ATP — The Energy Molecule

ATP (adenosine triphosphate) is the energy molecule that supplies immediate energy for muscle action. It consists of a large molecule called adenosine plus three simpler components called phosphate groups. When a phosphate is removed, energy is released to do biological work — including muscular contraction, nerve conduction, and secretion.

In muscle, this energy is used by the crossbridges to pull the actin filaments across the myosin filaments, causing the muscle to shorten.

The breakdown and resynthesis cycle:

• ATP → ADP + Pi + Energy (energy released to do work)
• ADP + Pi + Energy → ATP (resynthesis, using energy from foods and phosphocreatine)

Abbreviations used in the source:

• ATP = adenosine triphosphate
• ADP = adenosine diphosphate
• Pi = inorganic phosphate

The building blocks for ATP synthesis are exactly the by-products of its breakdown (ADP and Pi); the energy for resynthesis comes from the breakdown of foods and of phosphocreatine, coupled to the energy needs of the resynthesis reaction.

• ATP = adenosine + three phosphate groups.
• Removing a phosphate releases energy for work.
• Powers muscle contraction, nerve conduction, and secretion.
• In muscle: energy used by crossbridges to pull actin across myosin.
• ATP ⇌ ADP + Pi + Energy.
• Resynthesis fueled by foods and phosphocreatine.

• phosphocreatine-breakdown — PC donates phosphate to rebuild ATP.
• atp-pc-system — ATP and PC as the immediate stored energy source.
• skeletal-muscle-structure — actin/myosin filaments the crossbridges act on.
• active-tension — tension from crossbridge formation and actin/myosin movement.