1. ENZYMES AND HOMEOSTASIS Enzymes

2. LEARNING GOALS I CAN … …explain how enzymes speed up the rate of a chemical reaction …discuss the properties of enzymes that make them specific to only one kind of reaction. …explain how enzymes can be used repeatedly until they are destroyed by other enzymes …describe how cofactors and inhibitors regulate enzyme activity …explain how changes in temperature, pH, and enzyme concentration affect the efficiency of enzyme action

3. Organic macromolecules: proteins III. Enzymes A. Enzymes A. Enzymes are protein catalysts that help speed up chemical reactions in living things only. a type of protein in all living things that speed up the rate of chemical reactions Enzyme – a type of protein in all living things that speed up the rate of chemical reactions substrates 1. Enzymes work by manipulating substrates a reactant that an enzyme acts on to speed up a chemical reaction Substrate – a reactant that an enzyme acts on to speed up a chemical reaction

4. Organic macromolecules: proteins 2. An enzyme can speed up chemical reactions by: Twisting and breaking bonds to make the number of products greater than the number of substrates.(catabolic) Twisting and breaking bonds to make the number of products greater than the number of substrates.(catabolic) Holding substrates together making the number of products less than the number of substrates.(anabolic) Holding substrates together making the number of products less than the number of substrates.(anabolic)

5. Organic macromolecules: Proteins unique and only specific substrates will fit into its active site. B. The shape of the enzyme is unique and only specific substrates will fit into its active site. the part of an enzyme where manipulation of the substrate occurs Active site – the part of an enzyme where manipulation of the substrate occurs the enzyme is free to act on another substrate until it is metabolized (chemically destroyed). 1. Once an enzyme acts on a substrate the enzyme is free to act on another substrate until it is metabolized (chemically destroyed). then the enzyme will have the wrong shape which means the substrate won’t fit into the active site. 2. If during protein synthesis amino acids are not placed in the proper order then the enzyme will have the wrong shape which means the substrate won’t fit into the active site. *Cause of many recessive traits and genetic disorders.

6. Organic macromolecules: proteins

7. Enzymes and Homeostasis I. How Enzymes work substrate A. The reactant that an enzyme acts on is the substrate. enzyme-substrate complex 1. The enzyme binds to a substrate, or substrates, forming an enzyme-substrate complex. the catalytic action of the enzyme converts the substrate to the product or products. 2. While the enzyme and substrate are bound, the catalytic action of the enzyme converts the substrate to the product or products. specific B. The reaction catalyzed by each enzymes is very specific. 1. What accounts for this molecular recognition? The specificity of an enzyme results from its three- dimensional shape.

8. Enzymes and Homeostasis to the fit between the active site and the substrate 2. The specificity of an enzyme is due to the fit between the active site and the substrate. induced fit a. As the substrate enters the active site, interactions between the substrate and the amino acids of the protein causes the enzyme to change shape slightly, leading to a tighter induced fit that brings chemical groups in position to catalyze the reaction. portion 3. Only a portion of the enzyme binds to the substrate. The active site of an enzyme is typically a pocket or groove on the surface of the protein into which the substrate fits a. The active site of an enzyme is typically a pocket or groove on the surface of the protein into which the substrate fits. The active site is usually formed by only a few amino acids. b. The active site is usually formed by only a few amino acids.

9. LE 8-16 Substrate Active site Enzyme Enzyme-substrate complex

10. Enzymes and Homeostasis hydrogen bonds ionic bonds 4. In most cases, substrates are held in the active site by weak interactions, such as hydrogen bonds and ionic bonds. a. R groups a. R groups of a few amino acids on the active site catalyze the conversion of substrate to product. product b. The product then leaves the active site. thousands of reactions a second. 5. A single enzyme molecule can catalyze thousands of reactions a second. unaffected by the reaction and are reusable. 6. Enzymes are unaffected by the reaction and are reusable.

11. LE 8-17 Enzyme-substrate complex Substrates Enzyme Products Substrates enter active site; enzyme changes shape so its active site embraces the substrates (induced fit). Substrates held in active site by weak interactions, such as hydrogen bonds and ionic bonds. Active site (and R groups of its amino acids) can lower E A and speed up a reaction by acting as a template for substrate orientation, stressing the substrates and stabilizing the transition state, providing a favorable microenvironment, participating directly in the catalytic reaction. Substrates are converted into products. Products are released. Active site is available for two new substrate molecules.

12. Enzymes and Homeostasis forwardreverse C. Most metabolic enzymes can catalyze a reaction in both the forward and reverse directions. on the relative concentrations of products and reactants 1. The actual direction depends on the relative concentrations of products and reactants the maintenance of homeostatic balances within the body a. These concentrations are dependent on the maintenance of homeostatic balances within the body b. Negative b. Negative feedback loops are the most common mechanisms to maintain necessary enzyme concentrations. (usually controlled by Negative Feedback Mechanisms). 2. Enzymes catalyze reactions in the direction of equilibrium (usually controlled by Negative Feedback Mechanisms).

13. Enzymes and Homeostasis lower D. Enzymes use a variety of mechanisms to lower activation energy and speed up a reaction. the active site brings substrates together in the correct orientation for the reaction to proceed. 1. In reactions involving more than one reactant, the active site brings substrates together in the correct orientation for the reaction to proceed. it may put stress on bonds that must be broken, making it easier for the reactants to reach the transition state, or break bonds to form products. 2. As the active site binds the substrate, it may put stress on bonds that must be broken, making it easier for the reactants to reach the transition state, or break bonds to form products.

14. An Introduction to Metabolism II. Enzyme Activity temperaturepH cofactorsenzyme concentration A. The activity of an enzyme is affected by general environmental conditions such as temperature, pH, cofactors, and enzyme concentration. optimal 1. Each enzyme works best at certain optimal conditions, which favor the most active conformation for the enzyme molecule. unfavorable 2. When conditions are unfavorable it may have a direct effect on the body’s ability to maintain homeostasis.

15. An Introduction to Metabolism Temperature B. Temperature has a major impact on reaction rate. collisions between substrates and active sites occur more frequently as molecules move more rapidly. 1. As temperature increases, collisions between substrates and active sites occur more frequently as molecules move more rapidly. thermal agitation begins to disrupt the weak bonds that stabilize the protein’s active conformation, and the protein denatures. 2. As temperature increases further, thermal agitation begins to disrupt the weak bonds that stabilize the protein’s active conformation, and the protein denatures. 3. Each enzyme has an optimal temperature. 35-40 o C (95-104 o F) a. Most human enzymes have optimal temperatures of about 35-40 o C (95-104 o F) 70 o C (159 o F) b. Bacteria that live in hot springs contain enzymes with optimal temperatures of 70 o C (159 o F)

16. Enzymes and Homeostasis C. Each enzyme also has an optimal pH. 1. Maintenance of the active conformation of the enzyme requires a particular pH: This falls between pH 6 and 8 for most enzymes. This falls between pH 6 and 8 for most enzymes. However, digestive enzymes in the stomach are designed to work best at pH 2, while those in the intestine have an optimum of pH 8. However, digestive enzymes in the stomach are designed to work best at pH 2, while those in the intestine have an optimum of pH 8. cofactors D. Many enzymes require nonprotein helpers, called cofactors, for catalytic activity. permanentlyreversible 1. Cofactors bind permanently or reversible to the enzyme. zincironcopper 2. Some inorganic cofactors include zinc, iron, and copper. coenzymesvitamins 3. Organic cofactors are called coenzymes. Many vitamins are coenzymes.

17. LE 8-18 Optimal temperature for typical human enzyme Optimal temperature for enzyme of thermophilic (heat-tolerant bacteria) Temperature (°C) Optimal temperature for two enzymes 020 40 6080100 Rate of reaction Optimal pH for pepsin (stomach enzyme) Optimal pH for trypsin (intestinal enzyme) pH Optimal pH for two enzymes 0 Rate of reaction 1 23 45 67 8 910

18. Enzymes and Homeostasis rate E. The rate that a specific number of enzymes convert substrates to products depends in part on substrate concentrations. low 1. At low substrate concentrations, an increase in substrate concentration speeds binding to available active sites. there is a limit to how fast a reaction can occur. 2. However, there is a limit to how fast a reaction can occur. high saturated a. At high substrate concentrations, the active sites on all enzymes are engaged. The enzyme is saturated. the speed at which the active site can convert substrate to product. b. Now, the rate of the reaction is determined by the speed at which the active site can convert substrate to product. to add more enzyme molecules. 3. The only way to increase productivity when the enzyme is saturated is to add more enzyme molecules.

19. Enzymes and Homeostasis I. The Body’s Control of Enzyme Activity feedback inhibition The product acts as an inhibitor of an enzyme in the pathway (Negative Feedback). A. A common method of metabolic control is feedback inhibition in which an early step in a metabolic pathway is switched off by the pathway’s final product. The product acts as an inhibitor of an enzyme in the pathway (Negative Feedback). prevents a cell from wasting chemical resources by synthesizing more product than is needed. B. Feedback inhibition prevents a cell from wasting chemical resources by synthesizing more product than is needed.