal temperature, the enzyme begins to denature or lose its shape, which changes the shape of the active site. 27
Optimal Temperature and Fever Fever is the elevation of body temperature above normal (In humans 98.6 o F). Typically, fevers develop in response to bacterial or viral infection. The optimal temperature for most bacterial enzymes is less than 98 o F, so by raising body temperature above that, the immune system attempts to denature the bacteria's enzymes and stop the infection. 28
Common Enzymes Laundry detergents contain enzymes that help break up and remove stains from your clothing. Why might you want to use a different laundry detergent when you wash clothes in hot water instead of in cold water? 29
Effect of pH on Enzymes pH level can also cause a denaturing of the enzyme. Increasingly Most biological solutions have pH Acidic values between 68. 30
Effect of pH on Enzymes (optimal pH = 4.2) The optimal pH for most enzymes is between 68, but again the optimal pH is different for each type of enzyme. 31
9 What is the optimal temperature for this enzyme? Answer about 40 o 32
10 What is the optimal pH of this enzyme? Answer 8 33
11 Which enzyme has a lower optimal temperature? Answer A 34
12 At which temperature do both enzymes have an equal rate of reaction? Answer about 45 o 35
13 Which description best explains the temperature effects shown in the graph? A Each enzyme will function at room temperature. B Both enzymes are inactive at the freezing point. C Each enzyme has its own optimal temperature range. Answer C D Both enzymes have the same optimal temperature range. 36
Based on this information which environment can you 14 conclude as being more acidic? A Stomach B Liver Answer A Stomach Enzyme Liver Enzyme 37
15 Which enzyme would you choose to use in a basic environment? A B C Answer C 38
16 The active site of an enzyme I. is the part where a substrate can fit II. can be used again and again III. is not affected by environmental factors A Answer I only D B II only C III only D I and II E I and III 39
Cofactors Sometimes enzymes need a helper to bind at the active site to make the enzyme active. These helpers are called cofactors . If the cofactors are organic molecules, then they are called coenzymes . Vitamins are a type of coenzyme. coenzyme substrate Enzyme 40
Enzyme Inhibitors Certain chemicals work to stop or inhibit the enzymes. These chemicals are called enzyme inhibitors. Types of Inhibitors · Competitive Inhibitors · Noncompetitive Inhibitors click here for an animation about inhibition 41
Competitive Inhibitors Competitive inhibitors are similar in shape to the Competitive inhibitor substrates. They are able to block the substrates from binding to the active site by binding to the active site themselves. 42
Competitive Inhibitors: How They Are Stopped To stop competitive inhibition, the concentration of the substrates needs to be increased so that they outnumber the inhibitors. This way, the substrates are more likely to bind to the active site before an inhibitor does. 43
Noncompetitive Inhibitors: How they work Noncompetitive inhibitors bind to a separate part of the enzyme and cause the enzyme to change shape. When the enzyme changes shape, the substrate is no longer able to bind to the active site because the active site also changes shape. This type of inhibition is sometimes irreversible. 44
Organic molecules that aid in the action of the enzyme 17 are called ____. A products B coenzymes C Answer substrates B D helpers 45
18 Which type of inhibitor binds at the active site? A Competitive Inhibitor B Noncompetitive Inhibitor Answer A 46
19 Noncompetitive inhibitors are similar in shape to the substrates that bind at the active site of an enzyme. True Answer False FALSE 47
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