Question

1. When ATP is hydrolyzed in vitro (i.e. in a test tube) to form ADP and inorganic phosphate, free energy is merely released as heat to the surroundings. In a cell this would be a wasteful use of energy and dangerous rising temperatures would lead to the denaturation of enzymes. How, then, do cells use the hydrolysis of ATP to perform cellular work? A complete response would include the following terms: energy coupling, endergonic/exergonic, phosphate transfer, and phosphorylated intermediate.

Answer 1

ATP is used as energy currency in the cell to drive the energy-requiring reactions. Mere hydrolysis of ATP also releases nothing but the heat inside the cell as well as in the test tube. The trick is reaction coupling or energy coupling, where exergonic reactions like ATP hydrolysis are coupled with endergonic reactions, via a shared intermediate. For ATP the shared intermediate is a phosphorylated intermediate. The overall change of Gibbs free energy of the coupled reaction is negative. A detailed explanation is attached below along with an example.
no 00.- o-p-o-p-o-p. ) 6-1 6-kov OH OH the High energy bonds. ATP is used as energy currency in cell, to pay energy requirement of energy requiring reactions. • Hydrolysis of ATP ATP & HO - ADP A Pi + energy es utilised This This ene energy by cell • AG of this rean is about (6) 30 kJ/mol. • So it is a spontaneous reaction. • Reaction Cupling Cell use Reaction Cupling energy copling to utiline the energy relieved by ATP. This is borically directly linking an energetically fevourable reaction (Ast = -re) (like ATP hydrolyris), wil an energetically unfavourable reaction de tre (endergenic rexn). A shared intermediate links there two reaction. The overall reaction is having (A) re value of AG. - A - B -0 AG = X here, B is the B ² CAD - intermediate AG=2 that couple no f no ② AG= (x+2) AT CAD Reactions.

provides on of ith phamph 3 power an endergenic reaction in cell, ATP on of its phamphate group, making a phosphonylated intermediate. • An example Formation of sucmore from glucose & energy requiring. ATP provides this energy. Glucose + Fructore - AG = + 27 kJ/mol Suemose ADP + Pi Are ATP + H₂O - AG = -30 W/ Glucose & Suemose & ADP + Pi fructore & ATP & + HO AG=-3 ks/mol The actual mechanism + Glucose ATP Gluess-P AOP Glucose P fructore Sure phosphorylated intermediate • The erragme that is involved in the coupled reaction first transfer the -PO4 gr. from ATP to make the phosphonylated intermediate. Urtemately the pi es rekared and final product forms.