science

1. HB 3.A.1 ATP and ADP Cycle
Develop and use models to explain
how chemical reactions among ATP,
ADP and inorganic phosphate act to
transfer chemical energy within cells

2. What are ATP and ADP?
• ATP- adenosine triphosphate supplies energy
to the cell
– the most important biological molecule
• ATP is composed of three parts
1. A nitrogenous base (adenine)
2. A sugar (ribose)
3. Three phosphate groups bonded by “high energy
bonds”
• ADP is adenosine diphosphate and is the
spent molecule of ATP
– Has two phosphate groups and a lot less energy

5. ATP-ADP Cycle
• Cells break phosphate bonds to supply energy
to carry out most cellular functions converting
ATP into ADP and a phosphate available for
reuse
– When any phosphate bonds are broken, or formed
energy is involved
• When a phosphate is removed from ATP energy is
released
• Energy is used when a phosphate bonds to the molecule
• ADP is recycled back into ATP
– Because ADP has less energy than ATP

6. The ATP – ADP cycle

7. The steps to the ATP-ADP cycle
• ATP is broken to supply cells with high amounts
of energy
• ADP is formed and released back into the
cytoplasm
ATP  ADP + phosphate group + energy
• When the cell needs more energy a phosphate
attaches to ADP to form ATP the energy used
to attach the free phosphate is about the same
as energy given off by the breaking of the
phosphate bond in ATP
ADP + phosphate + energy  ATP