Test 3 October 30th Chapter 8 An introduction to Metabolism Metabolism the sum total of an organism s chemical reactions 2 types 1 Catabolic pathways involved in degradation Release energy by breaking down complex molecules to simpler compounds steroids 2 Anabolic pathways involved in synthesis Consume energy to build complicated molecules from simpler ones Sometimes called biosynthetic pathways Organisms transform and transfer energy Energy is the capacity to do work Potential energy is that an object possesses because of its structure or position Usually chemical bond energy in biological systems Ex Ball at the top of the hill has a lot of potential energy Kinetic energy is the relation motion of objects Energy transfers by organisms are subject to two laws of thermodynamics First Law of Thermodynamics energy can be transferred and transformed but it cannot be destroyed ex the energy of the universe is constant Known as the principle of conservation of energy Second Law of Thermodynamics states that every energy transfer or transformation makes the universe more disordered ex every process increases entropy In other words with every transfer of energy some usable energy is lost as heat Entropy S is the quantitative measure of disorder or randomness always increases Free energy and spontaneous reactions Free energy G is the proton of energy available to do work It s the difference between the total energy H or enthalpy and the energy not available to do work T S where T is the absolute temperature and S is entropy In a chemical reaction the energy change G between the reactants and the products is the amount of useable energy that can be harvested to do work G H T S G H T S G G final products G starting material reactants If G is negative the reactants are higher energy released exergonic If G is positive the products are higher energy required endergonic As a chemical reaction approaches equilibrium the free energy G of the When a reaction is pushed away from equilibrium the free G of the If A B C D Reactants Products system decreases system increases At chemical equilibrium G 0 When G 0 work can be done G If G is negative the forward reaction will occur spontaneously and the energy will be released If G is positive the forward reaction will not occur spontaneously energy will have to be added to the system in order for the forward reaction to occur Types of Chemical Reactions Based on their free energy changes Exergonic release energy when they occur products have less free energy than the reactants reaction is energetically downhill spontaneous reaction G is negative Endergonic require input of energy to occur products have more free energy than reactants reaction is energetically uphill nonspontaneous reaction requires an energy source G is positive Figure 8 9 3 phosphate have negative charges of oxygen they repel so when water gets added it attacks the bond on the end causing energy to happen High energy molecule These phosphates bonds aren t really high energy as they are often referred to The reason that ATP is a high energy molecule is that products ADP P have a substantially lower free energy than the reactants This means that the energy difference between the products and reactants is enormous which will provide a lot of energy to do work Phosphate tail The 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 released How does ATP drive work If the change in free energy G for an endergonic reaction is less than the amount of energy released by ATP hydrolysis then the 2 reactions can be coupled so that overall the reactions are exergonic Coupled reactions energy released from exergonic reactions ATP hydrolysis is used to power endergonic reactions protein synthesis Catalysts Enzymes Catalysts are substances that speed up the rates of exergonic chemical reactions but are not themselves used up or altered Enzymes are biological catalysts LOWER ACTIVATION ENERGY Most are proteins They are highly specific for the chemicals they act on Figure 8 14 E activation energy G change in free energy An enzyme Lowers the activation energy of a reaction Does NOT alter the change in free energy between reactants and products Enzymes are substrate specific Substrate a molecule that reacts with the help of the enzyme Active site area of enzyme that specifically binds and reacts with the substrate Like different keys for different locks A cell s chemical and physical environment affects enzyme activity 1 Temperature and pH 2 Cofactors assists enzymes 3 Enzyme inhibitors molecules that can interact with an enzymes and turn it off Enzyme Inhibitors Competitive inhibitors reduce enzymatic activity by blocking 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 noncompetitive inhibitor Do not directly compete with the substrate for success to the active site Bind to a different part of the enzyme and causes a conformational change in the enzyme that affects the active site Chapter 9 Cellular Respiration Harvesting Chemical Energy Catabolic pathways yield energy by oxidizing organic fuels Cellular respiration and fermentation are catabolic pathways Fermentation is the partial degradation of sugars that occurs without the use of oxygen An anaerobic process Cellular respiration is an ATP producing pathway in which the ultimate electron acceptor is oxygen Aerobic process Without ATP you would die Redox reactions aka Oxidation reduction reactions are exergonic reactions which involve the transfer of electrons from a less electronegative atom to a more electronegative atom Electrons are NEGATIVE An atom that receives an electron gets reduced Oxidizing agent Cl An atom that loses an electron gets oxidized Reducing agent Na Redox Reactions Oxidation is the loss of electrons from one atom Reduction is the gain or addition of electrons to an atom Called this because it reduces the amount of positive charge in that atom There s a big magnet and a small magnet There is a piece of metal hydrogen electron in the middle The atom would go to the big magnet Movement to a more electronegative atom is exergonic From this reaction gets potential
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