Question

biochemisttry
2. (10 pts.) Hexokinase catalyzes the first reaction in glycolysis converting glucose to glucose 6-phosphate (G6P). This reaction, on its own (without the enzyme catalyst), has a ΔG’° = +13.8 kJ/mol, and is written as: Glucose + Pi → Glucose 6-phosphate + H2O The conversion of Glucose to G6P is dependent on the hydrolysis reaction of ATP to ADP, which has a ΔG’° = -30.5 kJ/mol, and is written as: ATP + H2O → ADP + Pi The overall conversion of Glucose to G6P, however, is a favorable reaction. This is possible by the coupling of the two reactions above. a. What do the sign and the value of ΔG’° for each reaction tell us about each of the reactions (6/10)? b. What are the two requirements for these reactions to be coupled (4/10)?

Answer 1

ANSWER :-

In the first step of glycolytic pathway, glucose is phosphorylated to glucose 6-phosphate. At the expense of one ATP

Glucose + ATP ---> Glucose 6-phosphate + ADP + H+

In most of the cell this reaction is catalyzed by hexokinase enzyme present in cell of all organism.

Hexokinase and pyruvate kinase, the other kinase of the glycolysis, like many of other kinase, require the presence of magnesium ion. Mg2+ requires for their activity. Mg2+ binds to the ATP to form the complex MgATP2-, and infact the true substrate of the enzyme is not ATP but this complex. it should be emphasized that the nucleophilic attack by a -OH group of glucose at a terminal phosphorus atom of the ATP is facilitated by the action of Mg2+ that interacts with the negative charges of the phosphoryl groups of the nucleoside triphosphate.

The formation of phosphodiester bond between a phosphoryl group and the hydroxyl group at the C-6 of glucose is thermodynamically unfavourable and requires energy to proceed, energy that is provided by the ATP. Indeed while the phosphorylation of glucose at C-6 by inirganic phosphate has a ∆G° of 13.8 kJ/mol (3.3kcal/mol) namely namely it is an endergonic reaction. , the hydrolysis of ATP to ADP and pi has ∆G° of -30.5 kJ/mol ( -7.3 kcal/mol), namely it is an exergonic reaction. The net reaction has ∆G° of ( -30.5 + 13.8 ) = -16.7 kJ/mol. So, ∆G° is negative. So,

a.) Sign is negative and the net value of ∆G° is -16.7 kj/mol.

b.) The two requirements for these reactions to be coupled are the Mg2+ and ATP or energy. MgATP2- complex.