ATP is made when energy, raw materials, and the right enzyme system all come together in the cell.

Core idea: what must come together

To synthesize ATP, a cell must bring together:

  • ADP (adenosine diphosphate), which is the “partially charged” nucleotide.
  • Inorganic phosphate (PiP_iPi​), which will be added onto ADP.
  • A source of energy to drive the bonding of ADP and PiP_iPi​.
  • The enzyme ATP synthase (or another ATP‑forming enzyme) to catalyze the reaction.
  • The correct environment (membranes, gradients, or substrates) so the enzyme can work.

In mitochondria: oxidative phosphorylation

For most ATP in cells, all of this comes together in mitochondria through oxidative phosphorylation.

What is needed:

  • A supply of high‑energy electrons from NADH and FADH2_22​, generated by glycolysis and the citric acid cycle.
  • An intact inner mitochondrial membrane containing the electron transport chain and ATP synthase.
  • Oxygen as the final electron acceptor to keep electrons flowing through the chain.
  • A proton (H +^++) gradient across the inner membrane; as protons flow back through ATP synthase, the enzyme uses that energy to join ADP and PiP_iPi​ into ATP.

In short, ATP is made when ADP and phosphate meet ATP‑forming enzymes in the right structural setting (like a membrane with a proton gradient) and are supplied with energy from redox reactions or high‑energy substrates.

describe what must come together in order for ATP to be made: ADP + PiP_iPi​ + energy + ATP‑forming enzyme (often ATP synthase) in the proper cellular environment.

TL;DR: ATP forms when ADP and inorganic phosphate are brought together by ATP‑producing enzymes and powered by energy from respiration, usually using a proton gradient across a membrane in mitochondria.

Information gathered from public forums or data available on the internet and portrayed here.