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Lecture 4

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Biology 1002B
Tom Haffie

Lecture 4: Energy & Enzymes  2 law – disorder of system & surroundings increases  Entropy must occur  System & surroundings; there is not much order, whereas a cell such as clamydomonas has a lot of order  Proteins are ordered nd  Order = low entropy; but how does it go against the 2 law  Cells are an open system; there is a free exchange of energy and matter between the system of the cell and surroundings which enables it to bring in huge amounts of energy which is what it uses to maintain order  If you stop bringing energy into the cell, it falls apart and disorder takes over  As a consequence, cells spew out a lot of heat which increases the disorder of the surroundings Free Energy  Energy available to do work = free energy  ΔG = ΔH - TΔS A ------>B  ΔG = Free Energy  ΔH = Enthalpy  TΔS = Entropy  Enthalpy can be endothermic (+) or exothermic (-)  Free Energy can be endergonic (+) or exergonic (-)  For Entropy, there can be more disorder (+) or less disorder (-)  Will the reaction proceed as written or not?  Reactions tend to be spontaneous when (-ΔG) when… the reaction is exothermic and there is more potential energy in A than B  Glucose has a lot of energy in it, it will spontaneously break down to C2  It also tends to be spontaneous when the products are more disordered than the reactants and entropy goes up Contributions of enthalpy and entropy  Fermentation of glucose to ethanol: C 6 12(6)  2 C H5OH5l) + CO (g2  Whenever you go to a phase change from solid, to liquid or gas, it creates more disorder  The reaction is exothermic  When ΔH goes down and TΔS goes down; it contributes to having a large ΔG  Melting of ice H2O (s) -> 2 O (l)  ΔH increases, ΔG decreases  What drives this is the massive change in disorder TΔS is huge  All entropy driven Enzymes  Enzymes have the ability to increase the rate of the reaction  Huge effect on the rate of a spontaneous reaction  10 – 10 times faster  Why does life need enzymes  If it wasn’t for enzymes to carry out the reactions, the temperatures you would need to make the reaction go would be much higher  High temperature is incongruent with life  Cells/biological molecules can’t deal with high temperatures, so the huge evolutionary advantage of the evolution of enzymes was to get reactions to go fast without raising temperatures and pressures  What enzymes do and don’t do  A ---> B ---> C  First reaction: it is spontaneous; ΔG is negative; enzymes can increase the rate of this reaction  Second reaction: ΔG is positive and is not spontaneous, so enzymes cannot do anything; it will not make the reaction proceed; it needs energy to proceed and enzymes do not provide energy for a reaction  You need energy, and energy usually comes from ATP  There is often an enzyme to help the reaction to go, but it doesn’t provide the energy  Enzyme brings the ATP and the substrate together, but can’t do anything by itself Exergonic Reaction Energy Profile  Negative ΔG  What prevents the reaction from going quickly is the reactants need to acquire the transition state  EArepresents a barrier  The energy to get to the transition state is known as the activation energy  They need to acquire a certain amount of energy to go to the transition state  Propane is a good example:  Thermodynamically unstable – but… it is thermodynamically unstable (-ΔG)  There is a lot of potential energy; however, kinetically it is very stable  There is a lot of free energy  Lighting a ma
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