Organic Compounds - ATP

Function:

• Adenosine triphosphate (ATP) is used throughout the cell.
• ATP provides energy for the cell to do work.
  • mechanical work - move cilia, vesicles, etc.
  • transport work - across the membrane(s).
  • chemical work - force non-spontaneous reactions.

Structure:

• ATP is composed of phosphate groups, a ribose and adenine.
• Adenosine monophosphate (AMP) is a monomer of RNA.
• Adding additional phosphate groups yields an unstable molecule.
• Negatively charged phosphates repel one another.
• The bond is easily broken by hydrolysis.
• ATP + H₂O ADP + PO₄^-
• Energy yield is approximately -10 kcal/ mol

ATP-ADP Cycle:

• ATP usually gives the PO₄^- to another molecule.
• The new molecule is said to be phosphorylated.
• That new molecule is even more unstable and quickly does "something".
  • a motor protein moves.
  • a membrane protein transports a solute.
  • a different chemical reaction proceeds.
• The ATP becomes ADP. ADP is more stable.
• ADP is phosphorylated to become ATP, completing the cycle.

Some Numbers:

• In one minute a working muscle cell uses 10,000,000 ATP molecules.
• That is the cell's entire supply, so ADP must be recycled into ATP.
• Even resting in bed, you use 20 kg of ATP every 24 hours!