[Campbell Biology P.200] The text describes how the cell uses ATP to perform work, often inv... | Practice Question

The text describes how the cell uses ATP to perform work, often involving the formation of a 'phosphorylated intermediate.' What is the key role of this phosphorylated intermediate in coupling exergonic and endergonic reactions?

  • A: It directly provides heat to increase the kinetic energy of reactants, thereby speeding up the endergonic reaction.
  • B: It lowers the activation energy of the endergonic reaction, making it spontaneously occur.
  • C: It raises the free energy of the reactant molecule to which the phosphate group is transferred, making the subsequent step of the endergonic reaction exergonic.
  • D: It acts as a stable, non-reactive storage molecule for the released energy, preventing its dissipation.

Explanation

The text states: 'This usually involves phosphorylation, the transfer of a phosphate group from ATP to some other molecule, such as the reactant. The recipient molecule with the phosphate group covalently bonded to it is then called a phosphorylated intermediate. The key to coupling exergonic and endergonic reactions is the formation of this phosphorylated intermediate, which is more reactive.' The phosphorylation of the reactant makes it more unstable and reactive, effectively raising its free energy to a point where the subsequent reaction becomes exergonic.