lecture 3 - bioenergetics Flashcards
what is the dissociation constant? (Kd)
the reciprocal of the equilibrium constant (Kd = 1/Keq); how tightly a protein binds to its ligand
the lower the Kd…
the higher the binding affinity and the tighter the binding of a ligand to its receptor; the lower the ligand concentration needed to reach 50 percent of binding
allostery
binding of a molecule at one site on a macromolecule can change the three-dimensional shape of a distant site
exergonic
energy-releasing; products contain less energy than the reactants, occurs spontaneously
endergonic
energy-absorbing; products contain more energy than the reactants, not spontaneous
if delta G is negative…
the forward reaction (formation of products) will occur spontaneously, energy will be released
if delta G is positive…
the forward reaction will NOT occur spontaneously, energy must be added
if delta G is zero…
both forward and reverse reactions will occur; equilibrium
an exothermic reaction in which entropy increases…
occurs spontaneously
an endothermic reaction occurs spontaneously if…
entropy increases enough so the term can overcome the positive delta H
do enzymes alter the value of delta G?
no; they alter the activation energy
what does the velocity at which products are generated depend on?
the concentration of material in the transition state
the higher the activation energy…
the lower the fraction of reactants that reach the transition state, and the slower the overall rate of reaction
what does lowering the activation energy mean?
decreasing the difference in free energy between the reactants and the transition state
what does lowering activation energy result in?
acceleration of overall reaction rate
how can endergonic reactions occur spontaneously?
by coupling the reaction with another energy-releasing reaction to result in a negative delta G
example of energy-releasing reaction?
hydrolysis of ATP (-7.3 kcal/mol)
what type of bond contains useful energy in ATP molecule?
covalent bond; phosphodiester bonds
ligand
the molecule to which a protein binds
the stronger the interaction between a protein and ligand…
the lower the value of Kd
Michaelis-Menten enzyme-substrate-binding hypothesis
the rate of an enzymatic reaction was proportional to the substrate concentration at low substrate concentrations, but at high substrate concentrations, the rate reached a plateau (Vmax)
Michaelis constant (Km)
measure of the affinity of an enzyme for its substrate
what does the Km indicate?
the substrate concentration that yields a half-maximal reaction rate (1/2Vmax)
the smaller the value of Km…
the more effective the enzyme is at making product from smaller concentrations of substrate and the lower the substrate concentration needed to reach half-maximal velocity
competitive inhibition
Vmax stays the same, Km increases
noncompetitive inhibition
Vmax decreases, Km stays the same
3 amino acids that can be phosphorylated
serine, threonine, tyrosine
