3. Coupling of the two reactions below leads to the transfer of a phosphate (Pi)

Question

3. Coupling of the two reactions below leads to the transfer of a phosphate (Pi) from phruvate (PEP) to ADP and the synthesis of ATP and pyruvate (PYR) in the last step of glycolysis. PEP + H2O PYR + Pi G":-14.8 kcal/mol ADP + Pi ATP + HsO Go,7.3 kcal/mol Part A: Write a single reaction for the phosphorylation of ADP by the transfer of a phosphate group from PEP. (2 pts) Part B: Name the major class of enzymes that would catalyze this type of coupled reaction. (2 pts) Part C: Determine &Go;, for the coupled reaction. (2 pts) Part D: Calculate K'e for the coupled reaction. (3 pts) Part E: In human erythrocytes, the steady-state concentration of ATP is 2.24 mM, ADP is 025 mM, and pyruvate is 0.051 mM. Calculate the concentration of PEP at 25C, assuming that the reaction is at equilibrium in the cell. (5 pts) Part F: The physiological concentration of PEP in human erythrocytes is 0.023 mM. Compare this s with the value obtained in Part E (show calculation). What is the significance of this difference2 Explain. (3 pts)

Explanation / Answer

ANS:

A) Pyruvate kinase

Phosphoenol pyruvate --------------------------------------> Pyruvate

ADP+Pi -----> ATP

The above reaction catalysed by the enzyme pyruvate kinase , in presence of magnesium ion (Mg+2)

B)

The class of enzyme that associated with copled reaction in Oxidoreductase:

Oxidoreductases catalyze oxidation reduction reactions. At least one substrate becomes oxidized and at least one substrate becomes reduced

C)

Free energy coupling refers to the rule that the free energy changes of coupled reactions are additive.

As long as the overall G is negative, both reactions can take place. Even a very endergonicreaction can occur if it is paired with a very exergonic one (such as hydrolysis of ATP)

D)

Km is defined as the substrate concentration at which the reaction velocity is half maximal.

It is a linear function of the ratio between the Km of the coupled intermediate for the second enzyme and the units of the second enzyme added, when the coupling enzyme operates in the first-order region; that is: 2. L = Kb/V 2

E) Concentration pyruvate is 0.051 mM

at equilibrium condition the phosphoenol pyruvate will give similar number of pyruvate.

F) if the concentration of phosphoenol pyruvate in erythocyte 0.023, this difference indicates that in erythrocyte

G)

The increase in the rate of formation of phosphoenolpyruvate is primarily responsible for the in- crease in its rate of reaction in the kinase step. Phosphoenolpyruvate was transported through the erythrocyte membrane at low pH

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