Principles of Bioenergetics: Gibbs Free Energy Introduction

Principles of Bioenergetics Gibbs Free Energy Introduction: Gibbs Free Energy basically tells you whether or not a reaction will occur Units are reported as J/mol Gibbs free energy has nothing to do with the pathway, just the difference in overall free energy between the products and the reactants (state function) Gibbs free energy is something that can be calculated but NOT measured (using the equation: 𝛥𝐺 = 𝛥𝐻 − 𝑇𝛥𝑆 → You CAN measure the change in enthalpy, entropy, and temperature of a reaction) An Analogy for Gibbs Free Energy: Naturally, a 𝛥𝐻 < 0 and 𝛥𝑆 > 0 make sense because if this is true, then the reaction will proceed spontaneously With regards to 𝛥𝐺 a lot of the time it depends on the T value (if it is large enough to overcome the 𝛥𝐻) Heat Transfer: The difference between heat and temperature: Heat is the amount of energy that is transferred due to a change in temperature Temperature is the average kinetic energy of the molecules of what we are measuring Heat should always be referred to as heat transferred and occurs between a system and its surroundings Heat transfer is denoted with the lowercase letter q Energy lost by the system is transferred into the surroundings (-q) and vice versa (+q) 𝑞!"!#$% = −𝑞!&''(&)*+),! Enthalpy: Enthalpy is basically just a fancy term describing the heat transfer of a given reaction and is always described as a change (𝛥𝐻) and is in units of J/mol Endothermic reactions occur when 𝛥𝐻 > 0 and Exothermic reactions occur when 𝛥𝐻 < 0 We cool down by allowing our body’s energy to be dissipated into the sweat, causing it to evaporate (endothermic with regards to the water/sweat) We shiver because ATP hydrolysis is an exothermic reaction, meaning that it gives off energy allowing us to warm up (exothermic) Exothermic reactions produce heat as a product Endothermic reactions have heat as a reactant Le Chatelier's Principle: A+B→C+D If you increase [A], then you decrease [B] and increase concentration of [C] and [D] since there are now more A molecules allowing for the correct collision with B, further pushing toward product formation You can use equilibrium constant equation in order to figure out the new concentrations when you add in a specific amount of reactant/product Thermodynamics vs. Kinetics: Kinetics has to do with the activation energy (the energy required in order to form a high energy transition state) barrier that must be crossed in order for the reaction to proceed while thermodynamics simply has to do with the overall change in free energy Enzymes affect the kinetics of the reaction and NOT the thermodynamics of it Although you can be thermodynamically favorable, it takes so much activation energy even to start the reaction that it won’t proceed kinetically Extra Notes: ATP is cleaved via its phosphoanhydride group and goes alpha, beta, and gamma (going from inside to outside) Standard Reduction Potential is a measure of the tendency of a chemical species to be reduced (higher the value, the more likely it is to gain electrons) Standard Oxidation Potential is a measure of the tendency of chemical species to be reduced (higher the value, the more likely it is to lose electrons) Cleavage of bonds requires the input of energy Glucose and oxygen both have higher levels of free energy than their products CO2 and H2O because we want to harness its energy for use later Allosteric Activators bind to locations on an enzyme away from the active site, inducing a conformational change that increases the affinity of the enzyme's active site(s) for its substrate(s)