ATP: the molecule that distributes energy

Molecules (Interaction and interdependence) · Cell respiration · note 1 of 3

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ATP: the molecule that distributes energySpec C1.2.1, C1.2.2, C1.2.3

In short

ATP, adenosine triphosphate, is a nucleotide that distributes energy within cells. Hydrolysis of ATP to ADP and phosphate releases enough energy for many tasks, such as active transport, synthesis of macromolecules and movement of cells or chromosomes. Synthesising ATP from ADP and phosphate requires energy, which comes from cell respiration.

ATP (adenosine triphosphate) is the molecule that distributes energy within cells. It is a nucleotide, made of the base adenine, the pentose sugar ribose and a chain of three phosphate groups.

ATP is a nucleotide: adenine, ribose and three phosphates. Hydrolysis of the terminal phosphate releases energy.

Why ATP suits its role as energy currency

It is soluble in water, so it moves easily to wherever energy is needed in the cell.
It is stable at the pH of a cell and does not break down unless an enzyme catalyses it, so energy is not wasted.
It cannot pass freely through membranes, so it stays inside the cell where it was made.
Hydrolysis of one phosphate group releases an amount of energy that is sufficient for many tasks in the cell, without releasing so much that most is wasted as heat.
It is rapidly regenerated from ADP and phosphate, so a small pool of ATP can be recycled many times.

Life processes that ATP supplies with energy

Active transport across membranes, for example pumping ions against their concentration gradient.
Synthesis of macromolecules (anabolism), such as proteins, DNA and glycogen.
Movement: of the whole cell (for example muscle contraction, cilia and flagella) or of cell components such as chromosomes during cell division.

Interconversion of ATP and ADP

ATP + H₂O → ADP + Pi (energy released)

Energy is released by hydrolysis of ATP to ADP (adenosine diphosphate) and phosphate. Energy is required to synthesise ATP from ADP and phosphate. In cells this energy comes from cell respiration (and in photosynthetic cells also from light). Often the phosphate removed from ATP is transferred to another molecule, making it more reactive.

Common mistake:

ATP does not store large amounts of energy long term; it distributes energy. Fats and carbohydrates are the energy stores.

Written and checked against the IB Biology SL specification · Updated October 2026

Frequently asked questions

Why is ATP called the energy currency of the cell?

ATP is called the energy currency because it distributes energy within cells. It is soluble, stable without enzymes and stays inside the cell, and hydrolysis to ADP and phosphate releases enough energy for tasks such as active transport, building macromolecules and movement. It is quickly regenerated from ADP using energy from respiration.

What is the difference between cell respiration and gas exchange?

Cell respiration is a set of enzyme-catalysed reactions inside cells that produce ATP using energy from carbon compounds. Gas exchange is the diffusion of oxygen and carbon dioxide between an organism and its environment, for example in the lungs. Gas exchange supplies oxygen for aerobic respiration and removes the carbon dioxide it produces.

What are the differences between aerobic and anaerobic respiration?

Aerobic respiration needs oxygen and mitochondria, can use carbohydrates, lipids and amino acids, gives a large yield of ATP and produces carbon dioxide and water. Anaerobic respiration in humans needs no oxygen, happens only in the cytoplasm, uses only glucose, gives just 2 ATP per glucose and produces lactate.