Ground Rules of Metabolism Chapter 6

Free Radicals Unbound molecular fragments with the wrong number of electrons Unbound molecular fragments with the wrong number of electrons Highly reactive Highly reactive Can disrupt structure of molecules Can disrupt structure of molecules

Keeping Free Radicals in Check superoxide dismutasecatalase Figure 6.1 Page 96

Superoxide Dismutase Catalyzes the formation of hydrogen peroxide from oxygen-free radicals and hydrogen ions Catalyzes the formation of hydrogen peroxide from oxygen-free radicals and hydrogen ions Accumulation of hydrogen peroxide can be lethal to cells Accumulation of hydrogen peroxide can be lethal to cells

Catalase Catalyzes the formation of oxygen and water from hydrogen peroxide 2H 2 O > 2H 2 O + O 2

What Is Energy? Capacity to do work Capacity to do work Forms of energy Forms of energy Potential energy Potential energy Kinetic energy Kinetic energy Chemical energy Chemical energy

What Can Cells Do with Energy? Cells use energy for: Cells use energy for: Chemical work Chemical work Mechanical work Mechanical work Electrochemical work Electrochemical work

First Law of Thermodynamics The total amount of energy in the universe remains constant The total amount of energy in the universe remains constant Energy can undergo conversions from one form to another, but it cannot be created or destroyed Energy can undergo conversions from one form to another, but it cannot be created or destroyed

One-Way Flow of Energy The sun is life’s primary energy source The sun is life’s primary energy source Producers trap energy from the sun and convert it into chemical bond energy Producers trap energy from the sun and convert it into chemical bond energy All organisms use the energy stored in the bonds of organic compounds to do work All organisms use the energy stored in the bonds of organic compounds to do work

Second Law of Thermodynamics No energy conversion is ever 100 percent efficient No energy conversion is ever 100 percent efficient The total amount of energy is flowing from high-energy forms to forms lower in energy The total amount of energy is flowing from high-energy forms to forms lower in energy

Entropy Measure of degree of disorder in a system Measure of degree of disorder in a system

Energy Changes & Cellular Work Energy changes in cells tend to run spontaneously in the direction that results in a decrease in usable energy

Endergonic Reaction and 6H 2 O Energy in energy-poor starting substances 612 glucose - a product with more energy Figure 6.5a,b Page 100

Exergonic Reaction Energy out glucose - energy-rich starting substance products with less energy 66 Figure 6.5a,b Page 100

Structure of ATP three phosphate groups sugar (ribose) nucleotide base (adenine) Figure 6.6b Page 101

ATP: Main Energy Carrier ATP/ADP cycle regenerates ATP ATP/ADP cycle regenerates ATP energy input ADP + P i ATP energy output

Electron Transfers Oxidation - lose electron Oxidation - lose electron Reduction - gain electron Reduction - gain electron Central to the formation of ATP during photosynthesis and aerobic respiration Central to the formation of ATP during photosynthesis and aerobic respiration

Participants in Metabolic Pathways Energy Carriers Enzymes Cofactors Reactants Reactants Intermediates Intermediates Products Products

Degradative and Anabolic Pathways ATP BIOSYNTHETIC PATHWAYS (ANABOLIC) ENERGY INPUT DEGRADATIVE PATHWAYS (CATABOLIC) energy-poor products large energy-rich molecules simple organic compounds ADP + P i

Types of Reaction Sequences BRANCHING PATHWAY LINEAR PATHWAY CYCLIC PATHWAY ABCDE F KJI G NML H Figure 6.8 Page 102

Which Way Will a Reaction Run? Nearly all chemical reactions are reversible Nearly all chemical reactions are reversible

Chemical Equilibrium HIGHLY SPONTANEOUS EQUILIBRIUM HIGHLY SPONTANEOUS RELATIVE CONCENTRATION OF PRODUCT RELATIVE CONCENTRATION OF REACTANT Figure 6.9 Page 103

Chemical Equilibrium Energy in the reactants equals that in the products Energy in the reactants equals that in the products Product and reactant molecules usually differ in energy content Product and reactant molecules usually differ in energy content Therefore, at equilibrium, the amount of reactant almost never equals the amount of product Therefore, at equilibrium, the amount of reactant almost never equals the amount of product

No Vanishing Atoms Law of conservation of mass Law of conservation of mass Reactions rearrange atoms, but they never destroy them Reactions rearrange atoms, but they never destroy them As many atoms of each element in all the products as there were in all the reactants As many atoms of each element in all the products as there were in all the reactants

Electron Transfer Chains Arrangement of enzymes, coenzymes, at cell membrane Arrangement of enzymes, coenzymes, at cell membrane Works like a bucket brigade in fighting fires in that electrons are transferred from a carrier to the next in the cell membrane. Works like a bucket brigade in fighting fires in that electrons are transferred from a carrier to the next in the cell membrane.

Enzyme Structure and Function Enzymes are catalytic molecules They speed the rate at which reactions approach equilibrium

Four Features of Enzymes 1) Enzymes do not make anything happen that could not happen on its own. They just make it happen much faster. 2) Reactions do not alter or use up enzyme molecules.

Four Features of Enzymes 3) The same enzyme usually works for both the forward and reverse reactions. 4) Each type of enzyme recognizes and binds to only certain substrates.

Activation Energy For a reaction to occur, an energy barrier must be surmounted For a reaction to occur, an energy barrier must be surmounted Enzymes make the energy barrier smaller Enzymes make the energy barrier smaller activation energy without enzyme activation energy with enzyme energy released by the reaction products starting substance Figure 6.12a Page 105

Factors Influencing Enzyme Activity Coenzymes and cofactors regulatorsTemperaturepH Salt concentration

Effect of Temperature Small increase in temperature increases molecular collisions, reaction rates Small increase in temperature increases molecular collisions, reaction rates High temperatures disrupt bonds and destroy the shape of active site High temperatures disrupt bonds and destroy the shape of active site Figure 6.17b Page 109

Effect of pH Figure 6.17c Page 109

Beer, Enzymes, and Your Liver Alcohol dehydrogenase Alcohol dehydrogenase Acetaldehyde dehydrogenase Acetaldehyde dehydrogenase Cytochrome and catalase Cytochrome and catalase Heavy drinking destroys liver cells and body’s ability to detoxify alcohol Heavy drinking destroys liver cells and body’s ability to detoxify alcohol