Chapter 4 Enzymes and Energy

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Enzymes Biological catalysts. Increase rate of chemical reactions. Most enzymes are proteins with diverse structure.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Biological Catalyst Chemical that: Increases the rate of a reaction. Is not changed at the end of the reaction. Does not change the nature of the reaction or final result. Lowers the activation energy required. Activation energy: Amount of energy required for a reaction to proceed.

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mechanism of Enzyme Action Each type of enzyme has has a characteristic 3-dimensional shape (conformation). Has ridges, grooves, pockets lined with specific amino acids. Pockets active in catalyzing a reaction are called the active sites of the enzyme.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mechanism of Enzyme Action Lock-and-key model of enzyme activity: Reactant molecules (substrates) have specific shapes to fit into the active sites. Substrate fits into active sites in enzyme. Enzyme-substrate complex dissociates. Products of reaction formed and free enzyme.

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Naming of Enzymes Enzyme name ends with ase. Classes of enzymes named according to activity. Enzymes that have the same activity in different organs may make different models called isoenzymes.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Control of Enzyme Activity Rate of enzyme-catalyzed reactions measured by the rate substrates are converted to products.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Control of Enzyme Activity Factors influencing rate: Temperature pH [cofactors and coenzyme] [enzyme and substrate] Stimulatory and inhibitory effects of products

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Effect of Temperature Increase in temperature increases rate of reaction. At body temperature, plateaus. Denature at high temperatures.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. pH Each enzyme exhibits peak activity at narrow pH range (pH optimum). Optimum pH reflects the pH of the body fluid in which the enzyme is found.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cofactors and Coenzymes Cofactor: Attachment of cofactor causes a conformational change in enzyme. Participate in temporary bonds between enzyme and substrate. Coenzymes: Cofactors that are organic molecules derived from niacin, riboflavin and other H 2 0 soluble vitamins.

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Substrate Concentration Rate of product formation will increase as the [substrate]. Plateau of maximum velocity occurs when enzyme is saturated.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Reversible Reactions H C0 2 H 2 C0 3 Direction of reversible reaction depends on the concentration of molecules to the left and right of the arrows. ca

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sequence of enzymatic reactions that begins with initial substrate, progresses through intermediates and end with a final product.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. An intermediate can serve as substrate for 2 different enzymes, producing 2 different products.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Negative feedback inhibition. One of the final products inhibits the activity of the branch enzyme. Prevents final product accumulation.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Inborn Errors of Metabolism Inherited defect in a gene. Quantity of intermediates formed prior to the defect increases. Final product decreases, producing a deficiency.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cannot produce tyrosine, PKU results. Cannot produce melanin, albinism results.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Bioenergetics Flow of energy in living systems. 1 st law of thermodynamics: Energy can be transformed, but it cannot be created or destroyed. 2 nd law of thermodynamics: Energy transformations increase entropy. Free energy can be used to do work.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Endergonic Reactions Chemical reactions that require an input of energy. Products must contain more free energy than reactants.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Exergonic Reactions Convert molecules with more free energy to molecules with less. Release energy in the form of heat. Heat is measured in calories. Calorie: Amount of heat to raise the temperature of one cubic centimeter of H 2 0 one degree Celsius.

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Coupled Reactions: ATP Cells cannot use heat for energy. Require energy released in exergonic reactions (ATP) to be directly transferred to chemical- bond energy in the products of endergonic reactions.

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Oxidation-Reduction Reduced: Molecule/atom gains electrons. Reducing agent: Molecule/atom that donates electrons. Oxidized: Molecule/atom loses electrons. Oxidizing agent: Molecule/atom that accepts electrons. May involve the transfer of H + rather than free electrons.

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Oxidized form.