Adenosine triphosphate, also known as ATP, is the energy molecule of all living cells. When plants get energy from sunlight and animals get energy from food, this energy must be converted to ATP before it can be used by the cells to carry out all necessary functions.
Structure of ATP
ATP is made of an adenine nucleotide (an adenine base plus a ribose sugar) with three phosphates attached to it. Nucleotides are sugar and base molecules, and they are the same kinds of molecules that make up DNA. The "A" in ATP is the same "A" that can be found in the genetic code. In ATP, however, it has those three important phosphates, all lined up in a row and attached to the sugar (ribose) side of the nucleotide.
ATP Releases Energy to Power the Cell
The key to the energy-generating activity of adenosine triphosphate is the chain of three phosphates at the end of the molecule. In particular, the final phosphate is the most important one.
When an enzyme in the cell tells ATP to release energy, that final phosphate breaks off of the molecule. This breakage causes a huge amount of energy to be generated, which the cell can then use. This leaves a molecule of ADP, adenosine diphosphate, which can then lose another phosphate to release even more energy or can return to the ribosomes to have another phosphate put back on and return it to ATP status.
How Adenosine Triphosphate is Formed
When Adenosine Diphosphate, ADP, a molecule like ATP but with only two phosphates instead of three, visits the mitochondria or chloroplasts, it can be made into ATP. The mitochondria or chloroplast uses energy from food or sunlight to attach a third phosphate group onto the ADP. This reaction can also take place in the cytosol, the liquid of the cell, under some conditions.
Where Adenosine Triphosphate Energy is Used in the Cell
The energy produced by the transformation of ATP into ADP is used in many places in the cell. Muscles use ATP energy to contract, cilia and flagella use ATP to move, neurons use this energy to send nerve signals along synapses and it is even used in bioluminescence by some organisms.
Other Functions of ATP
Aside from acting as the energy carrier of all living cells, ATP also performs many other functions. In some cases, it can be used as a substrate for other molecules to be built on it and adenosine triphosphate regulates many types of cell activity by controlling and affecting biochemical pathways that operate in the cell. When it donates a phosphate group to some molecules, this can change the activity of that cell component or alter the signal it sends to other places in and out of the cell, affecting cell signaling. It also acts as a step in the formation of RNA, DNA and proteins.
Outside of the cell, ATP can act as a signaling molecule itself. An extracellular release of ATP in different areas of the body can signal pain, oxygen depletion and other biological needs.
All of these important functions are the result of the conversion of ATP into ADP, a cellular process that works 24 hours a day to keep organisms functioning and healthy. That's why adenosine triphosphate is often considered the most important molecule in living cells.
Bridget Coila - I'm a cell and molecular biologist, freelance writer and photographer currently living in Beijing, China. I'm fascinated by science, ...
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