Why does assembling macromolecular complexes require energy?

• A. It is exergonic and increases entropy.
• B. It requires energy and decreases entropy.
• C. It occurs spontaneously without energy input.
• D. It is endergonic and decreases entropy.

Answer: (D)

Assembling a macromolecular complex creates a more ordered, specific structure from separate parts. That increase in order means a decrease in the system’s entropy, which thermodynamically makes the process non-spontaneous on its own. To push this assembly forward, energy must be supplied, so the overall change in Gibbs free energy is positive unless energy is coupled to the process. In cells, this coupling often comes from ATP or GTP hydrolysis, providing the work needed to form bonds and arrange subunits precisely. So, the formation is endergonic and decreases entropy, requiring an input of energy to occur.