CHAPTER 8 Enzymes as Catalysts OBJECTIVES: 1. Define catalytic power. 2. What is meant by substrate specificity of an enzyme? 3. What is the active site? 4. Explain the Induced Fit Theory Model for Substrate Binding. What was the major shortcoming of the Lock-and-Key Model for Substrate Binding? 5. Explain catalytic power in terms of the transition state and activation energy. 6. Be able to define the following terms: cofactor, coenzyme, and prosthetic group 7. What does an activation-transfer coenzyme do? 8. With respect to thiamine pyrophosphate, what vitamin is it synthesized from? What group on substrate (pyruvate or a-ketoglutarate for example) is always attacked by this coenzyme? Which bond is broken? 9. With respect to Coenzyme A, what vitamin is it synthesized from? What is its functional group on the coenzyme and what kind of bond does it form with the activated group? What types of groups are activated? 10. Concerning biotin, what kind of enzyme uses this coenzyme and what do they do? What is the vitamin? Is biotin a prosthetic group? 11. Concerning the cofactor pyridoxal phosphate, what type of group does it usually react with? What vitamins is it synthesized from (see your lecture notes or use the textbook index)? 12. Concerning NAD+, what vitamin is it synthesized from? When lactate dehydrogenase or alcohol dehydrogenase oxidize their substrates, what is transferred to NAD+? Besides pyruvate and acetaldehyde, what is the other reaction product? What is the function of the ADP portion of NAD+? 13. Be able to draw a probable plot of activity versus pH for an enzyme that functions at pH=7.0. 14, Be able to draw a probable plot of activity versus temperature for a human enzyme. 15. What is the normal function of acetylcholinesterase? Explain how diisopropylphosphofluoridate causes the symptoms associated with it. Is this an irreversible inhibitor? Why? 16. How does aspirin inhibit prostaglandin endoperoxide synthase? 17. Concerning penicillin, why does it bind so readily to the active site of the enzyme? Is penicillin an irreversible inhibitor? Is penicillin a suicide inhibitor? Why? 18. What is the normal function of xanthine oxidase. Explain why allopurinol is used to treat gout. Is allopurinol an irreversible inhibitor? Is allopurinol a suicide inhibitor? Why? 19. Concerning penicillin, why does it bind so readily to the active site of the enzyme? Is penicillin an irreversible inhibitor? Is penicillin a suicide inhibitor? Why? 20. In general terms, why are heavy metals toxic? 21. Be able to name the 6 major classes of enzymes. Given one of the following reactions, be able to match it with one of the 6 major classes of enzyme reactions catalyzed: alcohol dehydrogenase, glucokinase, chymotrypsin, aldolases, triosephosphate isomerase, and pyruvate carboxylase. 22. What is the difference between a synthase and a synthetase? 23. Concerning Dennis "the menace" Veere, Explain how Malathion causes the symptoms associated with it. Is the inhibition irreversible? Why? Is this an example of a suicide inhibitor? Why? 24. Concerning Lotta Topaigne, Explain why allopurinol is used to treat gout. What is the normal reaction inhibited by this drug? Is allopurinol an irreversible inhibitor? Is allopurinol a suicide inhibitor? Why? 25. Concerning Al Martini, be able to write the equation for the first step in alcohol metabolism in humans. What vitamin is the coenzyme of this reaction synthesized from? What is the common vitamin deficiency seen in alcoholics? Why does it occur? 23. Understand the meaning of each of the keywords. KEYWORDS: acetate, acetylates, acetylcholine, acetylcholinesterase, acetylsalicylic acid, activation energy, active site, acyl groups, alcohol dehydrogenase, allopurinol, amino group, aspirin, biotin, carbonyl carbon, carboxylase, catalytic power, coenzyme A, coenzymes, cofactors, covalent bond, choline dehydrogenases, cyclooxygenase, diisopropylphosphofluoridate, enzyme specificity, hydrolase, hydride ion, hypoxanthine, induced fit, isomerase, lead, ligase, lyase, mercury, model, inhibitor, oxidoreductases, oxime, cyclooxygenase, prosthetic groups, pyridoxal, pyridoxal phosphate, pyridoxamine, pyridoxine, pyruvate carboxylase, serine, suicide inhibitor, synthetase, thiamine [B1], thiamine pyrophosphate, thioester, bonds, transition state analogue, transferase, state complex, urate, uric acid crystals, vitamin B6, xanthine, xanthine dehydrogenase, xanthine oxidase, ASSIGNMENTS: Examine questions in chapter 8 Work questions 1-5 at the end of Chapter 8 Understand the meaning of the key words in the context of Chapter 8 Practice Questions for Chapter 8 Objectives No Other Help REFERENCE: Marks' Basic Medical Biochemistry: A Clinical Approach, 2nd Edition, 2004, Williams and Wilkins (ISBN: 0-7817-2145-8) by Colleen M. Smith PhD, Allan D. Marks MD, and Michael A. Lieberman PhD