Assume that you have a solution of 0.1M glucose-6-phosphate. To this solution, y
ID: 51709 • Letter: A
Question
Assume that you have a solution of 0.1M glucose-6-phosphate. To this solution, you add the enzyme phosphoglucomutase, which catalyzes the following reaction:
Glucose-6-P <-----> Glucose-1-P (G0 = +1.8 kcal/mol)
1} Does this reaction proceed at all as written ? (hint: work the problem, then answer this question)
2) What are the final concentrations of reactants and products if the reaction is allowed to proceed to equilibrium. (hint: you need algebra for this one)
3) If you were designing a factory which needed a continual, high rate of glucose-1-phosphate and you had only glucose-6-phosphate and phosphoglucomutase as starting materials what would you do? (hint: you can't add significantly to your costs i.e. no fair adding energy)
Explanation / Answer
Question 1: Does this reaction proceed at all as written?
Answer 1: G, the Gibbs free energy which is equal to the total amount of energy capable of doing work during a process at constant temperature and pressure. In a simpler term it is defined as energy associated with chemical reaction that can be used to do work.
G is expressed as change in gibbs free energy of the system that occurs during a reaction which is expressed as
G : H+TS
and when this reaction occur under standard conditions the change in gibbs free energy is termed as Standard-state free energy of reaction (G0)
G0: H0+TS0
In the given reaction, the change is gibbs free energy is expressed as G0 which signifies that is the reaction took place at standard conditions i.e temperature: 25oC and pressure:1 atm
Glucose-6-P <-----> Glucose-1-P (G0 = +1.8 kcal/mol)
Here G0 has positive value of 1.8 kcal/mol which signifies that reaction is nonspontaneous because when
• If G is negative, then the process is spontaneous and termed exergonic.
• If G is positive, then the process is nonspontaneous and termed endergonic.
• If G is equal to zero, then the process has reached equilibrium
The given reaction requires the input of energy to proceed the reaction in the normal forward direction.
Question 2: What are the final concentrations of reactants and products if the reaction is allowed to proceed to equilibrium.
Answer 2: During the reaction when the concentration of the product to the reactant changes from the standard condition then the non standard free energy describes the present system i.e G. The relationship between the free energy of reaction at any moment in time (G) and the standard-state free energy of reaction (G0) is described by the following equation.
G = G0+ RT ln Q
Where
R is the ideal gas constant ( J/mol-K)
T is the temperature (K)
ln represents a logarithm to the base e,
Q is the reaction quotient at that moment in time
Q=
At equilibrium the change in the product to reactant will fall under standard condition therefore G = 0 and Q will be expressed as Keq
So the equation G= G0 + RT ln Q will be expressed as
0 = G0+ RT ln Keq
We can therefore solve this equation for the relationship between Go and K.
G0 = - RT ln Keq
Here G0 = +1.8 kcal/mol (convert it to joule/ mol by multiplying it with 4184, because 1 calorie is equivalent to 4184 joule; 7531.2 J/mol), R is 8.314 J/mol K and T is 298 K so
In Keq= -(7531.2 J/mol)/(8.314j/mol K x 298K)
In Keq= -3.039
2.303 x log (Keq) = -3.039
Log (Keq) = -(3.039/2.303)
Keq= 0.0479
Q= =Keq
Glucose 6 phosphate is 0.1 M there fore
Glucose 1 phospahte is=Keq x [glucose 6 phosphate]
=0.0479 x0.1
=4.79 X 10 -3
Question 3:If you were designing a factory which needed a continual, high rate of glucose-1-phosphate and you had only glucose-6-phosphate and phosphoglucomutase as starting materials what would you do?
Phosphoglucomutase is a enzyme which effects a phosphoryl group shift by exchanging a phosphoryl group with the substrate (-D-glucose monomer ) from the 1' to the 6' position or the 6' to the 1' position.
To increase the rate of product formation (glucose 1 phosphate) we have to increase the concentration of substarte. As the concentration of substrate will increases, the enzyme becomes saturated with substrate. As soon as the catalytic site is empty, more substrate is available to bind and undergo reaction. Apart from that we have to maintain optimum condition for the enzyme i.e pH and temperature. Phospho glucomutase requires metal ion so we have to provide metal ions in the reaction medium.