Adenosine triphosphate, commonly known as ATP, is a molecule that supplies energy within cells. It is the primary energy currency of the cell and is a product of processes like photophosphorylation (the addition of a phosphate group to a molecule using light energy), cellular respiration, and fermentation. All living organisms use ATP. In addition to serving as an energy source, ATP is also involved in signal transduction pathways for cellular communication and is incorporated into deoxyribonucleic acid (DNA) during DNA synthesis.
Structure of ATP
ATP is composed of the molecule adenosine (which is made up of adenine and ribose) and three phosphate groups. It is water-soluble and contains a high amount of energy due to the two phosphoanhydride bonds that connect the three phosphate groups.
Functions of ATP
Energy Source
ATP is the main energy carrier used for all cellular activities. When ATP is hydrolyzed and converted to adenosine diphosphate (ADP), energy is released. The removal of a phosphate group releases 7.3 kilocalories per mole, or 30.6 kilojoules per mole, under standard conditions. This energy drives all the reactions that take place within the cell. ADP can also be converted back into ATP so that energy is available for other cellular reactions.
ATP is produced through different methods:
- Photophosphorylation: A method specific to plants and cyanobacteria, it creates ATP from ADP using light energy and occurs during photosynthesis.
- Cellular Respiration: ATP is also formed through cellular respiration in the mitochondria. This can be via aerobic respiration, which requires oxygen, or anaerobic respiration, which does not. Aerobic respiration produces ATP (along with carbon dioxide and water) from glucose and oxygen. Anaerobic respiration uses chemicals other than oxygen and is primarily utilized by archaea and bacteria that live in anaerobic environments.
- Fermentation: Another way to produce ATP without oxygen; it is different from anaerobic respiration because it does not use an electron transport chain. Yeast and bacteria are examples of organisms that use fermentation to generate ATP.
Signal Transduction
ATP is a signaling molecule used for cellular communication. Kinases, enzymes that phosphorylate molecules, use ATP as a source of phosphate groups. Kinases are important for signal transduction, which is how a physical or chemical signal is transmitted from receptors on the cell’s exterior to the cell’s interior. Once the signal is inside the cell, the cell can respond appropriately. Cells may receive signals to grow, metabolize, differentiate into specific types, or even die.
DNA Synthesis
The nitrogenous base adenine is part of adenosine, a molecule that forms from ATP and is directly placed into RNA. The other nucleobases in RNA, cytosine, guanine, and uracil, are similarly formed from CTP, GTP, and UTP. Adenine is also found in DNA, and its incorporation is very similar, except that ATP is converted to deoxyadenosine triphosphate (dATP) before becoming part of a DNA strand.
ATP, ADP, AMP, cAMP
ADP (Adenosine Diphosphate)
Adenosine diphosphate (ADP), sometimes known as adenosine pyrophosphate (APP), especially in chemistry, has been mentioned earlier. It differs from ATP because it has two phosphate groups. ATP converts to ADP with the loss of a phosphate group, releasing energy. ADP itself is formed from AMP. The cycle between ADP and ATP during cellular respiration provides cells with the energy needed for cellular activities.
AMP (Adenosine Monophosphate)
Adenosine monophosphate (AMP), also known as 5′-adenylic acid, has only one phosphate group. This molecule is found in RNA and contains adenine, which is part of the genetic code. It can be produced along with ATP from two molecules of ADP or by hydrolysis of ATP. It is also formed when RNA breaks down. AMP can convert into uric acid, which is a component of urine, and is excreted through the bladder.
cAMP (Cyclic Adenosine Monophosphate)
Cyclic adenosine monophosphate (cAMP) is derived from ATP and is another messenger used for signal transduction and the activation of certain protein kinases. It can be broken down into AMP. cAMP pathways can play a role in certain cancers, such as carcinoma. In bacteria, it has a role in their metabolism. When a bacterial cell does not produce enough energy (due to insufficient glucose, for example), elevated levels of cAMP are produced, activating genes that use energy sources other than glucose.
Related Biology Terms to Adenosine Triphosphate
- Cellular Respiration: The process by which energy from nutrients is converted into ATP.
- Signal Transduction: The transmission of signals from outside to inside a cell.
- Hydrolysis: The breaking of a bond in a molecule using a reaction with water.
- Kinase: An enzyme that transfers a phosphate group from ATP to another molecule.