biochemisttry 2. (10 pts.) Hex

biochemisttry2. (10 pts.) Hexokinase catalyzes the first reaction in glycolysisconverting glucose to glucose 6-phosphate (G6P). This reaction, onits own (without the enzyme catalyst), has a ΔG’° = +13.8 kJ/mol,and is written as: Glucose + Pi → Glucose 6-phosphate + H2O Theconversion of Glucose to G6P is dependent on the hydrolysisreaction of ATP to ADP, which has a ΔG’° = -30.5 kJ/mol, and iswritten as: ATP + H2O → ADP + Pi The overall conversion of Glucoseto G6P, however, is a favorable reaction. This is possible by thecoupling of the two reactions above. a. What do the sign and thevalue of ΔG’° for each reaction tell us about each of the reactions(6/10)? b. What are the two requirements for these reactions to becoupled (4/10)?



In the first step of glycolytic pathway, glucose isphosphorylated to glucose 6-phosphate. At the expense of oneATP

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

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

Hexokinase and pyruvate kinase, the other kinase of theglycolysis, like many of other kinase, require the presence ofmagnesium ion. Mg2+ requires for their activity. Mg2+ binds to theATP to form the complex MgATP2-, and infact the true substrate ofthe enzyme is not ATP but this complex. it should be emphasizedthat the nucleophilic attack by a -OH group of glucose at aterminal phosphorus atom of the ATP is facilitated by the action ofMg2+ that interacts with the negative charges of the phosphorylgroups of the nucleoside triphosphate.

The formation of phosphodiester bond between a phosphoryl groupand the hydroxyl group at the C-6 of glucose is thermodynamicallyunfavourable and requires energy to proceed, energy that isprovided by the ATP. Indeed while the phosphorylation of glucose atC-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 ATPto ADP and pi has ∆G° of -30.5 kJ/mol ( -7.3 kcal/mol), namely itis 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 -16.7kj/mol.

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

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