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Adenosine triphosphate ( ATP) is a nucleotide consisting of the triphosphate of the nucleoside adenosine ( and as such a high-energy component of the nucleic acid is RNA ).
However, ATP is mainly the universal and immediately available energy in each cell and also an important regulator of energy -supplying processes. The ATP molecule consists of an adenine, the sugar ribose and three phosphates ( α and γ ) in the ester ( α ) or anhydride ( β and γ ).
- 4.1 Short-term regeneration in muscle cells
- 4.2 Other forms of energy production in muscle cells
- 4.3 provision of energy in the heart muscle
ATP was discovered in 1929 by the German biochemist Karl Lohmann. A chemical synthesis of ATP was first published in 1949 by James Alexander Robertus Todd and Baddiley. The role as the main source of energy in cells 1939 and 1941 by Fritz Lipmann enlightened after Vladimir Alexandrovich Engelhardt already had shown in 1935 that ATP is necessary for muscle contractions, and Herman Kalckar in 1937 the formation of ATP synthase with the respiratory chain found. The first involved in the synthesis of ATP enzymes were determined by Efraim Racker 1961.
Importance of ATP as an energy source for the organism
For running processes in cells energy is needed in order to thus make chemical, osmotic or mechanical work. This energy must be provided. This is done by the molecule ATP. The phosphates are interconnected by phosphoanhydride bonds ( acid anhydride bonds). These bonds cleaved hydrolytically by enzymes, there arises the adenosine diphosphate ( ADP) and orthophosphate or adenosine monophosphate ( AMP) and pyrophosphate. The cleavage of the bond first of all used as any bond cleavage energy. Overall, however, are by the subsequent hydration of the cleaved phosphate under standard conditions, respectively 32.3 kJ / mol ( bond cleavage ) or 64.6 kJ / mol (cleavage of both bonds) energy for work performed in the cell -free.
As an energy source, ATP is used for the basic energy-consuming processes of all living organisms: chemical, such as synthesis of organic molecules, osmotic work, such as active mass transport through biological membranes and into the cells, or addition, and mechanical operations, such as movements, for example in muscle contraction.
ATP as a signaling molecule
ATP is a co-substrate of the kinases, a group of phosphate -transferring enzymes play in metabolism and in the regulation of metabolism a key role. Significant members of the latter group are the protein kinases which, depending on their activation mechanism as protein kinase A (PKA, cAMP - dependent), protein kinase C (PKC, calcium - dependent), calmodulin -dependent kinase, or insulin -stimulated protein kinase ( ISPK ) referred to, to name but a few. Lower blood sugar a few basic principles are addressed, according to which a series of kinases can be connected together to form an enzyme cascade.
ATP (as well as ADP and adenosine ) is an agonist of purinergic receptors that play in both the central and the peripheral nervous system play a role. Thus, it is involved in processes such as blood flow regulation or mediation of inflammatory responses. It will be distributed according to neural injury and can stimulate the proliferation of astrocytes and neurons.
Regeneration of ATP
From the AMP or ADP formed in the release of energy from ATP, the cell regenerates ATP. There are two different principles, as the substrate chain and Elektronentransportphosphorylierung ( respiratory chain ), respectively.
In the substrate chain a phosphate residue is bound to an intermediate product of the degradation of material and energy sources transmitted after further conversion of the intermediate to ADP.
In Elektronentransportphosphorylierung protons are transported through the membrane of an enclosed space of the cell to another through a transport of electrons along a redox gradient via different electron and hydrogen carriers in a membrane. In bacteria, as protons are pumped out. In eukaryotes, these processes take place in the mitochondria. There protons are exported to the intermembrane space of the matrix of the mitochondrion. In both cases, an electro-chemical difference is generated that is composed of a proton concentration difference and an electric potential difference. The backflow of protons through the membrane is also localized in the enzyme ATP synthase drives the reaction catalyzed by this enzyme energy-consuming binding of inorganic phosphate groups to ADP. In some organisms, sodium ions are used instead of protons, they have analog via a Na -dependent ATP synthase.
In chemotrophic organism, the electrons are injected in the form of the reducing agent NADH, NADPH, FADH2 or reduced ferredoxin in the respiratory chain. These originate from the oxidative degradation of high-energy compounds such as carbohydrates or fatty acids. The electrons are transferred in aerobic organisms, oxygen and causes water. In the anaerobic respiration of other electron may be used, such as sulfur or iron (II). In both cases, an electrochemical difference, which is used for formation of ATP. In eukaryotes is the process in the mitochondria, in prokaryotes place in the cytoplasm.
In phototrophic organisms are discharged at a high energy level by absorption of light by chlorophylls of these electrons. The light energy is used in order to produce an electro-chemical differences. In green plants, this takes place in the chloroplasts, rather than in bacteria in the cytoplasm. Because of the use of light one speaks in this case of photophosphorylation.
Short-term regeneration in muscle cells
Since the oxidative phosphorylation in the respiratory chain is a relatively slow process, the ATP supply must be replenished at short notice in highly stressed cells ( muscle cells). The ATP stock ( in the muscle cell about 6 mmol / kg muscle) extends at maximum contraction only about 2-3 seconds. A reserve provide here molecules with higher group transfer potential than ATP dar. mammalian muscle cells maintain a supply of creatine phosphate ( 21 mmol / kg muscle; 0.08 % per body weight) ready. Creatine kinase catalyzes the transfer of the phosphoryl group from creatine phosphate to ADP. Is this stock consumed after 6-10 seconds, the above mechanisms have to bear the ATP regeneration alone.
Other forms of energy production in muscle cells
While strong muscle stress muscle build glucose to lactate in lactic acid fermentation from to quickly generate ATP. Lactate itself is rebuilt in the liver to pyruvate and then glucose consumption of ATP ( gluconeogenesis ). This glucose is then made available to the muscle as an energy source. This cycle is also referred to as the Cori cycle.
In an emergency, also endogenous proteins are broken down to produce energy. Proteins are broken down into amino acids, and they are usually degraded to pyruvate. In the Cori cycle similar path pyruvate is first transamination to alanine and transported to the liver. There, these steps are reversed and the liver produces glucose from pyruvate again, which is the muscle provided. This cycle is also referred to as glucose -alanine cycle.
Energy supply to the heart muscle
The heart muscle using fatty acids as a fuel, these will be degraded in the β - oxidation in the numerous mitochondria. Furthermore, also glucose, lactate are degraded (via reoxidation to pyruvate ), ketone bodies and glycogen. At a high loading up to 60 % of the energy can be obtained from the oxidation of lactate.
In the cell, the ATP concentration is a control variable:
- Fall below a threshold value ( 4-5 mmol / L ) is activated energizing reactions (see phosphofructokinase );
- Exceeds the threshold causes the energy storage, for example by Formation of creatine phosphate as readily available (ATP -supplying ) storage in the muscle;
- Construction of glycogen as "energy cushion" in the liver. Carbohydrate and protein stores, however, are limited; Another energy surplus leads ( via acetyl -CoA) to store fat.
For an average adult human, the amount ATP, which is degraded daily in his body on and on, about his body mass. So an 80 -kg man consumes about 40 kg ATP per day ( equivalent to about 78.8 mol or 1025 molecules), which are replaced by newly formed another 40 kg. The ATP throughput may increase with intensive work on 0.5 kg per minute.