What is ATP's role in metabolism?

Three steps comprise cellular respiration, also known as metabolism:

ADP is phosphorylated later in glycolysis to become the active form of the molecule, ATP, which holds energy for the cell. Initially, during glycolysis, ATP is used to invest energy in glucose to allow for its subsequent breakdown into pyruvate.

The only time ATP is used in the Krebs Cycle is during its synthesis, which happens approximately halfway through the cycle's steps. During this process, a molecule called GDP—which is similar to ADP—is phosphorylated, which phosphorylates ATP.

As we move on to electron transport, ATP is mostly produced here. It is not spent during electron transport; rather, it is synthesized. A gradient builds up as hydrogen ions are pumped through the inner mitochondrial membrane's plasma membrane and into the mitochondria's intermembrane space.

As you probably already know about diffusion, these hydrogen ions will resist having this gradient and will want to return to the matrix, where there is a lower concentration of hydrogen ions. Essentially, this means that there are more hydrogen ions in the intermembrane space than in the matrix of the mitochondria (where the hydrogen ions started off).

However, ATP synthase, a protein located in the inner mitochondrial membrane, is the only pathway that allows the ions to enter the matrix. It functions by means of hydrogen ions attaching to a rotor on the upper portion of the protein, which causes the rotor and an attached rod to spin.

The rod is positioned within the protein's bowl-shaped structure, and when it spins, the binding sites within the bowl structure are triggered, causing ADP to be phosphorylated. Electron transport produces a large amount of ATP.

To summarize, you can think of ATP as a rechargeable battery for the cell, and metabolism replenishes the batteries. ATP is essentially the energy bearer for the cell during metabolism.

ATP serves as the primary energy currency in cells, powering metabolic processes such as biosynthesis, active transport, and muscle contraction. It provides the energy necessary for cellular functions by donating phosphate groups in reactions, releasing energy stored in its bonds.