1. Enzymes Structure and function

2. Enzymes Over 1000 different reactions can take place in a single cell in any given moment. Each individual reaction is catalysed by a specific enzyme. Enzymes are very specific. A reaction occurs when chemical bonds of inputs or reactants are broken and the atoms recombine to form a new substance or substances.

3. Biochemical Pathways All metabolic reactions that occur in cells are controlled and regulated to maintain cell functions and to meet the energy needs of a cell. Done through biochemical pathways. Each step controlled by an enzyme.

4. Enzymes and their substrates A+B (substrates) = C+D (products) The compound acted upon by an enzyme is called a substrate. Enzymes are highly specific in their action – each enzyme acts on a particular substrate. The compounds obtained as a result of the enzyme action are called the products.

5. Enzymes and their substrates For A+B to equal C+D a certain amount of energy is required before this reaction can occur. Called activation energy. For cells to continue functioning enough energy must be provided to maintain the process of generating products from reactants & must control rate of energy released so they do not burn up.

6. Biochemical reactions go through a series of steps where the product of one step becomes the reactant for the next step  the product from one reaction is continually removed by being the reactant for the next reaction.

7. Enzyme function Cells use enzymes to speed up reactions Enzymes interact with substrate molecules (reactants) to increase rate of reaction. Enzymes are not consumed in a reaction and therefore can be recycled. Without enzymes the reactions that occur in living organisms would be so slow and hardly work at all.

8. Naming Enzymes Intracellular enzymes: speed up and control metabolic reactions inside the cell. Extracellular enzymes: secreted from cell and catalyse reactions outside the cell. Named by attaching ‘– ase’ to the substrate on which it acts. Carbohydrases act on carbohydrates Lipases act on Lipids Proteases acts on Protein Nucleases act on nucleic acids ATPase acts on ATP

9. Enzyme Power Work fast Catalase is one of the fastest Found in liver where it speeds up the breakdown of hydrogen peroxide (H 2 O 2 ) into oxygen and water. 2 H 2 O 2  2H 2 O + O 2 (balanced equation)

10. Catalase reduces the activation energy needed to break down hydrogen peroxide. Enzymes are powerful because they reduce the activation energy for chemical reactions.

11. Structure of Enzymes Enzymes are made up of proteins. The basic building blocks of proteins is the amino acid. There are 20 different amino acids and various combinations make up the different proteins, including enzymes, in living organisms.

12. Structure of Enzymes The folding of an enzyme protein into its tertiary structure forms an actual groove or pocket. This grove can accommodate one or more substrate molecules called an active site. Active site = highly specific for a particular substrate & needs to be a compatible shape for binding to occur.

13. Enzyme action This complementary fitting of shapes is often called the ‘lock-and-key’ theory of enzyme action. In some cases, the shape of the active site of the enzyme varies slightly from that of the substrate and the two fit only after contact, when the substrate includes a complementary shape at the active site of the enzyme. This is the ‘induced-fit’ theory of enzyme action.

14. Lock-and-key & Induced-fit models

15. Cofactors and Coenzymes Many enzymes require the presence of other factors as well as the protein part before they can act. Cofactors: small inorganic substances (e.g. zinc ions and magnesium ions) that need to be present in addition to an enzyme to catalyse a certain reaction Coenzymes: non-protein organic substances that are required for enzyme activity (eg. vitamin). Small molecules compared to the enzyme Major role in metabolic pathways Can function as a carrier, donor or acceptor of a substance involved in the reaction and/or may bind with an enzyme to activate it.

16. Factors affecting enzyme activity The rate of an enzymatic reaction is affected by several factors, including: pH temperature enzyme concentration substrate concentration inhibition

17. Temperature Work best in temperatures that they are found. Human body = 37 ˚C Enzymes require less energy to work due to their flexible structure.

18. Temperature How does temperature change affect enzyme activity? Increase in temp = increase in activity Increase in activity = increase in collisions between substrate and enzyme  faster rate of reaction. If temperature is too high, bonds break and the protein loses it’s functional shape (becoming permanently denatured). The enzyme can no longer bind with the active site of the substrate. Enzymes are not denatured at low temperatures.

19. Effect of pH Each enzyme has an optimum pH at which it works. Most work effectively at pH7 (neutral) Optimal pH of an enzyme relates to the environment in which it works. E.g. pepsin in the stomach (pH 2). Catalase works in a neutral environment of cells in the liver (pH 7). Alkaline phosphatase in bone (pH 9.5).

20. Effect of pH A change in pH from the optimum can change the shape of an enzyme and affect its ability to combine with its substrate. Because the enzyme is less able to combine with its substrate, it is unable to act and the rate of the metabolic reaction declines.

21. Enzyme concentration Only a very small number of enzyme molecules are usually involved in a reaction and these produce a given amount of product per unit time. If the amount of enzyme is increased, the amount of product made per unit time increases. Will there be a change in the total amount of product made? Enzyme molecules are not used up in a reaction and are available for reuse.

22. Substrate concentration Amount of substrate or enzyme present in a reaction mix can limit the amount of product produced. Increased substrate  more products made until all enzyme molecules are working at their maximum capacity. The addition of more substrate to an enzyme solution will initially increase the rate of the reaction if not all active sites of the enzyme present are occupied.

23. Substrate concentration However, the enzyme solution contains a set amount of enzyme, and if no more is added, the rate of the reaction tapers off as all the active sites of the enzyme molecules become occupied.

24. Inhibiting the work of enzymes Some enzymes have 2 or more active sites for enzymes Activity of almost every enzyme in a cell is regulated by feedback inhibition where the product of the reaction can inhibit enzyme activity. Inhibitor binds to enzyme  active site changing shape, therefore cannot bind to substrate.

25. Inhibitors Non-competitive inhibitor: a molecule that binds to an enzyme at a site other than the active site which changes the shape of the enzyme so that the substrate can no longer bind to the active site. Competitive inhibitor: a substance that competes with a substrate for an enzyme’s active site. Examples: poisons whereby the inhibitor binds to the active site preventing the enzyme from catalysing reactions and overtime this concentration of enzyme reduces and the reactions stop.