ATP (adenosine triphosphate) is the immediate source of energy in all cells. It is a phosphorylated nucleotide made of the base adenine, the pentose sugar ribose and three phosphate groups.Energy is released when the bond to the last phosphate group is broken by hydrolysis, catalysed by the enzyme ATPase:ATP + H2O → ADP + Pi + energy Here ADP is adenosine diphosphate and Pi is inorganic phosphate. About 30.5 kJ of energy is released per mole of ATP hydrolysed. The Pi can be transferred to another molecule (phosphorylation), making it more reactive.
ATP is remade from ADP and Pi by ATP synthase in a condensation reaction, using energy from respiration (and from light in photosynthesis).ATP suits its role because:
• it releases energy in small, manageable amounts, so little is wasted as heat
• hydrolysis is a single, quick step
• it is soluble and moves easily within the cell
• it is regenerated rapidly, so a small store is enoughCells use ATP for muscle contraction, active transport, synthesis of macromolecules and nerve impulse transmission.Worked example: a cell hydrolyses 2 mol of ATP. Energy released = 2 × 30.5 = 61 kJ.
ATP is remade from ADP and Pi by ATP synthase in a condensation reaction, using energy from respiration (and from light in photosynthesis).ATP suits its role because:• it releases energy in small, manageable amounts, so little is wasted as heat
• hydrolysis is a single, quick step
• it is soluble and moves easily within the cell
• it is regenerated rapidly, so a small store is enoughCells use ATP for muscle contraction, active transport, synthesis of macromolecules and nerve impulse transmission.Worked example: a cell hydrolyses 2 mol of ATP. Energy released = 2 × 30.5 = 61 kJ.