Adenosine triphosphate
- For other uses of the initials ATP, see ATP (disambiguation)
Adenosine triphosphate (ATP) is the nucleotide known in biochemistry as the "molecular currency" of intracellular energy transfer; that is, ATP is able to store and transport chemical energy within cells. ATP also plays an important role in the synthesis of nucleic acids.
Chemical properties
Chemically, ATP consists of adenosine and three phosphate groups. It has the empirical formula C10H16N5O13P3, and the chemical formula C10H8N4O2NH2(OH)2(PO3H)3H, with a molecular mass of 507.184 u.
Functions
ATP molecules are used to store the energy plants make in cellular respiration.
Phosphoryl positions
The phosphoryl groups starting with that on AMP are referred to as the alpha, beta, and gamma phosphates.
Synthesis
ATP can be produced by various cellular processes, most typically in mitochondria by oxidative phosphorylation under the catalytic influence of ATP synthase or in the case of plants in chloroplasts by photosynthesis.
The main fuels for ATP synthesis are glucose and fatty acids. Initially glucose is broken down into pyruvate in the cytosol. Two molecules of ATP are generated for each molecule of glucose. The terminal stages of ATP synthesis are carried out in the mitochondrion and can generate up to 36 ATP.
ATP in the human body
The total quantity of ATP in the human body is about 0.1 mole. The energy is used by human cells for the hydrolysis of 200 to 300 moles of ATP daily. This means that each ATP molecule is recycled 2000 to 3000 times during a single day. ATP cannot be stored, hence its synthesis must closely follow its consumption.
Human ATP synthesis
The body has four methods to create ATP, they vary by speed, and by whether they burn oxygen or not.
- Explosive Force - The ATP-CP System: ADP + Creatine phosphate (CP) ==> ATP + Creatine. By far the fastest way to get that third phosphate group is to grab it off of a molecule called "creatine phosphate" or CP. When you are doing very explosive exercise for 10-30 seconds, such as an all-out sprint, the burst of energy is delivered by the ATP-CP system. Fast, doesn't require oxygen, but extremely limited to short periods of explosive force.
- Sugar Burning - Step 1 (Anaerobic Glycolysis): ADP + glucose ==> ATP + pyruvic acid (which converts to lactate if not burned with oxygen). The next fastest method of getting energy is to turn a sugar molecule into lactic acid. This doesn't require oxygen either. This system is effective for vigorous exercise of between 1-3 minutes in duration. When the intensity of the exercise requires more energy than what can be burned with the oxygen you are breathing, your body starts "partially" burning glucose anaerobically (without oxygen). This is the system you want to be using during "wind sprints". This is a system that has to be trained in order to get fast results, but again, this system can be used only for a limited period. As lactic acid builds up in your muscles, you start to feel them "burn". If you go beyond a few minutes of this, the acidity of the muscle tissue increases and the muscles start to have difficulty generating meaningful amounts of energy.
- Sugar Burning - Step 2 (Aerobic Glycolysis): ADP + lactate + oxygen ==> ATP + water + carbon dioxide. This is the next system, and for all practical purposes is the one you use most often when exercising. Once glucose has been converted to lactate anaerobically (without oxygen), the body then burns the lactate using oxygen to create more ATP.
- Fat Burning (Aerobic Lipolysis): Fat + oxygen + ADP ==> ATP + water + carbon dioxide. This is by far the slowest system. It is, in fact, too slow to contribute extensively to energy production during exercise (in fact, if you ever deplete your glycogen stores so much that the body has to rely on lipolysis for its energy, your muscle movement slows down dramatically). In order to mobilize fat, a "triglyceride" has to be broken down into fatty acids, bound to proteins, and other time-consuming feats. The good news, is that lipid (fat) metabolism is the main way that your glycogen stores are replenished after exercise. That's why it can be useful to work out in the morning on an empty stomach and wait about an hour after your workout before eating - your glycogen stores are more depleted by the end of your workout and you burn more fat afterward.
Other triphosphates
Living cells also have other "high-energy" nucleoside triphosphates, such as guanine triphosphate. Between them and ATP, energy can be easily transferred with reactions such as those catalyzed by nucleoside diphosphokinase: Energy is released when hydrolysis of the phosphate-phosphate bonds is carried out. This energy can be used by a variety of enzymes, motor proteins, and transport proteins to carry out the work of the cell. Also, the hydrolysis yields free inorganic phosphate and adenosine diphosphate, which can be broken down further to another phosphate ion and adenosine monophosphate. ATP can also be broken down to adenosine monophosphate directly, with the formation of pyrophosphate. This last reaction has the advantage of being an effectively irreversible process in aqueous solution.
Reaction of ADP with GTP
There is talk of using ATP as a power source for nanotechnology and implants. Artificial pacemakers could become independent of batteries.
See also
- Adenosine diphosphate (ADP)
- Adenosine monophosphate (AMP)
- ATPases
- ATP Hydrolysis
- Citric acid cycle (also called the Krebs cycle)
- Cyclic adenosine monophosphate (cAMP)
- Phosphagen
- Thioesters are related to ATP
External link
- ATP and biological energy (http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookATP.html)
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