Enzymes.pptx

Enzymes

1. BY Assist. Prof. Dr.Berciyal Golda. P VICAS

2. INTRODUCTION Enzymes   are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which  enzymes  may act are called substrates, and the  enzyme  converts the substrates into different molecules known as products .

3. The biological processes that occur within all living organisms are chemical reactions, and most are regulated by enzymes. Without enzymes, many of these reactions would not take place at a perceptible rate. Enzymes catalyze all aspects of cell metabolism. This includes the digestion of food, in which large nutrient molecules (such as proteins, carbohydrates, and fats) are broken down into smaller molecules; the conservation and transformation of chemical energy; and the construction of cellular macromolecules from smaller precursors.

4. Enzymes are proteins that increase the rate of reaction by lowering the energy of activation • They catalyze nearly all the chemical reactions taking place in the cells of the body • Enzymes have unique three-dimensional shapes that fit the shapes of reactants ( substrates)

5. What is an enzyme? An enzyme is a substance that acts as a  catalyst  in living organisms, regulating the rate at which  chemical reactions  proceed without itself being altered in the process. • Enzymes are biological catalysts. • A Catalyst is defined as "a substance that increases the rate of a chemical reaction without being itself changed in the process.”

6. ENZYM E S DEFINITION Enzymes are proteins that function as biological cata l y st s . A cata l y st i s a su b stan c e tha t speeds u p a chemical reaction but isn’t changed by the reaction. Enzymes catalyze all aspects of cell metabolism.

7. Enzymes are highly specific to the reactions they catalyze The y al t er or speed u p th e r a t es of chemical reactions that occur in a cell. The y r emain unchan g ed af t er a chemical reaction. They are affected by temperature. They are affected by pH. They catalyze reversible reactions. PROPERTIES OF ENZYMES

8. Catalytic efficiency – high efficiency , 10 3 to 10 17 faster than the corresponding un-catalyzed reactions S p ec i f i c i t y - h i gh s p ec i f i c i t y , i n t e r ac t i ng w i t h on e o r a f e w specific substrates and catalyzing only one type of c h e m i ca l r eac t i on . Mild reaction conditions- 37℃, physiological pH, ambient a t m o s ph e r i c p r ess u r e

9. C h e m i c a l c o m p o s i t i o n o f e n z y m e s Simple protein Conjugated protein H o l o e n z y me = A po e n z y me + C o fa ct o r C o enz y m e : l oos ely b o und t o enz y m e ( n o n- covalently bound). Prosthetic group : very tightly or even c ova len t ly b o und t o enz y m e ( c ova len t ly b o un d ) Cofactor

10. Classification of enzymes Based on their their composition Monomeric enzyme: Monomeric enzymes are enzymes consisting of a single polypeptide chain or subunit. The proteins in the  monomeric  units are made of polymers of aminoacids .

11. 2. Oligomeric enzyme: Oligomeric enzymes consist of two or morepolypeptide chains which are usually linked toeach other by non covalent interactions andnever by peptide bonds. The componentpolypeptide chains are termed sub-units andmay be identical ,they are some times calledprotomers .

12. 3.Mu l ti e nz y m e com p le x : A  multienzyme complex contains several copies of one or several enzymes (polypeptide chains) packed into one assembly.  Multienzyme complex carries out a single or a series of biochemical reactions taking place in the cells. It allows to segregate certain biochemical pathways into one pace in the cell.

13. Nomenclature Recommended name E n z y m e s a re u s u a lly n a me d a cc o r d i ng to t he reaction they carry out. T o g e n e r a te the n a m e o f a n e n z y me , the suffix ase is added to the name of its substrate ( e g , lactase is the enzyme that cleaves lactose) or the type of reaction ( e.g. , DNA polymerase forms DNA polymers). Systematic name (International classification) By the reactions they catalyze (Six classes)

14. DISTRIBUTION Enzymes are not randomly distributed but are spec i f ical l y loca t ed i n side th e c ells f or e x ample Digestive Enzymes: (Pancreas and stomach) Glycosol : ( oxidation of glucose) Mitochondria TCA cycle

15. How enzymes work Enzymes lower a reaction’s activation energy All chemical reactions have an energy barrier , called the activation energy, separating the reactants and the products. activation energy: amount of energy needed to disrupt stable molecule so that reaction can take place.

16. Enzymes Lower a Re a c ti on ’ s Ac ti va ti o n Energy

17. What is the difference between an enzyme and a protein? Protein A ll e n z y me s a re p r o t ei ns e x c e p t s o m e R NA s not all proteins are enzymes RN A Enzymes

18. The active site of the enzyme E n z y m es b in d s ub s t r a t es t o th e i r a c t i v e s i t e a n d stabilize the transition state of the reaction. The active site of the enzyme is the place where the substrate binds and at which catalysis occurs . T h e a c t i v e s i t e b in d s t h e s ub s t r a t e, f o rm i n g an enzyme-substrate(ES) complex. Binding site Active site Catalytic site

19. Enzymatic reaction steps Substrate approaches active site Enzyme-substrate complex forms Substrate transformed into products Products released Enzyme recycled

20. Enzymes in clinical diagnosis An enzyme test is a blood test or urine test that measures levels of certain enzymes to assess how well the body’s systems are functioning and whether there has been any tissue damage .

21. Common enzymes used for clinical diagnosis alanine aminotransferase ( ALT,also called glutamate pyruvate transaminase,GPT ) alkaline phosphatase amylase aspartate aminotransferase creatine kinase lactate dehydrogenase

22. GROUPS OF ENZYMES THERE ARE SIX MAJOR GROUPS OF ENZYMES

23. ENZYME PORTIONS Enzymes are composed of: APO ENZYME : Protein portion consisting of amino acid chains CO- FACTORS activate enzymes and are not protein parts . HOLOENZYME (conjugated enzyme) Both cofactors and apo enzymes help to form a conjugated enzyme called holoenzyme.

24. 3. SUBSTRATE AND ACTIVE SITE : Enzymes operate by binding to a substrate The catalytic (active) site is the portion of the enzyme where substrate binding occurs.

25. MECHANISM OF ENZYME ACTION Proposed by Emil Fischer (1894): the shape of the substrate and the active site of the enzyme are thought to fit together like a key into its lock. I t w as sug g es t ed b y Arrhenius that the shape of the Active Sites of Enzymes is exactly Complementary to the shape of the Substrate . 1. THE LOCK-AND-KEY HYPOTHESIS

26. 2. Induced fit hypothesis proposed in 1958 by Daniel E. Koshland , Jr.: the binding of substrate induces a conformational change in the active site of the enzyme. In addition, the enzyme may distort the substrate, forcing it into a conformation similar to that of the transition state A more recent model suggested by Daniel Koshland the Induced- Fit Model. It states that the shape of Active Sites are not exactly Complementary, but are changed according to the substrate molecules

27. For example, the binding of glucose to hexokinase induces a conformational change in the structure of the enzyme such that the active site assumes a shape that is complementary to the substrate (glucose) only after it has bound to the enzyme.

28. Factors affecting enzyme activity Concentration of substrate Concentration of enzyme Temperature pH Activators Inhibitors

29. FACTORS AFFECTING THE RATE OF ENZYME ACTIONS 1. TEMPERATURE Enz y me s h av e an o p tim u m t em p e r atu r e at w hich the y w o r k fastest. Up to the optimum temperature the rate increases Above the optimum temperature the rate decreases

30. 2. pH Enzymes have an optimum pH at which they work fastest. F or mos t enz y me s thi s i s about pH 7-8 but a few enzymes can work at extreme pH, such as p r o t ease enz y me s i n an i ma l s t omach s , w hich h a v e an optimum of pH 1.

31. 3. ENZYME CONCENTRATION As the enzyme concentration increases the rate of the reaction increases linearly At very high enzyme concentration the substrate concentration may become rate-limiting

32. 4. SUBSTRATE CONCENTRATION As the substrate concentration increases, the rate increases because more substrate molecules can collide with enzyme molecules, so more reactions will take place

33. INHIBITION CAN BE EITHER COMPETITIVE OR NONCOMPETITIVE 1. COMPETITIVE INHIBITION: Competitive inhibition is the interruption of an enzyme's ability to bind to a substrate due to a different molecule binding to the active site.

34. 2. NON COMPETITIVE INHIBITION : Non competitive inhibitors are not similar to the substrate and they do not bind to the active site of the enzyme. They change the conformation of the active site.

35. ROLE OF ENZYMES IN THE BODY DEGRADATION REACTIONS (CATABOLIC) SYNTHESIS (ANABOLIC) DIGESTION Enzymes are used f or a wi d e v arie t y of purposes, such as in digestion. PROTECTION Enzymes are also used in protection against Pathogens. They can be used to destroy invading Microorganisms.