Unit 5: Core Concepts and Kinetics

• Enzymes are often highly specific in which substrates they will bind to
• Uncatalyzed reaction is (kun s^-1) and has nothing in the numerator
• Catalyzed rate (K cat s^-1)
• Rate enhancement is how much better the reaction works with enzyme vs without enzyme (kcats^-1/kuns^-1)
• Kcat is fully saturated and when 1 copy of the enzyme could cause how many reactions (15rxn/sec)
• Because of enzymes like DNA polymerase, we need not HUGE amounts but SMALL amounts of dietary magnesium
• Kcat will tell us the reaction velocity for one copy of enzyme
• Actual relevant ΔG in your cells will differ somewhat on the actual conditions are pH, mammalian body temp...
• ΔG provides information about spontaneity but not rate
• Free energy (G) is a measure of the energy that is capable of doing work
• AN enzyme can greatly increase the rate of a spontaneous (ΔG<0 or exergonic reaction) by lowering the energy that is required to convert reactants to product
• If a reaction is nonspontaneous (ΔG>0 or endergonic), an input of free energy will be needed to drive the reaction (PPi to 2Pi+H20)
• At equilibrium, favorable reactions have high concentrations of product and vice versa. with a nonlinear relationship
• K'eq = [products]/[reactants] and the higher the value the more favorable it is
• Reaction with ΔG* = -30kJ/mol and K'eq = 100,000 is highly favorable such as ATP + H20 to ADP +Pi (High G value to low G value)
• Reaction with ΔG around 0kJ/mol and K'eq = 1 is -^- graph and example is isomerization of glucose-6-phosphate
• Reaction with ΔG* = +30kJ/mol and K'eq of 1/100,000 looks like --^ is unfavorable and example is ADP+Pi to ATP + H20
• Highly unfavorable reactions is ADP+phosphate to ATP
• The actual ΔG can differ from its ΔG* depending on the concentration of the reactants and products
• ΔG = ΔG* + RTln([products]/[reactants])
• Supplying reactant: Making [reactants] larger will give a smaller overall value for the fraction in the final term of the equation = larger value for (ln100 = 4.6) than (ln1/100 = -4.6)
• Reaction ΔG: Impacted by reactant vs product 'nature' and by their concentrations
• ΔG is teh final actual favorability or lack thereof of the rxn under consideration under relevant conditions of interest
• ΔG* is the favorability or lack thereof of the reaction under agreed-upon standard conditions. Factors in the 'nature' of the reactants and products
• [products]/[reactants] is the ratio that is often dramatically impacted by earlier and later steps in the pathway
• Kcat is enzyme parameter and has units 1/sec
• For one reaction, an enzyme can affect rate not total amount of product ever formed
• Enzymes do not alter the reaction equilibrium
• Enzymes alter only the reaction rate
• Equilibrium is eventually achieved with or without enzyme; relative concentrations are determined by the G value differences between products and reactants
• Enzyme increases reaction rate and decreases the time that elapses before equilibrium is reached
• Thermodynamically favorable to break peptide bons
• Enzymes accelerate reactions by facilitating the formation of the transition state
• Activation energy is needed for conversion of substrates to transition states
• Transition states are the intermediate states before products form
• Substrate to transition states to product
• • Activation energies have positive value because the G values of the transition states (eg. 10) minus the G value of the substrate (eg. 5) (Just image the graph so -^\-where first - is substrate and ^ is transition state and \- is product
• Enzymes tend to facilitate the formation of the transition state and stabilize it during its brief existence which lowers the state G value
• Enzyme-catalyzed reactions can have much lower activation energies than uncatalyzed reactions
• Formation of an enzyme-substrate complex is the first step in enzymatic catalysis