End Show Slide 1 of 34 Copyright Pearson Prentice Hall Lecture :ch2–sec4 Chemical Reactions & Enzymes

End Show 2–4 Chemical Reactions and Enzymes Slide 2 of 34 Copyright Pearson Prentice Hall Chemical Reactions A chemical reaction is a process that changes one set of chemicals into another set of chemicals.

End Show 2–4 Chemical Reactions and Enzymes Slide 3 of 34 Copyright Pearson Prentice Hall Chemical Reactions Chemical reactions always involve changes in the chemical bonds that join atoms in compounds. –Breaking bonds releases energy –Forming bonds stores energy

End Show 2–4 Chemical Reactions and Enzymes Slide 4 of 34 Copyright Pearson Prentice Hall Energy in Reactions In order to stay alive, organisms need to carry out reactions that require energy. Because matter and energy are conserved in chemical reactions, every organism must have a source of energy to carry out chemical reactions. Plants get their energy from the sun. Animals get their energy from eating plants or other animals.

End Show 2–4 Chemical Reactions and Enzymes Slide 5 of 34 Copyright Pearson Prentice Hall Energy in Reactions Activation Energy ●Chemical reactions that release energy do not always occur spontaneously. ●Chemists call the energy that is needed to get a reaction started the activation energy. Jumping bean analogy Reactants Products Activation Energy Barrier

End Show 2–4 Chemical Reactions and Enzymes Slide 6 of 34 Copyright Pearson Prentice Hall Energy in Reactions Activation energy is a factor in whether the overall chemical reaction releases energy or absorbs energy. Ex: PhotosynthesisEx: Cellular respiration

End Show 2–4 Chemical Reactions and Enzymes Slide 7 of 34 Copyright Pearson Prentice Hall Enzymes Why are enzymes important to living things?

End Show 2–4 Chemical Reactions and Enzymes Slide 8 of 34 Copyright Pearson Prentice Hall Enzymes ●Some chemical reactions that make life possible are too slow or have activation energies that are too high to make them practical for living tissue. ●These chemical reactions are made possible by catalysts (biological catalysts are Enzymes). How: Lower Activation energy Result: Speed up rate of reaction

End Show 2–4 Chemical Reactions and Enzymes Slide 9 of 34 Copyright Pearson Prentice Hall An enzyme can decrease the energy of activation which speeds up the how fast the products are produced Figure 5.5A Reactants Products Enzyme EAEA

End Show 2–4 Chemical Reactions and Enzymes Slide 10 of 34 Copyright Pearson Prentice Hall Enzymes Lowering the activation energy has a dramatic effect on how quickly the reaction is completed.

End Show 2–4 Chemical Reactions and Enzymes Slide 11 of 34 Copyright Pearson Prentice Hall Enzymes Enzymes are very specific, generally catalyzing only one chemical reaction. For this reason, part of an enzyme’s name is usually derived from the reaction it catalyzes. Ex: Amylase breaks down amylose ( as type of starch found in flour) Amylose (starch) lots of glucose amylase

End Show 2–4 Chemical Reactions and Enzymes Slide 12 of 34 Copyright Pearson Prentice Hall Enzymes Ex: sucrase breaks down sucrose (table sugar) Substrate Products Enzyme

End Show 2–4 Chemical Reactions and Enzymes Slide 13 of 34 Copyright Pearson Prentice Hall Enzymes Exception: Catalase breaks down Hydrogen peroxide Oxygen gas – O 2 2 Hydrogen peroxide  2 water + oxygen + heat energy Catalase

End Show 2–4 Chemical Reactions and Enzymes Slide 14 of 34 Copyright Pearson Prentice Hall Enzyme Action ●For a chemical reaction to take place, the reactants must collide with enough energy so that existing bonds will be broken and new bonds will be formed. ●If reactants do not have enough energy, no reaction will take place. Reactants Products Activation Energy Barrier

End Show 2–4 Chemical Reactions and Enzymes Slide 15 of 34 Copyright Pearson Prentice Hall Enzyme Action The Enzyme-Substrate Complex Enzymes provide a site where reactants can be brought together to react, reducing the energy needed for reaction. The reactants of enzyme- catalyzed reactions are known as substrates.

End Show 2–4 Chemical Reactions and Enzymes Slide 16 of 34 Copyright Pearson Prentice Hall Enzyme Action The substrates glucose and ATP bind to the active site on the enzyme, hexokinase, forming an enzyme-substrate complex. The fit is so precise that the active site and substrates are often compared to a lock and key.

End Show 2–4 Chemical Reactions and Enzymes Slide 17 of 34 Copyright Pearson Prentice Hall Enzyme Action The enzyme and substrates remain bound together until the reaction is done and the substrates are converted to products. The products of the reaction are released and the enzyme is free to start the process again.

End Show 2–4 Chemical Reactions and Enzymes Slide 18 of 34 Copyright Pearson Prentice Hall Enzyme Action An Enzyme-Catalyzed Reaction

End Show 2–4 Chemical Reactions and Enzymes Slide 19 of 34 Copyright Pearson Prentice Hall Enzyme Action Regulation of Enzyme Activity Enzymes can be affected by any variable that influences a chemical reaction. ●Many enzymes are affected by changes in temperature. ●Enzymes work best at certain pH values. ●Enzymes work best at certain ionic (salt) concentrations pH Enzymatic Activity  pepsintrypsin

End Show 2–4 Chemical Reactions and Enzymes Slide 20 of 34 Copyright Pearson Prentice Hall Enzyme Action Regulation of Enzyme Activity Temperature is a measurement of the average amount of heat/ movement a group of molecules has –Too Cold: molecules move too slow  decrease reaction rate ●Ex: enzyme responsible for producing key tomato flavor molecule stops working below 55 deg. F –Too Hot: weak bonds between amino acids of the enzyme break  denatured enzyme!!!

End Show 2–4 Chemical Reactions and Enzymes Slide 21 of 34 Copyright Pearson Prentice Hall Enzyme Action Regulation of Enzyme Activity pH measures how acidic or basic the environment is Basic: pH greater than [Less H+] neutral: pH 7 (pure water and most cells) [H+ = OH-] Acidic:pH less than 7[more H+]

End Show 2–4 Chemical Reactions and Enzymes Slide 22 of 34 Copyright Pearson Prentice Hall Enzyme Action Regulation of Enzyme Activity Altered concentration of H+ interfere with amino acid chain folding of the enzyme (remember enzymes are proteins!) H+ H+ H+ H+ H+

End Show 2–4 Chemical Reactions and Enzymes Slide 23 of 34 Copyright Pearson Prentice Hall Enzyme Action Regulation of Enzyme Activity Enzymes work best at certain ionic (salt) concentrations Ex: Increased Na+ Cl- (table salt) Na+ Na+ Na+ Cl- Cl- Cl-

End Show 2–4 Chemical Reactions and Enzymes Slide 24 of 34 Copyright Pearson Prentice Hall Enzymes Cells can regulate the activities of enzymes. Most cells contain proteins that help to turn key enzymes “on” and “off” at critical stages in the life of the cell.

End Show 2–4 Chemical Reactions and Enzymes Slide 25 of 34 Copyright Pearson Prentice Hall Enzymes Enzymes play essential roles in: regulating chemical pathways. making material that cells need. Many antibiotics interfere with bacteria running necessary chemical pathways including stopping the enzymes that bacteria use to make their protective cell walls. releasing energy. Carbon monoxide poisoning stops cell’s enzymes from getting energy out of glucose transferring information. Pesticides stop enzymes that run insects nervous system