1. 1 Energy and Metabolism

2. 2 The Energy of Life The living cell generates thousands of different reactions Metabolism Is the totality of an organism’s chemical reactions Arises from interactions between molecules An organism’s metabolism transforms matter and energy, subject to the laws of thermodynamics

3. 3 Enzymes Lower the E A Barrier Progress of the reaction Products Course of reaction without enzyme Reactants Course of reaction with enzyme EAEA without enzyme E A with enzyme is lower ∆G is unaffected by enzyme Free energy

4. 4 Enzymes Are Biological Catalysts that… Are proteins that carry out most catalysis in living organisms. Are highly specific that can speed up only one or a few chemical reactions. Have unique three-dimensional shape that enables an enzyme to stabilize a temporary association between substrates. It is not changed or consumed in the reaction, only a small amount is needed, and can then be reused. By controlling which enzymes are made, a cell can control which reactions take place in the cell.

5. 5 Substrate Specificity of Enzymes Almost all enzymes are globular proteins with one or more active sites on their surface. The substrate is the reactant an enzyme acts on enzyme-substrate complex Reactants bind to the active site to form an enzyme-substrate complex. The 3-D shape of the active site and the substrates must match, like a lock and key Substate Active site Enzyme

6. 6 Substrate Specificity of Enzymes Binding of the substrates causes the enzyme to adjust its shape slightly, leading to a better induced fit. Induced fit of a substrate brings chemical groups of the active site into positions that enhance their ability to catalyze the chemical reaction When this happens, the substrates are brought close together and existing bonds are stressed. This reduces the amount of energy needed to reach the transition state. Enzyme- substrate complex

7. 7 The Catalytic Cycle Of An Enzyme Substrates Products Enzyme Enzyme-substrate complex 1 Substrates enter active site; enzyme changes shape so its active site embraces the substrates (induced fit). 2 Substrates held in active site by weak interactions, such as hydrogen bonds and ionic bonds. 3 Active site can lower E A and speed up a reaction by acting as a template for substrate orientation, stressing the substrate bonds and stabilizing the transition state, providing a favorable microenvironment, participating directly in the catalytic reaction. 4 Substrates are converted into Products. 5 Products are Released. 6 Active site Is available for two new substrate Mole. Figure 8.17

8. 8 1 The substrate, sucrose, consists of glucose and fructose bonded together. Bond Enzyme Active site The substrate binds to the enzyme, forming an enzyme-substrate complex. 2 H2OH2O The binding of the substrate and enzyme places stress on the glucose-fructose bond, and the bond breaks. 3 Glucose Fructose Products are released, and the enzyme is free to bind other substrates. 4 The Catalytic Cycle Of An Enzyme

9. 9 Factors Affecting Enzyme Activity Temperature - rate of an enzyme-catalyzed reaction increases with temperature, but only up to an optimum temperature. pH - ionic interactions also hold enzymes together. Inhibitors and Activators

10. 10 Effects of Temperature and pH Each enzyme has an optimal temperature in which it can function Optimal temperature for enzyme of thermophilic Rate of reaction 0 20 40 80 100 Temperature (Cº) (a) Optimal temperature for two enzymes Optimal temperature for typical human enzyme (heat-tolerant) bacteria

11. 11 Effects of Temperature and pH Each enzyme has an optimal pH in which it can function Figure 8.18 Rate of reaction (b) Optimal pH for two enzymes Optimal pH for pepsin (stomach enzyme) Optimal pH for trypsin (intestinal enzyme) 1 02 34 5 6789

12. 12 Factors Affecting Enzyme Activity Inhibitor - substance that binds to an enzyme and decreases its activity – feedback Competitive inhibitors - compete with the substrate for the same active site Noncompetitive inhibitors - bind to the enzyme in a location other than the active site Allosteric sites - specific binding sites acting as on/off switches

13. 13 Enzyme Inhibitors Competitive inhibitors b ind to the active site of an enzyme, competing with the substrate (b) Competitive inhibition A competitive inhibitor mimics the substrate, competing for the active site. Competitive inhibitor A substrate can bind normally to the active site of an enzyme. Substrate Active site Enzyme (a) Normal binding

14. 14 Enzyme Inhibitors Noncompetitive inhibitors bind to another part of an enzyme, changing the function A noncompetitive inhibitor binds to the enzyme away from the active site, altering the conformation of the enzyme so that its active site no longer functions. Noncompetitive inhibitor (c) Noncompetitive inhibition

15. 15 Regulation Of Enzyme Activity Helps Control Metabolism Chemical chaos would result if a cell’s metabolic pathways were not tightly regulated To regulate metabolic pathways, the cell switches on or off the genes that encode specific enzymes

16. 16 Regulation Of Enzyme Activity Helps Control Metabolism Allosteric regulation is the term used to describe any case in which a protein’s function at one site is affected by binding of a regulatory molecule at another site Enzymes change shape when regulatory molecules bind to specific sites, affecting function

17. 17 allostery The term allostery comes from the Greek allos, "other", and stereos, "solid (object)", in reference to the fact that the regulatory site of an allosteric protein is physically distinct from its active site.

18. 18 Allosteric Activation and Inhibition Most allosterically regulated enzymes are made from polypeptide subunits Each enzyme has an active and an inactive form

19. Allosteric Activation The binding of an activator stabilizes the active form of the enzyme.

20. 20 Allosteric Inhibition The binding of an inhibitor stabilizes the inactive form of the enzyme

21. 21 Stabilized inactive form Allosteric activater stabilizes active from Allosteric enyzme with four subunits Active site (one of four) Regulatory site (one of four) Active form Activator Stabilized active form Allosteric activater stabilizes inactive form Inhibitor Inactive form Non- functional active site (a) Allosteric activators and inhibitors. In the cell, activators and inhibitors dissociate when at low concentrations. The enzyme can then oscillate again. Oscillation

22. 22 Cooperativity Is a form of allosteric regulation that can amplify enzyme activity Binding of one substrate molecule to active site of one subunit locks all subunits in active conformation. Substrate Inactive form Stabilized active form (b) Cooperativity: another type of allosteric activation. Note that the inactive form shown on the left oscillates back and forth with the active form when the active form is not stabilized by substrate.

23. 23 Factors Affecting Enzyme Activity Activators - substances that bind to allosteric sites and keep the enzymes in their active configurations - increases enzyme activity Cofactors - chemical components that facilitate enzyme activity Coenzymes - organic molecules that function as cofactors

24. 24 Regulation of Biochemical Pathways Biochemical pathways must be coordinated and regulated to operate efficiently. Advantageous for cell to temporarily shut down biochemical pathways when their products are not needed

25. 25

26. 26 Positive Feedback in Coagulation

27. 27 In Feedback Inhibition: The end product of a metabolic pathway shuts down the pathway When the cell produces increasing quantities of a particular product, it automatically inhibits its ability to produce more of the substance Active site available Isoleucine used up by cell Feedback inhibition Isoleucine binds to allosteric site Active site of enzyme 1 no longer binds threonine; pathway is switched off Initial substrate (threonine) Threonine in active site Enzyme 1 (threonine deaminase) Intermediate A Intermediate B Intermediate C Intermediate D Enzyme 2 Enzyme 3 Enzyme 4 Enzyme 5 End product (isoleucine)

28. 28 Harmful Effects of Positive Feedback Positive feedback can be harmful. Two specific examples of these harmful outcomes would be: 1.Fever can cause a positive feedback within homeostasis that pushes the body temperature continually higher. If the temperature reaches 45 degrees centigrade (113 degrees Fahrenheit) cellular proteins denature bringing metabolism to a stop and death. 2.Chronic hypertension can favor the process of atherosclerosis which causes the openings of blood vessels to narrow. This, in turn, will intensify the hypertension and bring on more damage to the walls of blood vessels.

29. 29 http://www.mhhe.com/biosci/esp/2002_gener al/Esp/folder_structure/tr/m1/s7/trm1s7_3.ht m http://www.mhhe.com/biosci/esp/2002_gener al/Esp/folder_structure/tr/m1/s7/trm1s7_3.ht m http://www.hopkinsmedicine.org/hematology/ Coagulation.swf http://www.hopkinsmedicine.org/hematology/ Coagulation.swf http://www.youtube.com/watch?v=hb92wr93 JrE http://www.youtube.com/watch?v=hb92wr93 JrE