Metabolism: the sum total of an organism’s chemical reactionsCatabolic (pathways involved in degradation): Release energy by breaking down complex molecules to simpler compoundsAnabolic (pathways involved in synthesis): Consume energy to build complicated molecules from simpler ones. Sometimes called biosynthetic pathwaysOrganisms transform and transfer energyEnergy: capacity to do workPotential Energy: energy that an object possesses because of its structure or position (usually chemical bond energy in biological systems)Kinetic Energy: relative motion of objectsEnergy transfers by organisms are subject to two laws of thermodynamics1st Law of Thermodynamics (principle of conservation of energy): energy can be transferred and transformed, but it cannot be destroyed; the energy of the universe is constant2nd Law of Thermodynamics: every energy transfer or transformation makes the universe more disordered (every process increases entropy). With every transfer of energy, some usable energy is lost as “heat”Entropy (S): quantitative measure of disorder or randomnessFree energy and spontaneous reactionsFree Energy (G): is the portion of energy available to do workdeltaG = deltaH – TdeltaSDifference between the total energy (deltaH, or enthalpy) and the energy not available to do work (TdeltaS), where T is the absolute temperature and S is entropyIn a chemical reaction the energy change (deltaG) between the reactants and the products is the amount of useable energy that can be harvested to do work.deltaG = G(products) – G(reactants)deltaG negative: energy released and the forward reaction will occur spontaneouslydeltaG positive: energy required and the forward reaction will not occur spontaneouslyAs a chemical reaction approaches equilibrium the free energy (deltaG) of the system decreasesWhen a reaction is pushed away from equilibrium, the free energy (deltaG) of the system increasesAt chemical equilibrium, deltaG = 0When deltaG = 0, no work can be doneTypes of Chemical Reactions (based on free energy changes)Exergonic (Fig 8.6): release energy when they occurEX. Hydrolysis of ATP (Fig 8.9): “High-energy molecule”These phosphate bonds aren’t really high energy as they are often referred toThe reason tat ATP is a high-energy molecule is that the products (ADP + P) have substantially lower free energy than the reactantsThis means that the energy difference between the products and reactants is enormous, which will provide a lot of energy to do workThe structure of the ATP molecule is what makes it such an efficient energy source (form dictates function)The 3 phosphate groups all located next to each other have negative charges (like charges repel)The phosphate tail is like a compressed spring: When one of these bonds is broken, a huge amount of energy is releasedEndergonic (Fig 8.6): require input of energy to occurHow does ATP drive work?If the change in free energy deltaG for an endergonic reaction is less than the amount of energy releases by ATP hydrolysis, then the 2 reactions can be coupled so that, overall, the reactions are exergonicCoupled reactions: energy released from exergonic reactions (ATP hydrolysis) is used to power endergonic reactions (protein synthesis)Catalysts and EnzymesCatalysts: substances that speed up the rates of exergonic chemical reactions but are not themselves used up or alteredEnzymes: biological catalystsMost are proteinsHighly specific for the chemicals they act onEA = activation energy (Fig 8.14 and 8.15): lowers the activation energyDoesn’t alter the change in free energy between products and reactantsSubstrate-specific: a substrate is a molecule that reacts with the help of the enzymeActive Site: area of enzyme that specifically binds and reacts with the substrateA cell’s chemical and physical environment affects enzyme activityTemperatureCofactors (electron carriers that assist enzymes, co-enzymes: vitamins)Enzyme inhibitors: molecules that can interact with an enzyme and make it inactiveEnzyme InhibitorsCompetitive inhibitors: reduce enzymatic activity by blocking the active site. Preventing substrates from entering the active sites. Often resemble the substrate and compete for access to the active site. Called mimics.Allosteric inhibitors: do not directly compete with the substrate for access to the active site. Bind a different part of the enzyme and causes a conformational change in the enzyme that affects the active site.Cellular Respiration: harvesting chemical energy, catabolic pathways yield energy by oxidizing organic fuels.Cellular Respiration and Fermentation are catabolic pathwaysFermentation: is the partial degradation of sugars that occurs without the use of oxygen. An anaerobic process.Cellular Respiration: an ATP-producing pathway in which the ultimate electron acceptor is oxygen. An aerobic process. (can live maybe 3 or 4 minutes w/o ATP or oxygen)C6H12O6 + 6O2 6CO2 + 6H2O + Energy (ATP and heat)deltaG = -686 kcal/mol of sugarRespiration is the removal of energy from organic molecules and storing it in ATPRedox reactions (aka Oxidation-reduction reactions) are exergonic reactions which involve a transfer of electrons from a less electronegative atom to a more electronegative atomAn atom that receives an electron gets reduced (receives a negative so the amount of positive charge gets reduced): Oxidizing AgentAn atom that loses an electron gets oxidized: Reducing AgentExergonic reaction, potential energy gets releasedNa + Cl Na+ + Cl-Na becomes oxidized, lost an electron (Reducing Agent)Cl got reduced, gains an electron (Oxidizing Agent)So: Xe- + Y X + Ye-X is oxidized (Reducing Agent)Y is reduced (Oxidizing Agent)Oxidizing and reductions always go together. A molecule can’t be oxidized without another molecule being reduced.Doesn't have to be a complete transfer if electrons from one atom to another, it can involve a change in the level of electron sharing within a covalent bondIn methane, (CH4), C and H have similar EN’s (nonpolar covalent bond): so the valence electrons are shared equallyWhen methane reacts with oxygen, carbon dioxide is formedCarbon is now bonded to oxygen, which is more electronegative than hydrogen. So carbon has partially lost its shared electrons and has become oxidized. Oxygen becomes reduced. (Fig 9.3)ElectronegativityPulling an electron away from an atom requires energy. The more EN an atom is, the more energy is required to take an electron from itAn electron loses
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