Chapter 8 Metabolism Friday October 16 2015 8 05 AM Unifying Themes of Biology Life order growth reproduction responsiveness internal regulation All require energy Organisms open systems that take in and return energy to environment Energy Energy that which can or does move matter capacity for doing work o Potential energy stored energy stored in glucose o Kinetic energy energy associated with moving matter Energy can be converted from one form to the other Potential energy stored in the chemical bonds of gasoline and the car in motion is kinetic energy Why Do You Eat Biologically we eat for energy C6H12O6 glucose 6O2 6CO2 6H2O ENERGY Organisms need energy to drive cellular processes Thermodynamics study of energy transformations in a system o Organisms open systems Metabolism anabolism catabolism o 2 main groups opposite of each other Metabolic Pathway In cells compounds are built up and broken down in small steps by enzymes Each enzyme causes one step in a metabolic pathway to occur A starting molecule Enzyme 1 B Reaction 1 Enzyme 2 C Reaction 2 Enzyme 3 D product Reaction 3 Energy released The product of an earlier step serves as substrate of the next step Catabolic pathway energy released by breaking the bonds of larger molecules to form smaller molecules A starting molecule Enzyme 1 B Enzyme 2 C Enzyme 3 D product Reaction 1 Reaction 2 Reaction 3 Energy consumed Anabolic pathway energy consumed to build larger molecules from simpler molecules sometimes called biosynthetic pathways Coupled metabolism 2 pathways in energy coupling Catabolic pathway Energy released A B C Energy transferred Energy consumed Anabolic pathway C B A 1st Law of Thermodynamics Conservation of energy energy can be transferred transformed Amount of energy in universe is constant Energy can neither be created nor destroyed only converted from one form to another Energy used and released in any reaction must be balanced 2nd Law of Thermodynamics Energy affected matter in universe is becoming random Entropy disorder is increasing Energy is tending toward heat randomized energy 1st Law of Thermodynamics Cheetah eating chemical energy Energy transfer energy flows through the biosphere it is not created or destroyed in the biosphere o No energy created or destroyed Energy loss to entropy energy transfers in the biosphere are not 100 efficient most energy losses occur as heat Free Energy Energy available to do work in a system o Work is moving matter against an opposing force o Measure as the total amount of energy enthalpy the level of disorder entropy o deltaG exergonic reaction releases energy A spontaneous reaction o deltaG endergonic reaction take energy inside absorbs energy Not spontaneous The Free Energy Equation Enthalpy H is total energy in a system o deltaH exothermic reaction o deltaH endothermic reaction Entropy S is amount of disorder in a system T temperature Kelvin o deltaG deltaH T deltaS deltaG exergonic reaction deltaG endergonic reaction NO CALCULATION WILL BE DONE Spontaneous Reactions deltaG deltaH T deltaS o System must give up enthalpy total energy H must decrease o Give up order TS must increase o Or have both Enzymes Protein catalysts Can exhibit remarkable specificity Speed up reaction rates by lowering energy barrier Not used up in reactions needs a small amount Lower activation energy needed to start reaction initial barrier to all chemical reactions Energy Barrier Drop in initial energy barrier How does an enzyme lower the activation energy Enzyme Substrates o o o Enzyme substrate Complex Enzyme Products The enzyme physically binds to the substrate and though this binding strains the substrate s bonds and facilitates formation of the transition state The key is in the binding of between the enzyme and substrate The enzyme is not changing the enthalpy or entropy of the reaction thus does not change the deltaG Physical Binding The pocket groove or impression where the substrate binds is called the active site of the enzyme o Whole surface of enzyme should be hydrophilic interacting with water o Amino acid around the surface of the pocket is normally hydrophobic When the substrate binds to the active site the enzyme flexes in a way that closes the active site around the substrate like a glove o Higher temperature flex faster Catalytic Cycle of an Enzyme 1 Binding of substrate a Active site has complementary structure to substrate b Substrate binds to active site 2 Flexing of active site a Side chain start to work form ionic covalent bond with substrate 2 Straining of substrate bonds to form transition state 3 Release of products a Opens again for another round for catalyzation 2 Release open up Conditions that Affect Catalytic Potential of Enzymes 1 Substrate and enzyme concentrations a Rate of enzyme catalyzed reaction saturation curve b No substrate reaction rate is zero c As it increases reaction rate increases d Eventually the rate plateaus saturation curve all available enzyme in the system is saturated by the substrate e All available enzymes are occupied cannot catalyze anymore substrates 2 Temperature a Increase temperature increase reaction rate b Reaches optimal temperature quickly drops to zero i Denaturation of protein destroys the structure destroys the function 2 pH a Prefer neutral slightly basic pH of 7 5 b Highest activity reaction rate at this pH c Beyond pH will drop i Pepsin stomach protein digestive enzyme ii Trypsin small intestine 2 Cofactors a Positive co factor b Negative co factor i If needing co factor without co factor they are dead 2 Enzyme inhibitors a Negative inhibitor b Positive inhibitor i Inhibitor blocks the active site of enzyme ii Competitive inhibitor iii Non competitive inhibitor 1 Do not directly compete with the substrate 2 Cannot be reversed by simply increasing substrate concentration Q3 increase substrate concentration of the enzyme would overcome which of the following Allosteric inhibition cannot be reversed Competitive inhibition Denaturation of the enzyme once protein is deformed adding substrate does not help Saturation of the enzyme Insufficient cofactors Q4 The mechanism of end product inhibits an earlier step in the pathway is called Reversible inhibition Allosteric inhibition Feedback inhibition type of allosteric end product enzyme that catalyzes the first reaction Metabolic inhibition Pathway inhibition