Exam 2
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Free Energy
The energy that is available to be used by a system
Change in Free Energy
The difference between the initial amount of free energy and the final amount of free energy. (delta) G = Gf - Gi
Reactants
The initial state of the chemical system initial free energy (Gi)
Products
The final state of the chemical system (Gf)
Spontaneous
Inherent tendency for a process to go in a particular direction
Spontaneous (exergonic reaction)
Inherent tendency the thermodynamically favorable
Not spontaneous (endergonic reaction)
No inherent tendency - Not thermodynamically favorable
Spontaneous (delta G)
the answer should be negative
Not spontaneous (delta G)
the answer should be positive
Keq (equation)
[products] / [reactants] (under physiological conditions, delta G > 0)
Keq^prime (equation)
[products] / [reactants] (under standard conditions)
delta G (equation)
delta G^prime + RTlnkeq (R = 1.987x10^-3Kcalmol^-1K^-1) (T = 310 K)
delta G^prime (equation)
-(R)(T)^prime(ln(keq^prime)) (R = 1.987x10^-3Kcalmol^-1K^-1) (T = 298 K)
What enzymes are and what they do
• Increase the rate of biochemical reactions by reducing the energy of activation, Ea. • Enzymes are unique to a given reaction in most cases, “one enzyme - one substrate.” • As catalysts, enzymes emerge from the reaction unchanged, so they are recycled in the reaction, so only a small [E] is sufficient.
What enzymes DO NOT DO
• Do not change the equilibrium conditions, do not change keq of a reaction. • Do not change delta G, and do not change endergonic into exergonic reaction. • Do not supply energy to drive an endergonic reaction.
Enzymes are
They are globular proteins
Two types of the prosthetic groups
• Cofactor: small, inorganic molecule or ion. • Coenzyme: organic molecules B vitamins and vitamin C
Enzymes
Catalysts of biochemical reactions
Important points about delta G
• Reversible, same amount: A -> B, delta G = -5Kcalmol^-1K^-1 (exergonic) B -> A, delta G = +5Kcalmol^-1K^-1 (endergonic) • If delta G = 0, then the system is at equilibrium, and no net reaction is occurring. • The total free energy change of a pathway depends only on the difference between the initial Gi and the final Gf and not on the path taken: A -> B -> C -> D.
Ea (energy of activation)
“energy barrier” measure of stability
Prosthetic group
helps to activate the enzyme
Active site
folder groove
Enzyme activity
Environmental factors affect the shape of the enzyme protein, therefore its function
pH of solution (graph)
• stomach enzymes (pepsin, rennin) adapted to acid conditions (more towards pH = 1) • most enzymes have optimum function near neutral pH • changes in pH can quickly alter bonding patterns and reduce function of enzyme