Question

pyruvate kinase is a major enzyme involved in energy metabolism. pyruvate kinase couples two reactions:

1. removing a phosphate group from an intermediate called phosphoenolpyruvate (pep) to form another intermediate called pyruvate.
2. addition of a phosphate group to adp to form atp.

reaction 2 is highly non - spontaneous, but the overall reaction catalyzed by pyruvate kinase is spontaneous. which conclusions are supported by this information? select all that apply.
both reaction 1 and reaction 2 are non - spontaneous.
the chemical bond broken in pep has higher potential energy than the chemical bond formed in atp.
pep has higher free energy than adp.
pep has higher free energy than pyruvate.
reaction 1 releases more free energy than reaction 2 absorbs.

Explanation:

• For the second option: In coupled reactions, the energy - releasing reaction (reaction 1) provides energy for the energy - requiring reaction (reaction 2). If the overall reaction is spontaneous, the energy from the bond broken in PEP (in reaction 1) must be greater than the energy used to form the bond in ATP (in reaction 2).
• For the fourth option: Since reaction 1 is the breakdown of PEP to pyruvate (a reaction that releases energy as it is part of a coupled spontaneous reaction), PEP has higher free energy than pyruvate.
• For the fifth option: In a coupled reaction where the overall reaction is spontaneous (\(\Delta G_{total}<0\)), if \(\Delta G_1\) (for reaction 1) and \(\Delta G_2\) (for reaction 2) are the free - energy changes of the two reactions, \(\Delta G_{total}=\Delta G_1+\Delta G_2<0\). Since reaction 2 is non - spontaneous (\(\Delta G_2>0\)), then \(\vert\Delta G_1\vert>\vert\Delta G_2\vert\), meaning reaction 1 releases more free energy than reaction 2 absorbs.

Answer:

The chemical bond broken in PEP has higher potential energy than the chemical bond formed in ATP; PEP has higher free energy than pyruvate; Reaction 1 releases more free energy than reaction 2 absorbs.