Metabolis lism is the totality of an organism s chemical reactions - PDF document

7/25/2016 Chemical Reactions of Life Metabolis lism is the totality of an organism’ s chemical reactions Metabolic lic Pathway: linked reactions where end product of one reaction becomes reactant of next reaction until final end product is created Chapter 8 - chem rxns divided into many small steps Metabo bolis lism Types of Metabolic Pathways Forms of Energy Energy: capacity to do work Catabolic lic pathways: Kine netic energy (KE): energy associated with motion • Breaking bonds to release energy (complex molecules  simpler molecules) • Hydrolysis reactions Thermal energy (heat): KE associated with random movement of atoms or • Exergonic molecules ex: digestive enzymes break down food  release energy Anabolic lic pathways Potent ntial energy (PE): stored energy as a result of its position or structure • Forming bonds by consuming energy (simple  complex molecules) • Chemical energy is PE available for release in a chemical reaction • Dehycration synthesis/ condensation reactions ex: glucose has PE in its bonds • Endergonic • Ex: formation of proteins from amino acids Energy can be converted from one form to another ex:. chemical  mechanical  electrical Conversion of Energy Forms Laws of Energy Transformation Thermodynamic amics: study of energy transformations that occur in nature • System: matter under study • Surroundin ing: everything else in the universe • Open system: energy and matter can be transferred between the system and its surroundings • Closed system: unable to exchange energy or matter with its surroundings (like liquid in a thermos) Orga ganis isms are open systems 1

7/25/2016 First Law of Thermodynamics Second Law of Thermodynamics The energy of the universe is constant Every energy transfer or transformation increases the entropy (disorder/randomness) of the universe. Energy can be transferred and transformed but • Energy is unusable or lost (converted to heat) during the transfers or energy cannot be created or destroyed transformations • Heat can be put to work if there if heat flows from warm  cooler areas ** also known as the law of Conservatio ion of Energy gy** • If temp is stable it can only be use warm body of matter (true of cells) As bear runs entropy is increased by release of heat and CO2 chemical reactions in brown bear will convert chemical (PE) in fish into KE of running Free Energy Spont ntane neous us Process: process that occurs without any input of energy “energetically favorable” Free energy : part of a system’s energy available to perform work (Gibbs free energy) when pressure and temperature are uniform throughout a system • Increases entropy of the universe (fast or slow process) ex: explosions  G = change in free energy = ability to do work rusting of a car  G =  H H - T  S • Living systems increase entropy of their surroundings ex: catabolic pathways break down food molecules  H = total energy in system animal release CO2 and H2O (depletion of T = absolute temperature in Kelvin (K = *C = 273) chemical energy)  S = change In system’s entropy result: heat generated during metabolism Used to predict whether process will be spont ntane neous (not require energy) **If entropy of a system is decreased, the entropy of the surroundings must increase Allows scient ntists to determine ne which reactions supply cellula ular energy for work Free Energy Stability  G G represents the difference between the free energy of the final stage and the free  G is only negative when process loses free energy from energy of the initial al stage initial to final stage • Measure of a system’s instability - its tendency to change to a more stable state (equilibrium) Higher energy  lower energy  G = G final stage - G initial al stage Final state of system has less free energy gy and is Less likely to change so therefore considered more stable 2

7/25/2016 Equilibrium Free Energy and Metabolism State of maxim imum stabilit lity Exergo gonic ic reactio ion “energy outward” Energy is released • no further net change in concentration of reactants & products Spontaneous reaction Decreases system’s free energy -  G • G is at lowest possible value in the system  G < 0 (negative) ex: ice to water The greater the decrease in free energy, the • System cannot do any work at equilibrium greater the amount of work that can be done • Process is spontaneous and can perform work only when it is Endergo gonic ic react ctio ion “energy inward” moving ng toward equilibrium Energy is required Absorbs free energy Metabolism is never at equilibrium um becaus use living ng cells are not in equilibrium um  G > 0 (cons nstant nt flow of material in and out of cells) +  G ex: steam to water Equilibrium and Work Energy Coupling in ATP Orga ganis isms need energy gy to live. A cell l does three main kinds of work: 1. mechanical (cilia beating, muscle contraction) 2 transport (pumping substances against gradient) 3. chemical (pushing of endergonic reactions) Cells do work by energy gy couplin pling exergo gonic ic react ctio ions (release energy) to drive endergo gonic ic react ctio ions (needing energy) Cellular respiration is similar to this system: Glucose is broken down in a series of exergonic reactions that power the work of the cell. Product of each reaction becomes reactant for the next so no reaction reaches equilibrium. Structure and Hydrolysis of ATP When the bonds between the phosphate groups are broken by hydrolysis  energy gy is rele leased ATP (adenosin ine tripho phospha phate) is the cell ’ s main energy source in energy coupling This release of energy comes from the chemical change to a state ATP = adenine + ribose + 3 phosphates of lower free energy, not in the phosphate bonds themselves When a terminal phosphate bond is broken a molecule of inorganic phosphate (HOPO3) P i leaves the ATP and becomes ADP ATP + H2O  ADP + Pi  G = 7.3 kcal/mol 3

7/25/2016 Regeneration of ATP Energy released during ATP hydrolysis performs the three types of cellular work. ATP Cycle le: shuttling of inorganic phosphate and energy • Phosphate group from ATP is transferred to another molecule • Coupled exergonic/ endergonic reactions Phospho phoryla lated intermedia iate: • Very quick process: muscle regenerates ATP in < 10 min. - molecule that accepts phosphate • Endergonic process: reversible process - more reactive/less stable than unphosphorylated • Uses free energy molecule Energy and Chemical Reactions Energy and Chemical Reactions Activ ivatio ion energy gy: (Ea): initial investment of energy to start a reaction (usually heat) Oxid idatio ion/ Reduct ctio ion Reactio ions (Redox): reactions in which Cataly lyst: substance that can change the rate of a reaction without electrons are transferred between atoms being altered in the process (lowers Ea needed to start rxn.) * reactions always come in pairs Enzyme: biological catalyst - Oxid idatio ion: reactant loses one or more electrons becomes positively charged - Reductio ion: reactant gains one or more electrons becomes negatively charged Enzymes Substrate Specificity Biological catalysts (end in “ase”) Substrate: reactant that binds to enzyme • Globular proteins Product ct: end result of reaction • Required for most biological reactions • Increase rate of reaction without being consumed Enzyme- substrate comple plex: temporary association • Reduce activation energy •Don’t change free energy (  G) released or required • Needed to maintain homeostasis • Mode of action: enzyme substrate comple plex • Highly specifiic- thousands of different enzymes in cells ex: protease- proteins lactase- lactose 4

7/25/2016 Induced Fit Model Factors that Affect Enzyme Activity • “Chemical handshake” Temperat ature 1. 3-D sturcture of enzyme fits substrate • Optim imal l tempe perature - humans (35- 40 C) 2. Substrate binds • greatest number of molecular collisions 3. Enzyme changes shape leading to a tighter fit • Decr crease tempe perature = decreased rate • Conformational change • molecules move slower • Brings chemical groups in position to catalyze • decreased collisions reaction • slows reaction rate • Can catalyze 1000’s of substrate/second • Incr crease above optimum tempe perature • Denatures enzyme = rate slows or stops “ Factors that Affect Enzyme Activity Effect of Temperature and pH pH pH • Optimal pH for most organisms(6-8) • pH too high or low (add or remove H+) • disrupts bonds, 3D shape (conformation) • Denatures enzyme Other Factors Affecting Activity Other Factors Affecting Activity Activat vator ors:: compounds that help enzymes Enzyme me concentrat ation • increase enzyme = higher rate until substrate used up Cofacto ctors Substrat ate concentrat ation • Non-protein inorganic compounds and ions (Mg, K, Ca, Zn, Fe) • • Found in enzyme molecule Increase substrate = higher rate until enzymes saturated Salinity (salt concentration) Coenzy zyme mes • No-protein organic molecules • High- disrupts bonds and 3D shape (Dead Sea) • Bind near enzyme active site • Denatures enzyme 5