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enzyme and energy
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Chapter 4
Enzymes and Energy
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Enzymes
Biological catalysts. Increase rate of chemical reactions. Most enzymes are proteins with
diverse structure.
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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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Activation Energy
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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.
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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.
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Control of Enzyme Activity
Rate of enzyme-catalyzed reactions measured by the rate substrates are converted to products.
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Control of Enzyme Activity
Factors influencing rate: Temperature pH [cofactors and coenzyme] [enzyme and substrate] Stimulatory and inhibitory effects of
products
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Effect of Temperature
Increase in temperature increases rate of reaction.
At body temperature, plateaus.
Denature at high temperatures.
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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.
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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 H20 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.
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Reversible Reactions
H20 + C02 H2C03
Direction of reversible reaction depends on the concentration of molecules to the left and right of the arrows.
ca
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Sequence of enzymatic reactions that begins with initial substrate, progresses through intermediates and end with a final product.
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An intermediate can serve as substrate for 2 different enzymes, producing 2 different products.
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Negative feedback inhibition. One of the finalproducts inhibits the activity of the branch enzyme.Prevents final product accumulation.
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Inborn Errors of Metabolism
Inherited defect in a gene. Quantity of intermediates formed
prior to the defect increases. Final product decreases, producing
a deficiency.
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Cannot produce tyrosine, PKU results.Cannot produce melanin, albinism results.
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Bioenergetics
Flow of energy in living systems. 1st law of thermodynamics:
Energy can be transformed, but it cannot be created or destroyed.
2nd law of thermodynamics: Energy transformations increase entropy. Free energy can be used to do work.
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Endergonic Reactions
Chemical reactions that require an input of energy.
Products must contain more free energy than reactants.
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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 H20 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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Universal energy carrier of the cell.
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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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Reduced form.
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Oxidized form.
