Enzymes

1. Enzymes Chapter 5

2. Lesson Objectives • Questions to answer! • What are enzymes? • State the definition of enzymes. • How do enzymes work? • Explain the mode of action of enzymes in terms of active site, enzyme-substrate complex, lowering of activation energy, and enzyme specificity. • Describe the characteristics of enzymes. • 3. What affects enzyme activity? • Investigate and explain the effects of temperature, pH, on the rate of enzyme-catalyzed reactions. • Where are enzymes used? • State 1 enzyme-catalyzed process. • Classify enzymes.

3. What are enzymes? What are catalysts? How do they work? Recall: What are proteins?? Properties of enzymes Definition of Enzymes Enzymes are biological catalysts, commonly made of protein. They alter the rate of chemical reactions without themselves being chemically changed at the end of the reaction.

4. What are enzymes? Recall: Proteins • Basic unit of proteins: • How amino acids are linked up: • Link between amino acids: • Long chains of basic units: • Polypeptides are folded and its 3D shape is held together by . • Weak bonds can be broken by heat and chemicals. The protein is said to be . • A denatured protein loses its . amino acids condensation reaction peptide bond polypeptide weak bonds denatured function Source: http://www.monroecc. edu/deps/pstc/backup/heme.gif

5. How do enzymes work? Enzymes are Biological Catalysts • A catalyst is a substance which can alter or speed up a chemical reaction. • Catalysts are not chemically-changed at the end of the reaction.

6. How do enzymes work? Enzymes are Biological Catalysts Eg: Decomposition of Hydrogen Peroxide… 2H2O2→ 2H2O + O2 This reaction can be sped up by a catalyst, manganese (IV) oxide. Videos: Dilute H2O2: H2O2 decomposition Fresh H2O2: Last High School Chemistry Class Source: http://pics.drugstore. com/prodimg/73864/200.jpg

7. How do enzymes work? Inorganic Catalyst Enzymes are Biological Catalysts Eg: Decomposition of Hydrogen Peroxide… 2H2O2→ 2H2O + O2 This reaction can be sped up by a catalyst, manganese (IV) oxide. 2H2O2 2H2O + O2 + Heat The same amountof manganese (IV) oxide remains after the reaction. It is not changed during the reaction. MnO2 (catalyst)

8. How do enzymes work? Biological Catalyst (Organic) Enzymes are Biological Catalysts The enzyme CATALASE can speed up hydrogen peroxide decomposition. Enzymes are BIOLOGICAL CATALYSTS. Video: Nosebleed Chemistry 2H2O2 2H2O + O2 + Heat Note: Catalase is also found in potatoes! Catalase (enzyme) How do enzymes work?

9. How do enzymes work? Activation Energy • The energy needed to start a chemical reaction is called activation energy. • Once the reaction has received enough energy, the rest of the reaction occurs spontaneously.

10. How do enzymes work? Products Reactants Activation Energy • Enzymes lower the activation energy required to start a chemical reaction. • Enzymes do not change the energy level of reactants and products. • Enzymes only lower the ‘height’ of the ‘activation energy hill.’

11. How do enzymes work? active sites enzyme molecule (the ‘lock’) enzyme molecule is free to take part in another reaction B AB A enzyme-substrate complex substrate molecules (A and B) can fit into the active sites a new substance (product) AB leaves the active sites Lock and Key Hypothesis • The substances on which enzymes act are called substrates. • Enzymes bind to substrates by the lock and key hypothesis.

12. How do enzymes work? Lock and Key Hypothesis • Enzyme reaction depends on the presence of active sites. • Active sites have a specific 3D shape. • Specific substrate molecules fit into the active site like a lock and key. • Substrate binds to the enzyme, forming an enzyme substrate complex. • Reactions take place at the active sites to convert substrate molecule(s) into product molecule(s). • Product molecule(s) separate, leaving the enzyme molecule unchanged and free to combine again with more substrate molecules.

13. How do enzymes work? Lock and key hypothesis Induced Fit Model Induced Fit Model • Current hypothesis for enzyme action • When a substrate molecule fits into an enzyme molecule, the enzyme molecule alters its shape slightly so that it fits more tightly around the substrate molecule. • This makes the chemical reaction easier. Source: http://neurobio.drexel.edu/GalloWeb/loudon_enzymes.htm

14. How do enzymes work? Enzyme Characteristics Enzymes are required in minute amounts • Enzymes are very efficient molecules. • They remain unchanged at the end of the reaction, and thus can be reused over and over again. • A of enzyme can catalyze a of chemical reactions. small amount large amount

15. How do enzymes work? Enzyme Characteristics Enzyme Specificity • Enzyme action is highly specific: each chemical reaction is catalyzed by a unique enzyme. • The enzyme’s specificity is due to its 3-dimensional surface configuration. • The shape of the substrate must be complementary to the shape of the enzyme’s active site. • The shape of an enzyme can be affected by high temperature and acids and alkalis.

16. How do enzymes work? Enzyme Characteristics Enzymes catalyze reversible reactions • Some reactions in living cells are reversible. They can proceed in the forward or backward direction. • Some enzymes catalyze both forward and backward reactions until an equilibrium is reached. This occurs when the amount of reactants equals the amount of products formed.

17. How do enzymes work? Enzyme Characteristics Some enzymes require coenzymes • Some enzymes require a coenzyme (another compound) to be bound to them before they can catalyze reactions. • Coenzymes are non-protein organic compounds. • Eg. of coenzymes: Vitamin B complex

18. What affects enzyme activity? 4 Factors Enzymes are affected by the following: • Temperature • pH • Enzyme concentration • Substrate concentration

19. What affects enzyme activity? Temperature • Enzymes have an optimum temperature. • This is the temperature at which the enzyme catalyzes the largest number of reactions per second. • The optimum temperature of enzymes varies in different organisms, and is often but not always close to the temperature at which the enzyme usually functions. • Some enzymes may have very high or very low optimum temperatures.

20. What affects enzyme activity? The optimum temperature is reached. Enzyme is most active. 3 Beyond the optimum temperature, enzyme activity decreases. 4 As the temperature rises, enzyme activity increases as indicated by the increase in the rate of reaction it catalyses. Usually the enzyme is twice as active for every 10°C rise in temperature until the optimum temperature is reached. 2 At point D, the enzyme has lost its ability to catalyse the reaction. 5 1 An enzyme is less active at very low temperatures. Temperature Rate of reaction (enzyme activity) 0 K (optimum temperature) D Temperature

21. What affects enzyme activity? Temperature As temperature rises… • Particles of matter are in constant random motion. • In the reaction, the enzyme and substrate molecules move and collide with one another at random. • Raising the temperature increases the kinetic energy of the molecules. • The substrate and enzyme molecules collide with each other more often, increasing the chance of substrates fitting into active sites. • The rate of formation of enzyme-substrate complex increases, increasing the rate of formation of products.

22. What affects enzyme activity? Temperature As temperature rises… • Enzyme activity increases as the temperature increases up to the optimum temperature. • At high temperatures, enzyme activity decreases. • Enzymes are made of , and its 3D shape are held together by . • At high temperatures, the vibrations of the atoms in the enzyme vibrate so violently that they break the weak bonds in the enzyme. • The enzyme loses its shape and becomes denatured. • The higher the temperature, the faster the rate of denaturation. proteins weak bonds

23. What affects enzyme activity? pH • Enzymes are affected by the acidity or alkalinity of the solutions they are in. • Acid or alkali can interact with the enzyme molecule, causing the protein to change its shape. • Extreme changes in pH of the solutions denature the enzymes. • Enzymes also have an optimum pH – the pH at which the enzyme can best function in.

24. What affects enzyme activity? pH

25. What affects enzyme activity? Enzyme & Substrate Concentration

26. What affects enzyme activity? Enzyme & Substrate Concentration • In a solution of fixed enzyme concentration, as substrate concentration increases, the rate of reaction increases to a maximum. • Beyond the maximum point, increasing the substrate concentration will not increase the rate of reaction. • This is because at any point of time, all the enzyme molecules are in use. The enzyme molecules are saturated. • The enzyme concentration becomes the limiting factor. • The reaction rate will increase if the enzyme concentration is increased.

27. Where are enzymes used? Digestion • Some food molecules are large and insoluble in water. • These food molecules cannot through the cell surface membrane. • Some examples of large food molecules are , and . • The large molecules must first be converted into simpler smaller substances which are soluble in water and diffusible. • This is known as digestion, and is achieved by digestive enzymes. diffuse proteins starch fats

28. Where are enzymes used? HYDROLYTIC REACTIONS CONDENSATION REACTION Digestion Enzymes are involved in two types of reactions in the body: • Synthesis of complex substances from simpler ones • Break down of complex substances to simpler ones • Examples of hydrolysis in the body: • Large molecules of food are converted to smaller molecules by digestive enzymes. • In cell respiration, glucose is broken down to carbon dioxide and water and release energy. • Hydrogen peroxide can be produced in chemical reactions in cells. It is toxic to tissues. Cells produce enzyme catalase which catalyses the breakdown of hydrogen peroxide. • Examples of condensation reactions in the body: • Forming from glucose • Forming proteins from starch amino acids Enzymes catalyze practically ALL the chemical reactions that occur in an organism!

29. Where are enzymes used? Classification of Enzymes • Enzymes are classified according to the chemical reactions they catalyze. • Enzymes that catalyze hydrolytic reactions are known as hydrolases. • Oxidation-reduction enzymes are involved in breaking down glucose during respiration. • Enzymes were previously named by the persons who discovered them. • Nowadays, enzymes are named according to a scientific system.

30. Where are enzymes used? Classification of Enzymes

31. Where are enzymes used? Industrial Uses • Enzymes are used in industry as they can bring about chemical changes at low temperature. • Chemical reactions at low temperatures are easier to control and cheaper to run. • Enzymes can be extracted from living cells and used in their pure form.

32. Where are enzymes used? Industrial Uses • Microorganisms producing useful enzymes can be used in industry to make cheese, yoghurt and beer. • Catalase can be added to latex containing hydrogen peroxide to produce oxygen to form foam rubber. • Enzyme specificity makes them ideal for use in analysing chemicals. • Enzymes can be used to detect glucose in urine. • This can help to detect diabetes. Source: http://news.thomasnet.com/ images/large/011/11187.jpg Source: http://www.southernbiological.com/Products/ Kits&Equipment/SpecialLabFieldEquipt/G10_36.htm

34. Pure Biology Chapter 5 Definition of enzymes Enzymes are biological catalysts, commonly made of protein. They alter the rate of chemical reactions without themselves being chemically changed at the end of the reaction. Enzymes have specific are Functions Proteins as Remain chemically unchanged at the end of the reaction Biological catalysts are form speed up affected by Enzyme-substrate complex Rate of reaction Inactivated Denatured Enzyme concentration Substrate concentration pH Temperature with the help of by at low at high by lowering are at extreme of Coenzymes Lock-and-key hypothesis Induced-fit model Activation energy Chemical reactions involve found in Intracellular enzymes Extracellular enzymes Digestive system examples is the Specific binding of enzyme Lipases Proteases Carbohydrases to digest digest digest Proteins Substrate Lipids Carbohydrates to form to form to form to form Specific product(s) Fatty acids and glycerol Amino acids Simple sugars

35. Pure Biology Chapter 5 Definition of enzymes Enzymes have specific are Functions as Remain chemically unchanged at the end of the reaction Biological catalysts are form speed up affected by Enzyme-substrate complex Rate of reaction Inactivated Denatured Enzyme concentration Substrate concentration with the help of by at low at high by lowering are at extreme changes of of Coenzymes Induced-fit model Chemical reactions involve found in Intracellular enzymes Extracellular enzymes examples is the Specific binding of enzyme Lipases to digest digest digest Proteins Substrate Carbohydrates to form to form to form to form Specific product(s) Simple sugars