1. Biochemistry Basics Flashcards
What is the first law of thermodynamics?
The law of conservation of energy. The energy of the universe is constant.
If the energy of a system decreases, than the energy of the universe (surroundings) increases, and vice versa,
What is the second law of thermodynamics?
Entropy –> the universe tends towards randomness (i.e. increased entropy)
If entropy (S) has a negative sign, what is true?
a negative entropy means that entropy has decreased, which is an unfavorable event (the universe wants increases in entropy)
What is the equation for Gibbs free energy?
ΔG = ΔH - TΔS
free energy = G
enthalpy (heat of reaction) = H
T is temperature in kelvin
S is entropy
explain exergonic and endergonic?
exergonic reaction, ΔG is negative, and the reaction is spontaneous.
endergonic reaction, ΔG is positive, and the reaction is non-spontaneous.
what are exothermic and endothermic?
exothermic, negative ΔH, release heat
endothermic, positive ΔH, require heat
how do you assign the signs (+/-) to quantities in a thermodynamic system?
signs are relative to the system NOT the surroundings.
so if the system releases heat, it is -ΔH
What is the standard free energy change?
(∆Gº and ∆Gº’)?
What is the equation for ∆Gº’?
The ∆G of a reaction also depends on the concentrations of reactants and products. To compare reactions, the
∆Gº has all R’s and P’s at 1M concentration.
Under physiological conditions, we need to further standardize because of H+ and pH. This refers to ∆Gº’.
∆Gº’ = -RTlnK’eq
Keq is the equilibrium constant for the particular reaction.
What is the formula for K’eq?
A + B –> C + D
K’eq = [C][D] / [A][B]
to the power of coefficients
if ∆Gº’ is standardized, what equation do we use to find the real ∆G of a reaction in the body?
∆G = ∆Gº’ + RTlnQ
where Q = [products] / [reactants]
∆Gº’ = -RTlnK-eq
What occurs if K’eq = 1? What occurs if Q=1?
recall, ∆Gº’ = -RTlnK’eq
if K’eq = 1, than ln(1) = 0
therefore, ∆Gº’ = 0.
recall ∆G = ∆Gº’ + RTlnQ
If Q = 1, than lnQ = 0
therefore, ∆G = ∆Gº’
What is the core difference between K and Q?
Q is the ratio of reactants and products in any given situation. K is the ratio of reactants and products at equilibrium.
What is equilibrium?
The rate of the forward and reverse reactions are equal. NOT the concentrations.
t or f, if a reaction is at equilibrium then overall concentrations stay the same.
TRUE, since the rate of reaction in both directions is equal, concentrations on each side remain what they are (but not necessarily the same [] on each side)
explain reaction shifts when…
- Q = K
- Q > K
- Q < K
- Q = K: the []’s are the same as equilibrium conditions, therefore, we are at equilibrium
- Q > K: Currently there is more product, and so there is a left shift towards reactants.
- Q < K: Currently there is more reactant, and so there is a right shift towards products.
more details on equilibrium and thermodynamics in general chemistry review.
What does a large K’eq indicate?
products / reactants. If equilibrium is achieved at a high k’eq, then products must have lower free energy than reactants.
Explain if ∆G=0.
Recall,
∆G = ∆Gº’ +RTlnQ
if ∆G = 0, than ∆Gº’ = -RTlnQ
this means, Q = K, which means we are at equilibrium.
What does spontaneous mean?
A reaction is favorable (∆G is negative). However, spontaneity says nothing about reaction rate!!
E.g. beta-decay of carbon –> this is favorable, but takes years to occur.
t or f, ∆G depends on the pathway the reaction takes and the rate of that reaction.
False! ∆G is simply a measurement of the difference in free energy between R’s and P’s. It is path-independent.
compare ∆G of oxidizing sugar in your body vs. an industrial furnace.
∆G is path-independent, and thus, is the same value in both cases. (the likely only difference is heat)
