5.2  ATP: Energy for Cells

ATP (adenosine triphosphate) is the energy currency of cells, or in other words, it is the useable form of energy.

ATP is used to drive nearly all cellular activities. When a cell needs to perform a reaction that requires energy, it will break down a molecule of ATP. When ATP is broken apart, its stored energy is released. ATP are like the cell's batteries that are drained one at a time when the cell needs to perform a chemical reaction- like building a protein or moving its flagella in order to swim.

Structure of ATP

ATP is a nucleotide, similar to the monomers of DNA and RNA.

The ATP molecule contains three phosphate groups (DNA and RNA contain only 1 phosphate).

The energy of ATP is stored in the bonds between the phosphate groups.



ATP structure

Use and Production of ATP

The continual breakdown and regeneration of ATP is the ATP cycle. When ATP is broken apart, energy is released and we are left with ADP (which has 2 phosphates and P which is a single disconnected phosphate group). Think of ATP like a charged battery and ADP and phosphate like the 2 parts of a discharged (dead) battery.


The ATP cycle


Because of its instability, ATP provides only short term storage of energy. 

Carbohydrates and fats are high energy storage molecules that, when "burned", are used to generate ATP. Cells need a supply of these molecules so they can be burned to make enough ATP to keep the cell alive. Proteins can be used under certain circumstances.



The production of ATP has several benefits for cells.

ATP can be used for many different types of chemical reactions.

When ATP is split to release energy, the amount of energy released is sufficient for most reactions without being wasteful.

The breakdown of ATP can be coupled to energy-requiring reactions. 

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ATP has potential energy.




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