What is ATP's role in metabolism?
ATP serves as a bearer of chemical energy in metabolism, more specifically in cellular respiration.
Cellular respiration (metabolism) comes in three steps:
- the Krebs Cycle
- the electron transport chain
During glycolysis, ATP is first used to invest energy in glucose, as to allow for its subsequent breakdown into pyruvate. Later in glycolysis, ADP is phosphorylated and becomes the active form of the molecule, ATP, which holds energy for the cell.
During the Krebs Cycle, ATP isn't used as much. In fact, the only time it is involved is with its synthesis, which occurs about halfway through the steps of the Krebs Cycle. A molecule similar to ADP, called GDP, is phosphorylated, which, in turn, phosphorylates ATP.
Moving on to electron transport, ATP is mainly produced here. It is not spent at all during electron transport, only synthesized. As hydrogen ions are pumped though the plasma membrane of the inner mitochondrial membrane into the intermembrane space of the mitochondria, a gradient build up.
This basically means that there are more hydrogen ions in the intermembrane space than in the matrix of the mitochondria (where the hydrogen ions started off). As you probably know about diffusion, these hydrogen ions are going to resist having this gradient, and they'll want to go back into the matrix, where there is a lower concentration of hydrogen ions.
But the only way for the ions to enter the matrix is through a protein in the inner mitochondrial membrane called ATP synthase. How that works is the hydrogen ions attach to a rotor on the upper part of the protein, which makes the rotor and an attached rod spin.
The rod sits in a bowl-like structure of the protein, and when the rod spins, the binding sites in the bowl structure are activated, which allows ADP to become phosphorylated. Electron transport yields many ATP
In summary, ATP is basically the energy bearer for the cell as metabolism takes place. you can think of it as a rechargeable battery for the cell, and metabolism recharges the batteries.