1. Online Counseling Resource YCMOU ELearning Drive… School of Architecture, Science and Technology Yashwantrao Chavan Maharashtra Open University, Nashik – 422222, India

2. SEP-SBI091-CP1-03 Introduction Programmes and Courses SEP –SBI091- U01 -CP1_03

3. School of Science and Technology, Online Counseling Resource… Credits  Academic Inputs by Sonali Alkari Faculty YCMOU Nagpur Centre, Faculty LAD college P.G. D of Biotechnology Research officer Ankur Seeds Pvt Ltd sonalisa_alkari@yahoo.co.in Sonalisaal@rediffmail.com 3© 2008, YCMOU. All Rights Reserved.

4. School of Science and Technology, Online Counseling Resource… © 2008, YCMOU. All Rights Reserved.4 How to Use This Resource  Counselor at each study center should use this presentation to deliver lecture of 40-60 minutes during Face-To-Face counseling.  Discussion about students difficulties or tutorial with assignments should follow the lecture for about 40-60 minutes.  Handouts (with 6 slides on each A4 size page) of this presentation should be provided to each student.  Each student should discuss on the discussion forum all the terms which could not be understood. This will improve his writing skills and enhance knowledge level about topics, which shall be immensely useful for end exam.  Appear several times, for all the Self-Tests, available for this course.  Student can use handouts for last minutes preparation just before end exam.

5. School of Science and Technology, Online Counseling Resource… © 2008, YCMOU. All Rights Reserved.5 Learning Objectives  After studying this module, you should be able to : Describe Action of enzymes Describe Lock-and-Key model, Describe Induced-fit model; Discuss Active site concept,

6. School of Science and Technology, Online Counseling Resource… Characteristics of Enzymes-1  Enzymes exhibit four fundamental characteristics.  First, enzymes do not make a reaction occur that would not occur on its own, they just make it happen much faster.  Second, the enzyme molecule is not permanently altered by the reaction.  It may be changed transiently, but the enzyme at the end of the reaction is the same molecule it was at the beginning.  Therefore, a single enzyme molecule can be used over and over to catalyze the same reaction. © 2008, YCMOU. All Rights Reserved.6

7. School of Science and Technology, Online Counseling Resource… Characteristics of Enzymes-2  Third, an enzyme can catalyze both the forward and the reverse reaction. One direction may be more favorable than the other, but the unfavorable direction of the reaction can occur.  Fourth, enzymes are highly specific for the substrates they bind, meaning they catalyze only one reaction.  Because of thee conformation of the complex protein molecule, the uniqueness of its active site and the structural configuration of the substrate molecule, an enzyme will select only specific compound for attack. © 2008, YCMOU. All Rights Reserved.7

8. School of Science and Technology, Online Counseling Resource… Enzyme Specificity  An enzyme will usually exhibit group specificity ; a general group of compounds may serve as substrate.  If the enzyme attack only one single substrate,for example glucose and no other monosaccharide it is, said to have an absolute group specificity.  Enzyme may have relative group specificity it attacks a homologous series of aldohexoses.  Enzymes possess stereo-specificity towards substrate.  Thus enzymes may have optical specificity towards substrate. © 2008, YCMOU. All Rights Reserved.8

9. School of Science and Technology, Online Counseling Resource… How Enzymes Work-1  They create an environment to make the reaction energetically more favorable.  This environment, the active site, is typically a pocket or groove that is lined with amino acids whose side chains bind the substrate (such as sugar) and aid in its chemical transformation to products.  Therefore, the amino acids that form the active site provide the specificity of substrate binding and the proper chemical environment so that the reaction occurs more rapidly than it otherwise would. © 2008, YCMOU. All Rights Reserved.9

10. School of Science and Technology, Online Counseling Resource… How Enzymes Work-2  The distinguishing feature of an enzyme- catalyzed reaction is that it takes place within the confines of a pocket on the enzyme called the active site.  The molecule that is bound in the active site and acted upon by the enzyme is called the substrate.  The surface of the active site is lined with amino acid residues with substituent groups that bind the substrate and catalyze its chemical transformation.  Often, the active site encloses a substrate, sequestering it completely from solution. © 2008, YCMOU. All Rights Reserved.10

11. School of Science and Technology, Online Counseling Resource… How Enzymes Work-3  The enzyme substrate complex, whose existence was first proposed by Charles- Adolphe Wurtz in 1880, is central to the action of enzymes.  It is also the starting point for mathematical treatments that define the kinetic behavior of enzyme-catalyzed reactions and for theoretical descriptions of enzyme mechanisms. © 2008, YCMOU. All Rights Reserved.11

12. School of Science and Technology, Online Counseling Resource… How Enzymes Work-4  A simple enzymatic reaction might be written E + S = ES = EP = E+ P  where E, S, and P represent the enzyme, substrate, and product; ES and EP are transient complexes of the enzyme with the substrate and with the product.  The function of a catalyst is to increase the rate of a reaction. Catalysts do not affect reaction equilibria.  Any reaction, such as S P, can be described by a reaction coordinate diagram, a picture of the energy changes during the reaction. energy in biological systems is described in terms of free energy, G. © 2008, YCMOU. All Rights Reserved.12

13. School of Science and Technology, Online Counseling Resource… How Enzymes Work-5 © 2008, YCMOU. All Rights Reserved.13

14. School of Science and Technology, Online Counseling Resource… How Enzymes Work-6  In the coordinate diagram, the free energy of the system is plotted against the progress of the reaction (the reaction coordinate).  The starting point for either the forward or the reverse reaction is called the ground state, the contribution to the free energy of the system by an average molecule (S or P) under a given set of conditions.  To describe the free-energy changes for reactions, chemists define a standard set of conditions (temperature 298 K; partial pressure of each gas 1 atm, or 101.3 kPa; concentration of each solute 1 M) © 2008, YCMOU. All Rights Reserved.14

15. School of Science and Technology, Online Counseling Resource… Reaction Coordinate Diagram © 2008, YCMOU. All Rights Reserved.15

16. School of Science and Technology, Online Counseling Resource… How Enzymes Work-7  And express the free-energy change for this reacting system as G, the standard free energy change.  A favorable equilibrium does not mean that the SnP conversion will occur at a detectable rate. The rate of a reaction is dependent on an entirely different parameter.  There is an energy barrier between S and P: the energy required for alignment of reacting groups, formation of transient unstable charges, bond rearrangements, and other transformations required for the reaction to proceed in either direction. © 2008, YCMOU. All Rights Reserved.16

17. School of Science and Technology, Online Counseling Resource… How Enzymes Work-8  This is illustrated by the energy “hill” in Figures.  To undergo reaction, the molecules must overcome this barrier and therefore must be raised to a higher energy level.  At the top of the energy hill is a point at which decay to the S or P state is equally probable (it is downhill either way). This is called the transition state.  The transition state is not a chemical species with any significant stability and should not be confused with a reaction intermediate (such as ES or EP). © 2008, YCMOU. All Rights Reserved.17

18. School of Science and Technology, Online Counseling Resource… How Enzymes Work-9  It is simply afleeting molecular moment in which events such as bond breakage, bond formation, and charge development have proceeded to the precise point at which decay to either substrate or product is equally likely.  The difference between the energy levels of the ground state and the transition state is the activation energy, G‡.  The rate of a reaction reflects this activation energy: a higher activation energy corresponds to a slower reaction. © 2008, YCMOU. All Rights Reserved.18

19. School of Science and Technology, Online Counseling Resource… Active site-1  The active site of an enzyme is the region that binds the substrates (and the cofactor, if any).  It also contains the residues that directly participate in the making and breaking of bonds.  These residues are called the catalytic groups.  In essence,the interaction of the enzyme and substrate at the active site promotes the formation of the transition state.  The active site is the region of the enzyme that most directly lowers the D G of the reaction, which results in the rate enhancement characteristic of enzyme action. © 2008, YCMOU. All Rights Reserved.19

20. School of Science and Technology, Online Counseling Resource… Active site-2  Although enzymes differ widely in structure, specificity, and mode of catalysis, a number of generalizations concerning their active sites can be stated: The active site is a three-dimensional cleft formed by groups that come from different parts of the amino acid sequence The active site takes up a relatively small part of the total volume of an enzyme. Active sites are clefts or crevices. Substrates are bound to enzymes by multiple weak attractions. The specificity of binding depends on the precisely defined arrangement of atoms in an active site. © 2008, YCMOU. All Rights Reserved.20

21. School of Science and Technology, Online Counseling Resource… Lock-and-Key Model of Enzyme-Substrate Binding  Emil Fischer's analogy of the lock and key expressed in 1890, has proved to be highly stimulating and fruitful.  Because the enzyme and the substrate interact by means of short-range forces that require close contact, a substrate must have a matching shape to fit into the site.  However, we now know that enzymes are flexible and that the shapes of the active sites can be markedly modified by the binding of substrate. © 2008, YCMOU. All Rights Reserved.21

22. School of Science and Technology, Online Counseling Resource… Lock-and-Key Model of Enzyme-Substrate Binding © 2008, YCMOU. All Rights Reserved.22

23. School of Science and Technology, Online Counseling Resource… Induced-Fit Model of Enzyme-Substrate Binding  Induced fit, a mechanism was postulated by Daniel Koshland in 1958.  The enzyme itself usually undergoes a change in conformation when the substrate binds, induced by multiple weak interactions with the substrate.  Induced fit serves to bring specific functional groups on the enzyme into the proper position to catalyze the reaction.  The active sites of some enzymes assume a shape that is complementary to that of the transition state only after the substrate is bound. This process of dynamic recognition is called induced fit. © 2008, YCMOU. All Rights Reserved.23

24. School of Science and Technology, Online Counseling Resource… Induced-Fit Model of Enzyme-Substrate Binding © 2008, YCMOU. All Rights Reserved.24

25. School of Science and Technology, Online Counseling Resource… Induced-Fit Model of Enzyme-Substrate Binding  The conformational change also permits formation of additional weak bonding interactions in the transition state.  In either case, the new enzyme conformation has enhanced catalytic properties.  Induced fit is a common feature of the reversible binding of ligands to proteins.  Induced fit is also important in the interaction of almost every enzyme with its substrate. © 2008, YCMOU. All Rights Reserved.25

26. School of Science and Technology, Online Counseling Resource… What You Learn-1…  You have learnt : Enzymes accelerates the rate of reaction. The enzyme molecule is not permanently altered by the reaction. Enzyme catalyze both the forward and the reverse reaction. Enzymes are highly specific for the substrates they bind. Enzymes work by binding to substrate. ES and EP are transient complexes of the enzyme with the substrate and with the product. 26© 2008, YCMOU. All Rights Reserved.

27. School of Science and Technology, Online Counseling Resource… What You Learn-2… Enzymes accelerates the rate of reaction by lowering down activation energy of the transition state. The active site of an enzyme is the region that binds the substrates. Emil Fischer's lock and key model has proved to be highly stimulating and fruitful. Induced fit, mechanism was postulated by Daniel Koshland which explains that the enzyme itself usually undergoes a change in conformation when the substrate binds, 27© 2008, YCMOU. All Rights Reserved.

28. School of Science and Technology, Online Counseling Resource… Critical Thinking Questions 1.State the characteristics of enzymes? 2. What is activation energy? 3.Write a note on working of enzymes by giving different models? © 2008, YCMOU. All Rights Reserved.28

29. School of Science and Technology, Online Counseling Resource… Hints For Critical Thinking Question 1.Catalyst, specificity, characters of enzyme molecule, forward and backward reaction and active site. 2.Energy required for reaction to occur. Role provided by enzyme lowering activation energy 3.Formation of enzyme substrate complex and enzyme product complex; lock and key model and induced fit model © 2008, YCMOU. All Rights Reserved.29

30. School of Science and Technology, Online Counseling Resource… Study Tips:1  Book1 Title: Molecular Cell Biology Author: Harvey Lodish, David Baltimore Publisher:Publishers: W. H. Freeman and Company  Book2 Title: Principles of Biochemistry Author: AlbertL Lehninger Publisher:CBS Publishers & Distributors 30© 2008, YCMOU. All Rights Reserved.

31. School of Science and Technology, Online Counseling Resource… Study Tips:2  Book3 Title: Biochemistry Author: Lubert stryer Publishers: Freeman International  Book4 Title: Biochemistry Author: Keshav Trehan Publishers: Wiley Eastern 31© 2008, YCMOU. All Rights Reserved.

32. School of Science and Technology, Online Counseling Resource… Study Tips www.en.wikipedia.org Microsoft Encarta Encyclopedia http://en.wikipedia.org/wiki/ Wikipedia the free encyclopedia (www.chem.qmul.ac.uk/iubmb/enzyme). 32© 2008, YCMOU. All Rights Reserved.

33. School of Science and Technology, Online Counseling Resource… End of the Presentation Thank You! 33© 2008, YCMOU. All Rights Reserved.