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18 Cards in this Set

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what is free energy?
energy in system available to perform work (includes thermal energy and entropy)
what must ΔG be for a reaction to spontaneouly form products?
negative
what does a positive ΔG indicate?

what if ΔG=0?
the reverse of the rxn will be spontaneous (reactants will form from the products).
System is at equilibrium.
what does ΔG depend upon and not depend upon?
the specific reactants and products of a reaction. It is independent of the pathway that is followed to convert the reactants to the final products.
what does ΔG tell nothing about?
rate of the rxn.
what determines the rate of a rxn?
the pathway determines the rate. The difference in free energy between the substrate (S) and the transition state (S*) is called ΔG‡ and determines the rate (the activation energy)
what do changes in ΔG‡ result in?
If ΔG‡ increases, then the rate of the reaction gets slower
If ΔG‡ decreases, then the rate of the reaction gets faster
how does an enzyme speed up rxns?
what is an enzyme?
decreases the free energy of the transition state.
Enzymes are molecules that accelerate specific biochemical reactions without themselves being altered.
They act as molecular catalysts, and are usually proteins (some enzymes are RNA molecules).
what are the general properties of enzymes?
specificity (type rxn and specific substrate), has active site where rxn chemistry occurs, substrate binding (can involve both noncovalent and transient covalent bonds)
Multiple weak interactions (ionic, hydrophobic, etc) mediate
the binding of the transition state to the active site.
what is Km (the Michaelis constant)?
the substrate concentration at which velocity = 1/2 Vmax
what does a large/small Km indicate about the enzyme?
An enzyme with a small Km indicates that the reaction can reach half its maximum velocity at low
substrate concentrations. This enzyme has a high affinity for the substrate.
An enzyme with a large Km indicates that the reaction can reach half its maximum velocity only at
high substrate concentrations. This enzyme has a low affinity for the substrate.
what are two major classes of inhibitors? and what are their characteristics?
competitive and non-competitive


Competitive Inhibitors. These are molecules that look like the natural substrate of an enzyme and bind
to the active site and compete for binding with the substrate. Since an enzyme is designed to bind the
transition state, an ideal competitive inhibitor mimics the transition state
A competitive inhibitor increases the Km of an enzyme but does not change the Vmax. In other words, the
enzyme is just as active on the substrate, but a higher concentration of substrate is needed to get binding to
the enzyme to produce product.


Non-Competitive Inhibitor. These are molecules that bind to a site on the enzyme that is different from
the active site. The activity of the enzyme is reduced when bound to a non-competitive inhibitor.
A non-competitive inhibitor reduces the Vmax without changing the Km of an enzyme. In other words, the
enzyme can bind the substrate with equal affinity, but it can’t convert the substrate to product as efficiently
with the non-competitive inhibitor bound to it.
what does KI mean for a competitive inhibitor?
Non-Competitive Inhibitor. These are molecules that bind to a site on the enzyme that is different from
the active site. The activity of the enzyme is reduced when bound to a non-competitive inhibitor.
A non-competitive inhibitor reduces the Vmax without changing the Km of an enzyme. In other words, the
enzyme can bind the substrate with equal affinity, but it can’t convert the substrate to product as efficiently
with the non-competitive inhibitor bound to it.
what does KI mean for a non-competitive inhibitor?
When the concentration of the inhibitor [I] equals the
KI, then the velocity of the reaction is decreased by a factor of two at every substrate concentration.
Explain how coupling of reactions works and affects delta G
In circumstances where the product of one reaction is the reactant in another reaction, the two
reactions are coupled. The ΔG’s for each individual reaction within coupled reactions are additive.
what is ΔG°’?
the ‘standard free energy’

the free energy change associated with the specific reactants under standard conditions where the
reactants and products are present at 1 M concentrations (this is ΔG°). pH = 7,
what is ΔG° used for?
you can predict whether a reaction is spontaneous under standard conditions
what is a real world example of coupling?
using the highly favorable hydrolysis of ATP to make the first step of
glycolysis favorable