Thermodynamics, Reaction Coupling, and Enzymes Flashcards
what is gibbs free energy equation
deltaG = deltaH - (deltaT)(deltaS)
What deltaG values make a rxn spontaneous and nonspontaneous?
Spontaneous/exergonic = deltaG <0
Nonspontaneous/endergonic = deltaG >0
what is deltaH?
enthalpy-it’s the potential energy
what is deltaS?
entropy-it’s the kinetic energy
distinguish between exergonic and endergonic
endergonic = release of heat
exergonic = release of any type of energy
all endergonic rxns are exergonic, but not all exergonic rxns are endergonic
what is reaction coupling?
refers to coupling an endergonic rxn to an exergonic rxn to make a rxn proceed in the forward direction and thus making the overall rxn spontaneous
____ hydrolysis is coupled with other rxns to drive other endergonic rxns within the body
ATP
what does kinetics refer to?
how fast something will happen. thus, if you want to know how fast a rxn will go, you look at kinetic factors like transition state and activation energy.
the higher the transition state (aka the higher the activation energy), the ____ (faster or slower) the rxn will occur
slower
the energy difference between your reactants/reagents and your products is your ____
deltaG
catalysts increase the rate of the rxn by _____ the transition state and reducing the ______ ______
stabilizing the transition state
reducing the activation energy
why do catalysts not act in the thermodynamic region of the rxn and therefore do not affect deltaG?
because they cannot make a nonspontaneous rxn spontaneous; they can only make rxns happen faster.
In order to be considered an enzyme, the enzyme must do what 3 things?
increase the rate of the rxn, not be used up in the rxn, and be specific for a particular rxn
If an active site on an enzyme is negatively charged, what type of substrate will it bind to?
a positively charged substrate
when an enzyme is turned “off,” it can be referred to as being in the ____ state
tense
an enzyme in the on position is also referred to as being in the ____ state
relaxed
what is the number one way to regulate enzyme activity?
phosphorylation (a type of covalent modification)
what is the second most common way to regulate enzyme activity?
allosteric regulation (regulator binds to the allosteric site, which is any site on the enzyme that is not the active site)
how are zymogens activated?
by proteolytic cleavage of one of its peptide bonds
what does the feed forward mechanism refer to?
a lot of reactant will stimulate the rxn forward
what is a V vs. S graph
looks at the affect of various concentrations of substrate on a constant concentration of enzyme
V vs. S graph: If substrate concentration is substantially low and then doubled, what will the rate of product do?
it will also double
V vs S graph: What is Vmax
signals the max production rate under those particular conditions shown on the graph (this is the point on the graph where the slope levels off)
Vmax only depends on (or can be affected by) the ______ concentration and the type of ____ being used
enzyme, enzyme
V vs S graph: What is Km?
the substrate required to reach 1/2 of Vmax, and can be related to level of affinity the enzyme has on its substrate
If an enzyme has an increased affinity for its substrate, how will Km be affected?
Km will decrease
Enzyme inhibition: distinguish between competitive, noncompetitive, uncompetitive, and mixed inhibition
competitive inhibitor: binds at the active site of the enzyme so the substrate can no longer bind onto the active site itself
non-competitive inhibitor: binds to the allosteric site; substrate can still bind to the enzymes active site, but the enzyme won’t be able to process or react with the enzyme
uncompetitive: binds to the allosteric site of the enzyme-substrate complex, which makes the substrate locked into that active site.
mixed inhibitor: can bind to the enzyme alone or the enzyme-substrate complex; can also sometimes change the active site, making it harder for the substrate to bind to the enzyme, if it can at all.
How to competitive, non-competitive, uncompetitive, and mixed inhibition affect Vmax and Km?
competitive: Km increases, Vmax stays the same (because if you increase the substrate concentration high enough, it can out-compete the inhibitor)
non-competitive: Km stays constant, Vmax decreases
uncompetitive: Km decreases, Vmax decreases
mixed: Km varies, Vmax decreases
what is the lineweaver-burk plot of V vs S?
a reciprocal (aka inverse) plot of V vs S
V vs S Lineweaver-Burk Plot: the bigger the Vmax value, the _____ the y-axis intercept value will be on the reciprocal plot
smaller
Lineweaver-Burk plot: For allosteric inhibition, Vmax is a smaller number on a regular V vs S plot, which means that it will intersect the y-axis at a ____ (higher or lower) value compared to the uninhibited rxn
higher
Lineweaver-Burk Plot: The larger the value of Km, the more x-axis intercept value will be to the ____ (right or left) compared to the uninhibited rxn.
right
Enthalpy (potential energy) is stored in _____ of molecules
bonds
what is the kinetic energy component of the gibbs free energy equation?
(deltaT)(deltaS)
Can the change of substrate concentration affect Vmax?
no
An anti-substrate antibody would decrease concentration of substrate, which means there is less substrate that the enzyme can bind to. How would this affect Km and Vmax
Km would increase because the ability for the enzyme to bind to its substrate decreases, as there is less substrate to bind to. Vmax stays the same because the enzyme hasn’t lost it’s affinity for the substrate (remember Vmax is never altered by substrate concentration).
