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enzymes.ppt
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- 2. Of all thefunctions of proteins, one of the most important is that of catalysis In the absence of catalysis, most reactions in biological systems would take place far too slowly to provide products at an adequate pace for metabolising organisms The catalysts that serve this function in living organisms are called ENZYMES All enzymes are globular proteins and are the most efficient catalysts known Enzymes are able to increase the rate of reaction by a factor of up to 1020 over uncatalysed reactions.
- 3. Characteristics of Enzymes Theyare proteins of high molecular weight They are biological catalysts They are sensitive to temperature changes - being denatured at high temperatures They are sensitive to pH They are generally specific in the reactions they catalyse Enzymes possess an active site within which chemical reactions take place Substrate molecule in the ACTIVE SITE Enzyme molecule
- 4. The Active Site Substrate molecules (complementary shapeto active site) Enzyme molecule Product molecules diffuse away from the active site Substrate molecules bind with enzyme molecules at the active site as a consequence of their complementary shapes. This is the basis of the LOCK AND KEY MODEL of enzyme activity Enzyme remains unchanged Active site Reaction occurs
- 5. The Lock AndKey Model In an enzyme - catalysed reaction, the enzyme binds to the substrate to form a complex An enzyme - substrate complex forms A reaction occurs forming an enzyme - product complex Products diffuse away from the active site Enzyme molecule The lock & key model proposes that the substrate binds to the active site which it fits exactly, like a key in a lock S
- 6. The Induced FitModel This model takes into account the fact that proteins (enzymes) have some three-dimensional flexibility SUBSTRATE Substrate binds to the enzyme at the active site Binding of the substrate induces the enzyme to change shape such that there is an exact fit once the substrate has bound Enzyme Molecule According to this model, reactions can only take place AFTER induced fit has occurred
- 7. Energy level of substrate Energylevel of the products Energy barrier without enzyme Energy barrier with enzyme Lower activation energy Enzymes are catalysts because they lower the ACTIVATION ENERGY needed to drive a reaction Substrates need to overcome an energy barrier before they will convert to products
- 8. Factors Affecting TheRate Of Enzyme Catalysed Reactions Temperature pH Substrate Concentration Enzyme Concentration Inhibitors Activators
- 9. Molecules are constantly inmotion and colliding with one another. The speed of motion and number of collisions is affected by the temperature AT LOW TEMPERATURES AT HIGHER TEMPERATURES More enzyme-substrate complexes and hence more product molecules are formed at the higher temperature
- 10. Temperature and EnzymeActivity Rate of Reaction Temperature (oC) As the temperature increases, molecular motion and thus molecular collisions increase. More product molecules are formed in a given time and hence the reaction rate increases For many enzymes, the maximum rate of reaction is reached at a temperature around 37 to 40oC. This is the optimum temperature. The reaction rate doubles for every 10oC rise in temperature As the temperature increases beyond the optimum, bonds that stabilise the enzyme’s tertiary structure are broken. The enzyme loses its shapes and the active site is altered. Substrate can no longer bind to the enzyme. The enzyme has been DENATURED
- 11. In the temperaturerange 4oC to 40oC, the rate of reaction doubles for every 10oC rise in temperature The temperature coefficient (Q10) is the effect of a 10oC rise in temperature on the rate of a chemical reaction When the rate of reaction doubles for every 10oC rise in temperature then the Q10 = 2 For an enzyme controlled reaction, in the temperature range 4oC to 40oC, an increase of 10oC doubles the rate of reaction. Therefore the Q10 = 2 Temperature and Enzyme Activity
- 12. Enzymes and pH INCREASINGACIDITY INCREASING ALKALINITY 1 3 0 2 4 5 6 7 8 9 10 11 12 13 14 The acidity of a solution is measured by the concentration of hydrogen ions (H+) and is expressed in terms of pH The pH scale ranges from 0 to 14 Pure water has a pH of 7.0, which is the pH of a neutral solution with equal numbers of H+ and OH- ions If an acid is added to pure water, the hydrogen ion concentration increases, causing the solution to become acidic, which is measured as a lower pH If a base is added to pure water, the hydrogen ion concentration decreases and the hydroxyl ion (OH-) concentration increases. The solution becomes more basic (alkaline) and is measured as a higher pH NEUTRAL
- 13. Each specific enzymecan only work over a particular range of pH Each enzyme has its own optimum pH where the rate of reaction is maximum The effects of pH on the rate of enzyme controlled reactions display characteristically bell shaped curves A B C Enzyme A = amylase optimum pH = 7.2 Enzyme B = pepsin optimum pH = 2.0 Enzyme C = lipase optimum pH = 9.0 Changes in pH can affect the ionic and hydrogen bonds responsible for the specific tertiary shape of enzymes. Extremes of pH break these bonds and denature the enzyme Enzymes and pH
- 15. Naming Enzymes Enzymes areclassified according to the type of chemical reaction that they catalyse HYDROLASES are enzymes that catalyse hydrolysis reactions maltose is a disaccharide consisting of two alpha glucose molecules joined by a glycosidic bond maltase is a hydrolase enzyme that catalyses the hydrolysis of maltose into two glucose molecules H2O MALTASE
- 16. TRANSFERASES are enzymesthat catalyse reactions involving the transfer of atoms or groups of atoms from one molecule to another During cellular respiration, a phosphate group is transferred from a molecule of ATP to a glucose molecule This process activates the glucose P P A P three phosphate groups ATP ADENOSINE TRIPHOSPHATE The type of enzyme that catalyses this reaction is a TRANSFERASE Glucose Phosphate ADP ADENOSINE DIPHOSPHATE + Glucose P Naming Enzymes
- 17. OXIDOREDUCTASES are enzymesthat catalyse reactions involving oxidation and reduction What is Oxidation? Oxidation reactions can occur in three main ways: •addition of oxygen •removal of hydrogen atoms •removal of electrons What is Reduction? Oxidation reactions can occur in three main ways: •removal of oxygen •addition of hydrogen atoms •addition of electrons Naming Enzymes
- 18. EXAMPLES OF OXIDATIONAND REDUCTION C + O2 CO2 Oxidation Fe3+ + e- Fe2+ Reduction NAD + 2H NADH2 Reduction The enzymes that catalyse the above reactions are classed as OXIDOREDUCTASES OXIDOREDUCTASES PLAY AN IMPORTANT ROLE IN THE BIOCHEMISTRY OF RESPIRATION Naming Enzymes
- 19. OXIDOREDUCTASES AND RESPIRATION Duringthe process of respiration, a cycle of reactions, called The Krebs Cycle takes place The molecules shown in the cycle are organic acids The cycle involves the stepwise oxidation of a 6 carbon acid in to a 4C acid Oxidation in the cycle involves the removal of pairs of hydrogen atoms from the acids NADH2 2H The class of oxidoreductase that catalyses such a reaction is a DEHYDROGENASE The hydrogen atoms are then accepted by the hydrogen carrier NAD This example illustrates the point that when one substance is oxidised another is reduced The organic acid is oxidised and NAD is reduced Such reactions are called REDOX REACTIONS Naming Enzymes
- 20. Metabolic Pathways and FeedbackInhibition Metabolic pathways are sequences of chemical reactions each controlled by a specific enzyme A D B C E enzyme 1 enzyme 2 enzyme 3 enzyme 4 The initial substrate into the final product is converted by a series of intermediate compounds It is wasteful for a sequence of chemical reactions to continue if the end product is being produced at a rate surplus to requirements When the end product of the pathway begins to accumulate, it may act as an inhibitor of the first enzyme in the pathway Further production of the end product is prevented in a process called FEEDBACK INHIBITION INHIBITS
- 22. The Effect OfSubstrate Concentration On The Rate Of Enzyme - Catalysed Reactions Low Substrate Concentration Low product concentration per unit time Increased Substrate Concentration More product formation; increased reaction rate
- 23. Further increase in substrate concentration Excesssubstrate concentration Maximum product formation; maximum rate of reaction No further increase in product formation; maximum reaction rate maintained Enzyme concentration is the LIMITING FACTOR The Effect Of Substrate Concentration On The Rate Of Enzyme - Catalysed Reactions
- 24. The Effect OfSubstrate Concentration On The Rate Of Enzyme - Catalysed Reactions Increasing concentration of substrate Rate of reaction A Rate of reaction increases as the substrate concentration increases Rate of reaction reaches a maximum at substrate concentration A No further increase in the reaction rate despite the increasing substrate concentration All the active sites of the enzymes are occupied - Enzyme concentration is the limiting factor
- 25. The Effect OfEnzyme Concentration On The Rate Of Enzyme - Catalysed Reactions Rate of reaction Increasing concentration of enzyme The rate of reaction is directly proportional to the enzyme concentration As enzyme concentration increases, the rate of reaction increases In living cells, enzyme concentrations are usually much lower than substrate concentrations Substrate concentration is rarely a limiting factor
- 26. The Effect OfReversible Inhibitors On Enzyme Activity The presence of inhibitor molecules decreases the rate of enzyme reactions by reversible combination with the enzyme Normal substrate Molecule similar in shape to the normal substrate This molecule competes with the normal substrate for the active site This molecule is an example of a COMPETITIVE INHIBITOR
- 27. The Effect OfReversible Inhibitors On Enzyme Activity Normal substrate converted into products This inhibitor molecule attaches to the enzyme at a position away from the active site The substrate molecule can still bind to the active site Substrate cannot be converted into product. The inhibitor molecule changes the shape of the active site preventing induced fit This inhibitor is a NON-COMPETITIVE INHIBITOR This inhibitor is not competing for the active site
- 28. The Effect OfCompetitive Inhibitors On Enzyme Activity Low substrate concentration Inhibitor molecule When the substrate concentration is low, the inhibitor competes successfully for the active site. Fewer substrate molecules are converted into product and the rate of reaction is reduced
- 29. The Effect OfCompetitive Inhibitors On Enzyme Activity High substrate concentration Inhibitor molecule The effect of the competitive inhibitor is overcome when the high concentration of substrate molecules compete successfully for the active sites of the enzymes: At high substrate concentration, maximum reaction rate is achieved
- 30. maximum rate without inhibitor inhibitor present The effectof the inhibitor is overcome by very high substrate concentrations At high substrate concentrations, the inhibitor is out-competed by the substrate and the maximum rate of reaction is achieved At low substrate concentrations, the rate of reaction is reduced in the presence of the inhibitor The Effect Of Competitive Inhibitors On Enzyme Activity
- 31. substrate binds tothe enzyme when a non-competitive inhibitor is present but cannot be converted to product - The rate of reaction is reduced The Effect Of Non-Competitive Inhibitors On Enzyme Activity Low substrate concentration Inhibitor molecule substrate molecules not converted to product when inhibitor molecules are bound to the enzyme substrate molecules converted into product when no inhibitor is attached to the enzyme
- 32. Inhibitor molecule substrate moleculesconverted into product when no inhibitor is attached to the enzyme At high substrate concentration all enzyme active sites are occupied. Substrate molecules bound to enzymes with attached inhibitor are NOT converted into product - Maximum reaction rates are never achieved The effect of the inhibitor is not overcome by increasing the substrate concentration. All the enzyme molecules with bound non-competitive inhibitor do NOT convert substrate to product. The effect is equivalent to lowering enzyme concentration High substrate concentration X X X X X X The Effect Of Non-Competitive Inhibitors On Enzyme Activity
- 33. no inhibitor; maximum reactionrate achieved at high substrate concentration with inhibitor; maximum reaction rate never achieved - the effect of the inhibitor cannot be overcome by increasing the substrate concentration The Effect Of Non-Competitive Inhibitors On Enzyme Activity Non-competitive inhibitors act by preventing bound substrate being converted into product