• H.B.3.A.1 Develop and use models to explain how
chemical reactions among ATP, ADP, and inorganic
phosphate act to transfer chemical energy within cells.
• B-3.3 Recognize the overall structure of adenosine
triphosphate (ATP)---namely, adenine, the sugar ribose,
and three phosphate groups ---and summarize its
function including the ATP-ADP [adenosine
ATP: The Cell’s Currency
Life processes require a constant supply of energy.
Cells use energy that is stored in the bonds of certain
Adenosine triphosphate (ATP) is a molecule that
transfers energy from the breakdown of food
molecules to cell processes.
Adenosine triphosphate (ATP) is the most important
biological molecule that supplies energy to the cell.
A molecule of ATP is composed of three parts bonded
together by “high energy” bonds:
1. A nitrogenous base (adenine)
2. • A sugar (ribose)
3. • Three phosphate groups (triphosphate)
Where does ATP come from?
ATP comes indirectly from the food that we eat.
Molecules of carbohydrates (glucose) and lipids are
broken down through the process of cellular
respiration to produce ATP.
The energy stored in ATP is released when a phosphate group is
removed from the molecule.
ATP has three phosphate groups, but the bond holding the third
phosphate groups is very easily broken.
When the phosphate is removed, ATP becomes ADP—
A phosphate is released into the cytoplasm and energy is
ADP is a lower energy molecule than ATP, but can be converted
to ATP by the addition of a phosphate group.
ATP → ADP + phosphate + energy available for cell processes
Steps in the ADP-ATP Cycle
To supply cells with energy, a “high energy” bond in
ATP is broken. ADP is formed and a phosphate is
released back into the cytoplasm.
ATP ADP + phosphate + energy
Steps in the ADP-ATP Cycle
As the cell requires more energy, ADP becomes
ATP when a free phosphate attaches to the ADP
molecule. Then energy needed to create an ATP
molecule is much less than the amount of energy
produced when the bond is broken.
ADP + phosphate + energy ATP
How do you “recharge” the battery?
ADP is continually converted to ATP by the addition of a
phosphate during the process of cellular respiration.
ATP carries much more energy than ADP.
As the cell requires more energy, it uses energy from the
breakdown of food molecules to attach a free phosphate
group to an ADP molecule in order to make ATP.
ADP + phosphate + energy from breakdown of food
When is ATP used?
ATP is consumed in the cell by energy-requiring
processes and can be generated by energy-releasing
In this way ATP transfers energy between separate
biochemical reactions in the cell.
ATP is the main energy source for the majority of cellular
This includes the production of organic molecules,
including DNA and, and proteins.
ATP also plays a critical role in the transport of organic
molecules across cell membranes, for example during
exocytosis and endocytosis
Types of Reactions
Ex. Cellular respiration
Endergonic (energy-requiring) reactions
ATP VS ADP
Main energy source for the cell Contains Less energy
Contains 3 phosphate groups
Contains 2 phosphate groups