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Lecture 4

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Biology 1001A
Tom Haffie

Meaning of potential, kinetic, chemical energy, closed, open vs. isolated systems, First Law of Thermodynamics, Second Law of Thermodynamics, entropy, spontaneous reaction, enthalpy (H), DH, exothermic, endothermic, Gibbs Free Energy, exergonic, endergonic, DG, catalyst, rate of reaction, energy of activation (EA), transition state, kinetic stability, active site, catalytic cycle - Why life does not go against the second law - ● Cells are in open systems, allows for free exchange of energy with surroundings, this maintains order and low entropy ○ releases heat and this increases disorder of surroundings ● Without the energy, disorder would take over and cell would die ● Life does not go against second law as while there is low entropy within the system, as a result of taking in energy, disorder of surroundings is increasing Why life needs to consume energy - ● Life needs to consume energy to maintain order and survive ● If energy is not being consumed, disorder takes over within the system and life will end Components of Gibbs Free Energy equation - ● Free energy is the energy available for use ● ΔG =ΔH - TΔS ● ΔG: Free Energy ○ If positive, endergonic ○ If negative, exergonic ● ΔH: Enthalpy ○ If positive, endothermic ○ If negative, exothermic ● ΔS: Entropy ○ If positive, more disorder ○ If negative, less disorder Whether or not a given reaction will be spontaneous, givenΔG - ● Spontaneous reactions will proceed as written, do not need external energy ● Areaction tends be spontaneous ifΔG is negative aka exergonic ○ ΔH is exothermic; products have less potential energy than reactants (eg. combustion) ○ ΔS will be more disordered; entropy higher in products than reactants (positive ΔS) Role of enzymes in endergonic vs. exergonic reactions - ● Spontaneity of reaction is not related to rate of re12tion20 ● Enzymes increase rate of a spontaneous reaction from 10 to 10 (ΔG is negative/exergonic) ● However, if a reaction is endergonic, an enzyme cannot act on it as the reaction needs energy to proceed but enzymes don’t provide energy! You needATP and an enzyme to speed it up Relationship between activation energy and rate of reaction - ● By lowering the activation energy, many more molecules can reach the transition state and the reaction can proceed ● Because mor
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