Main Ideas!- The chemical and physical properties of watere make it useful as solvent, conductor, acid or base, pH regulator.!- Common ionizationns involve: carboyxl-, amino-, sulfhydryl-, and hydroxyl-groups plus the N in imidazole!- The equilibrium constant of a rxn tells you which direction is favored, but not how fast it will get there.!- The change in free energy can be calculated from the Keq value; it is diff. between standard state and real life scenario. Learning Objectives 1) Know the main characteristics of water 2) Understand the relationship between equilibrium and free energy 3) Understand the difference between free energy of a rxn and standard free energy 4) Be able to solve simple problems determining the delta G of a coupled rxn from its component rxns 1) Know the main characteristics of water - Most abundant biomolecule in our body!- Chemical dipole: H + charge, O - charge --> the polarity of water makes it a good solvent!!- Hydrogen bonding= Intermolecular bonding due to attraction between H (partial +) and O (partial -)!- molecules that H bond w/bond dissolve well in water!- H bonds aren't very strong (1 kcal/mole), but you have many many H bonds it can add up to be a considerable factor in attraction!- Water is not all H20--it ionizes into hydronium (H30+) and hydroxyl ions (OH-). !- Because of this, is can act as an acid (donor of H+) or a base (acceptor of H+). This is a very small part in a water solution.!- Common ionizations: often involve carboxyl and amine functions!- Other imp.= sulfhydryls, N aton of imidazole, hydroxyl groups of serin, threonine, and tyrosine!- Depends on the pK value as to whether this ionization happens or not 2) Understand the relationship between equilibrium and free energy - Keq= where the forward and reverse rxns occur at the same rate= the number of A and B molecules being convered to C and D molecs = the # of C and D molecs being converted to A and B molecs!- if Keq> 1 Rxn is favored towards C + D (the way it is written)!- if Keq< 1 rxn is favored towards A + B (reverse of the way its written)!- Says nothing about how fast (rate) equilibrium is achieved!!- Gibbs (derived) equation: relating equilibrium to the change in free energy (delta G)!- Delta G has no relationship to the rate at which a rxn will proceed!- Rxns w/delta G near zero = freely reversible - the greater the Keq, the most neg. your free energy (delta G) is3) Understand the difference between free energy of a rxn and standard free energy 4) Be able to solve simple problems determining the delta G of a coupled rxn from its component rxns - Delta G values are additive!- Keq values are multiplicative!- In our bodies we use rxns that couple so one isn't favorbale, 1 is very favorable.!!Delta G=
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