Chapter 8 - MetabolismFriday, October 16, 20158:05 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)oPotential energy - stored energy, stored in glucoseoKinetic 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 systemoOrganisms - open systems-Metabolism = anabolism + catabolismo2 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 Enzyme 2 C Enzyme 3 D (product) Reaction 1 Reaction 2 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 Energy transferred Energy consumed Anabolic pathwayA ---> B ---> C --------------------> ----------------------> 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 balanced2nd 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 biosphereoNo 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 systemoWork is moving matter against an opposing forceoMeasure as the total amount of energy (enthalpy) - the level of disorder (entropy)o-deltaG = exergonic reaction (releases energy)-A spontaneous reactiono+deltaG = endergonic reaction (take energy inside, absorbs energy)-Not spontaneous The Free Energy Equation-Enthalpy (H) is total energy in a systemo-deltaH = exothermic reactiono+deltaH = endothermic reaction-Entropy (S) is amount of disorder in a system-T = temperature (Kelvin)odeltaG = deltaH - T*deltaS--deltaG = exergonic reaction-+deltaG = endergonic reaction-NO CALCULATION WILL BE DONE Spontaneous Reactions--deltaG = deltaH - T*deltaSoSystem must give up enthalpy, total energy (H must decrease)oGive up order (TS must increase)oOr 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---------><---------Enzyme-substrateComplex---------><---------Enzyme +ProductsoThe enzyme physically binds to the substrate and though this binding, strains the substrate's bonds and facilitates formation of the transition stateoThe key is in the binding of between the enzyme and substrateoThe 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 enzymeoWhole surface of enzyme should be hydrophilic - interacting with wateroAmino 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"oHigher temperature - flex faster Catalytic Cycle of an Enzyme1. Binding of substratea. Active site has complementary structure to substrateb. Substrate binds to active site2. Flexing of active sitea. Side chain start to work, form ionic/covalent bond with substrate2. Straining of substrate bonds to form transition state3. Release of productsa. Opens again for another round for catalyzation 2. Release/open up Conditions that Affect Catalytic Potential of Enzymes1. Substrate and enzyme concentrationsa. Rate of enzyme-catalyzed reaction (saturation curve)b. No substrate = reaction rate is zeroc. As it increases, reaction rate increasesd. Eventually the rate plateaus = saturation curve - all available enzyme in the system is saturated by the substratee. All available enzymes are occupied, cannot catalyze anymore substrates2. Temperaturea. Increase temperature = increase reaction rateb. Reaches optimal temperature, quickly drops to zeroi. Denaturation of protein - destroys the structure, destroys the function2. pHa. Prefer neutral, slightly basic pH of 7.5b. Highest activity, reaction rate at this pHc. Beyond pH will dropi. Pepsin (stomach protein digestive enzyme)ii. Trypsin (small intestine)2. Cofactorsa. Positive co-factorb. Negative co-factori. If needing co-factor, without co-factor they are dead2. Enzyme inhibitorsa. Negative inhibitorb. Positive inhibitori. Inhibitor blocks the active site of enzymeii. Competitive inhibitoriii. Non-competitive inhibitor1. Do not directly compete with the substrate2. 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 cofactorsQ4. The mechanism of end product inhibits an earlier step in the pathway is called-Reversible inhibition-Allosteric