Ground Rules of Metabolism Chapter 6 Free Radicals

Ground Rules of Metabolism Chapter 6

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

Keeping Free Radicals in Check superoxide dismutase catalase Figure 6. 1 Page 96

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

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

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

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

First Law of Thermodynamics n n 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

One-Way Flow of Energy n n n The sun is life’s primary energy source 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

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

Entropy n 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 glucose - a product with more energy + 602 and 6 H 2 O Energy in energy-poor starting substances 6 12 Figure 6. 5 a, b Page 100

Exergonic Reaction glucose energy-rich starting substance + 602 Energy out 6 6 products with less energy Figure 6. 5 a, b Page 100

Structure of ATP nucleotide base (adenine) three phosphate groups sugar (ribose) Figure 6. 6 b Page 101

ATP: Main Energy Carrier n ATP/ADP cycle regenerates ATP energy input energy output ADP + Pi

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

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

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

Types of Reaction Sequences A B C D E F LINEAR PATHWAY K CYCLIC PATHWAY J G I BRANCHING PATHWAY N M L H Figure 6. 8 Page 102

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

Chemical Equilibrium RELATIVE CONCENTRATION OF REACTANT RELATIVE CONCENTRATION OF PRODUCT HIGHLY SPONTANEOUS EQUILIBRIUM HIGHLY SPONTANEOUS Figure 6. 9 Page 103

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

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

Electron Transfer Chains n Arrangement of enzymes, coenzymes, at n 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 n n For a reaction to occur, an energy barrier must be surmounted Enzymes make the energy barrier smaller Figure 6. 12 a Page 105 starting substance activation energy without enzyme activation energy with enzyme energy released by the reaction products

Factors Influencing Enzyme Activity Coenzymes and cofactors regulators Temperature p. H Salt concentration

Effect of Temperature n n Small increase in temperature increases molecular collisions, reaction rates High temperatures disrupt bonds and destroy the shape of active site Figure 6. 17 b Page 109

Effect of p. H Figure 6. 17 c Page 109

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