【生化（英文）教案】Chapter 5Enzymes

1、Charpter 5 Enzymes1. Objective and requirement (1) After learning this chapter, students should have a good mastery of properties of enzymes; factors affecting reaction velocity(substrate concentration, teperature and pH); competitive & noncompetitive inhibition of enzymes; regulation of enzymes

2、.(2) After learning this chapter, students should have a fair knowledge of how enzymes work; enzyme application in clinical diagnosis; (3)After learning this chapter, students should have some acquaintance with nomenclature of enzymes; Michaelis-Menten equation and Lineweaver- Burk plot; enzyme inhi

3、bitors as drugs; induction and repression of enzyme synthesis. 2. Major teaching contents. OVERVIEW. NOMENCLATURE. PROPERTIES OF ENZYMES. HOW ENZYMES WORK. FACTORS AFFECTING REACTION VELOCITY. MICHAELIS-MENTEN EQUATION. INHIBITION OF ENZYME ACTIVITY. REGULATION OF ENZYME ACTIVITY. ENZYMES IN CLINICA

4、L DIAGNOSIS. CHAPTER SUMMARY3. Important points(1) properties of enzymes; (2) factors affecting reaction velocity(substrate concentration, teperature and pH); (3)competitive & noncompetitive inhibition of enzymes; (4)regulation of enzymes4. Difficult points(1) how enzymes work (2) Michaelis-Ment

5、en equation & Lineweaver-Burk plot;5. Teaching method: Heuristic6. Teaching aid: Multimedia Courseware7.Teacher : Zeng Wei Min8.Students: the Grade 2010 students majoring in biological science9. Classroom: T111 classroom10. Textbook Lippincott's Illustrated Reviews: Biochemistry (5th edition

6、) by Pamela C. Champe, 2011年出版11. Reference 1. 生物化学 王镜岩主编 第三版，北京：人民卫生出版社，20022. 生物化学 周爱儒等主编 第七版 北京 人民卫生出版社，20083. Instant Notes in Biochemistry B.D.Hames,N.M.Hooper and J.D.Houghton. Bios Scientific Publishers Limited,1997 4. Medical Biochemistry (Second Edition),Alexander C. Brownie & John C. K

7、ernohan, 2005Chapter 5 Enzymes. OVERVIEW1. All reactions in the body are mediated by the biological catalysts. 2. All enzymes are proteins except some RNAs(ribozyme) & not all proteins are enzymes.3. Here enzymes are protein catalysts that are synthesized by active cells and increase the rate of

8、 reactions without being changed in the overall process. NOMENCLATUREThere are two nomenclature methods for enzymes. -A. Recommended name Short & convenient for everyday use. Suffixing “-ase” after the substrate of the reaction (elastase, proteinase, urease, glucosidase ) Describing the enzymati

9、c action (lactate dehydrogenase, hydroxylase, adenylyl cyclase). Others (trpsin, pepsin)-B. Systemic name Developed by the International Union of Biochemstry & Molecular Biology(IUBMB). The more complete, unambiguous name. The suffix “-ase” is attached to a complete description of the reaction c

10、atalyzed, including the names of all the substrates. Enzymes are divided into six major classes, each with numerous subgroups.The 4th enzyme to be assigned to this classSystemic nameThe enzyme Communissione.g.trypsin: EC 3. 4. 21. 4hydrolaseProtease (hydrolazes peptide bond)Ser protease (with a Ser

11、at the active site). PROPERTIES OF ENZYMES As biological catalyst, enzyme has numerous properties, such as Enzyme catalyzed reactions are much faster than uncatalyzed reactions. Enzyme catalyzed reactions display saturation kinetics with respect to substrate concentration Relatively mild conditions(

12、T, pH) Enzyme catalyzed reactions can be regulated Enzyme are highly specific.-A. Active sites-B. Catalytic efficiency Most enzyme-catalyzed reactions are 103 to 108 times faster than uncatalyzed reactions. Each enzyme molecule may catalyze 100 to 1000 subs-trate molecules transforming into product

13、each second. The number of substrate molecules converted to product per enzyme molecule per second is called the turnover number, or kcat. (equal to Vm/E)-C. Specificity Enzymes are highly specific, interacting with one or a few substrates & catalyzing only one type of chemical reaction. Absolut

14、e specificity: (e.g.,urease) Relative specificity: (e.g.,esterase) Stereo specificity: (e.g., D-amino acid oxidase)-D. HoloenzymesOn the basis of composition of enzyme moleculesingle enzyme ： contain AAs only conjugated enzymeapoenzymeenzymecofactormetal ionsmall organic molecules(variation of vitam

15、in precursors)Coenzyme(cosubstrate)prosthetic groupholoenzymecofactor-E. Regulation(detail in )-F. Location within the cell Compartmentalization of enzymes. HOW ENZYMES WORK First, an enzyme must bind to a substrate at the active site. Then, energy changes during the reaction. And the active site ch

16、emically facilitates catalysis. -A. Energy changes occurring during the reaction-B. Chemistry of the active site-B-1. Transition-state stabilization-B-2. Other mechanisms-B-3. Visualization of the transition state. FACTORS AFFECTING REACTION VELOCITY The rate or velocity of a reaction(V) is the numb

17、er of substrate molecules converted to product per unit time; It is usually expressed as mol of product formed per minute. Key factors: S, temperature, & pH Enzymic responses to these factors in vitro only give us some clues to study in vivo. -A. Substrate concentration-B. Temperature(T)-C. pH.

18、MICHAELIS-MENTEN EQUATIONThe Relationship between Substrate concentration & Reaction Rate can be Expressed Quantitatively(proposed by Michaelis and Menten in 1913yr.Leonor Michaelis (1875-1949) Maud Menten (1879-1960)-A. Reaction model-B. Michaelis-Menten equation-B-1. Relative concentrations of

19、 E & S-B-2. Steady-state assumption-B-3. Initial velocity-C. Important conclusions about Michaelis-Menten kinetcs-C-1. Characteristics of Km-C-2. Relationship of velocity to E-C-3. Order of reaction -D. Lineweaver-Burk plot. INHIBITION OF ENZYME ACTIVITY Any substance that can diminish the rate

20、of an enzyme-catalyzed reaction is known as the inhibitor of enzyme. Irreversible inhibitors bind to enzymes through covalent bonds. Reversible inhibitors bind to enzymes through noncovalent bonds, the binding is reversible. There are two primary types of reversible inhibitor, the competitive &

21、noncompetitive inhibitor -A. Competitive inhibition -A-1. Effect on Vmax-A-2. Effect on Km-A-3. Effect on the Lineweaver-Burk plot -A-4. Statin drug as examples of competitive inhibitors-B. Noncompetitive inhibition -B-1. Effect on Vmax-B-2. Effect on Km-B-3. Effect on Lineweaver-Burk plot-B-4. Exam

22、ples of noncompetitive inhibitors-C. Enzyme inhibitors as drugsAbout 20% of drugs are the enzyme inhibitors. REGULATION OF ENZYME ACTIVITY How do cells control specific biochemical reactions? (enzyme activity; E; enzyme location; S; & products conversion ) In metabolic pathway, there is at least

23、 one enzyme that set the rate of overall sequence Regulatory Enzyme There are two major classes of regulatory enzymes in metabolic pathway.-A. Allosteric binding sites-A-1. Homotropic effectors-B. Regulation of enzymes by covalent modification-B-1. Phosphorylation & dephosphorylation-B-2. Response of enz