Adenosine triphosphate

The adenosine triphosphate (ATP) or adenosine triphosphate (TFA), (in English adenosine triphosphate), is a Fundamental nucleotide in obtaining cellular energy. It is formed by a nitrogenous base (adenine) attached to carbon one of a pentose sugar.

It is produced during photophosphorylation and cellular respiration, and is consumed by many enzymes in the catalysis of numerous chemical processes. Its molecular formula is C₁₀H₁₆N₅O₁₃P₃.

Discovery

Adenosine triphosphate was first found in human muscle in 1929 in the United States by Cyrus H. Fiske and Yellapragada Subbarao, and independently, in Germany by Karl Lohman.^{[citation needed]} However, it was not until ten years later that the central role of ATP in energy transfer began to be recognized. In 1941, Fritz Lipmann (Nobel Prize, 1953) helped by the contributions of Herman Kalckar, pointed out the hypothesis of the cyclical nature of the role of ATP in bioenergetic processes writing:

You cannot give definite answers to the question of how the high potential of the phosphate group operates as a promoter of several processes, but you can only recognize a more or less narrow interconnection with the replacement of the phosphate. The metabolic cycle is comparable to a machine that generates electric current. In fact, it seems that in the cellular organization, the "current" of phosphate plays a role similar to that of electric current in human life. And it is also a form of energy used for all purposes.

Chemical Properties

ATP is stable in aqueous solutions between pH 6.8 and 7.4, in the absence of catalysts. At more extreme pH, it is rapidly hydrolyzed to ADP and phosphate. Living cells maintain the ratio of ATP to ADP at a point ten orders of magnitude from equilibrium, with ATP concentrations five times the ADP concentration. In the context of biochemical reactions, P-O-P bonds are called frequently high-energy bonds.

Hydrolysis of ATP to ADP and inorganic phosphate releases 30.5 kJ/mol of enthalpy, with a change in free energy of 3.4 kJ/mol. The energy released by the splitting of a phosphate (Pi) or pyrophosphate unit (PPi) of ATP in the standard state of 1 M is:

ATP + H2O → ADP + P_i ΔG = −30.5 kJ/mol (−7.3 kcal/mol)

ATP + H2O → AMP + PP_i ΔG = −45.6 kJ/mol (−10.9 kcal/mol)

AMP and ADP production

ATP can be produced by several different cellular processes; The three main pathways in eukaryotes are (1) glycolysis, (2) the citric acid cycle/oxidative phosphorylation, and (3) beta-oxidation. The general process of oxidation of glucose to carbon dioxide, the combination of pathways 1 and 2, known as cellular respiration, produces approximately 30 equivalents of ATP from each glucose molecule. ATP production in a non-photosynthetic aerobic eukaryote occurs primarily in the mitochondria, which comprise nearly 25% of the volume of a typical cell.

Glycolysis

In glycolysis, glucose and glycerol are metabolized to pyruvate. Glycolysis generates two equivalents of ATP through substrate phosphorylation catalyzed by two enzymes, PGK and pyruvate kinase. Two equivalents of NADH are also produced, which can be oxidized through the electron transport chain and result in the generation of additional ATP by ATP synthase. The pyruvate generated as the end product of glycolysis is a substrate for the Krebs cycle. Glycolysis is considered to consist of two phases with five steps each. Phase 1, "the preparatory phase", glucose is converted to 2-d-glyceraldehyde-3-phosphate (g3p). One ATP is reversed in Step 1, and another ATP is reversed in Step 3. Steps 1 and 3 of glycolysis are called "Priming Steps." In Phase 2, the two g3p equivalents are converted to two pyruvates. In Step 7, two ATP are produced. Also, in Step 10, two more ATP equivalents are produced. In steps 7 and 10, ATP is generated from ADP. A two-ATP network is formed in the glycolysis cycle. The glycolysis pathway is later associated with the citric acid cycle which produces additional equivalents of ATP.

Krebs Cycle

In mitochondria, the pyruvate dehydrogenase complex oxidizes pyruvate to the acetyl group, which is fully oxidized to carbon dioxide by the citric acid cycle (also known as the Krebs cycle). Every "turn" of the citric acid cycle produces two molecules of carbon dioxide, one equivalent of guanosine triphosphate ATP (GTP) via substrate-level phosphorylation catalyzed by succinyl-CoA synthetase, as succinyl-CoA is converted to succinate, three equivalents of NADH and one equivalent of FADH2. NADH and FADH2 are recycled (to NAD+ and FAD, respectively), generating additional ATP by oxidative phosphorylation. The oxidation of NADH results in the synthesis of 2-3 equivalents of ATP, and the oxidation of a FADH2 produces between 1-2 equivalents of ATP. Most of the cellular ATP is generated by this process. Although the citric acid cycle itself does not involve molecular oxygen, it is a mandatory aerobic process because O2 is used to recycle NADH and FADH2. In the absence of oxygen, the citric acid cycle ceases.

In oxidative phosphorylation, the passage of electrons from NADH and FADH2 through the electron transport chain pumps protons out of the mitochondrial matrix and into the intermembrane space. This pumping generates a proton motive force that is the net effect of a pH gradient and an electrical potential gradient across the inner mitochondrial membrane. The flow of protons down this potential gradient, that is, from the intermembrane space to the matrix, produces ATP by ATP synthase. Three ATP are produced per turn. Although oxygen consumption appears critical for the maintenance of the proton motive force, in the event of oxygen starvation (hypoxia), intracellular acidosis (mediated by enhanced glycolytic rates and ATP hydrolysis), contributes to mitochondrial membrane potential and drives directly the synthesis of ATP.

Most of the ATP synthesized in the mitochondria will be used for cellular processes in the cytosol; therefore, it must be exported from its site of synthesis in the mitochondrial matrix. The outward movement of ATP is favored by the electrochemical potential of the membrane because the cytosol has a relatively positive charge compared to the relatively negative matrix. For each ATP carried, it costs 1 H+. One ATP costs about 3 H+. So making and exporting an ATP requires 4H+. The inner membrane contains an antiporter, the ADP/ATP translocase, which is an integral membrane protein used to exchange newly synthesized ATP in the matrix for ADP in the intermembrane space. This translocase is driven by membrane potential, as it results in the movement of approximately 4 negative charges out of the mitochondrial membrane in exchange for 3 negative charges moved in. However, it is also necessary to transport phosphate to the mitochondria; the phosphate carrier moves one proton with each phosphate, partially dissipating the proton gradient. After glycolysis, the citric acid cycle, the electron transport chain, and oxidative phosphorylation are complete, approximately 30-38 ATP are produced per glucose.

Beta oxidation

In the presence of air and various cofactors and enzymes, fatty acids are converted to acetyl-CoA. The pathway is called beta-oxidation. Each beta-oxidation cycle shortens the fatty acid chain by two carbon atoms and produces one equivalent each of acetyl-CoA, NADH, and FADH2. Acetyl-CoA is metabolized by the citric acid cycle to generate ATP, while NADH and FADH2 are used by oxidative phosphorylation to generate ATP. Tens of equivalents of ATP are generated by the beta-oxidation of a single long acyl chain.

Role in photosynthesis

Among the chemical reactions of plant photosynthesis, chlorophyll uses sunlight to drive a chain of reactions that stores energy, in the form of chemical energy, in the energetically charged molecule ATP. The chemical energy stored in the ATP is used by the plant in many chemical reactions when the plant needs energy to drive a reaction of this type, and many times the intake of ATP, which by giving it up is "spent" (becomes a lower energy molecule called ADP). The plant can use many molecules as a source of chemical energy (for example, it can use storage molecules, such as the starch of terrestrial plants, or transport molecules, sucrose), but many times, as a first step, the selected molecule to this must transfer its energy to ATP: through chemical reactions the molecule loses its chemical energy and in exchange ADP is charged with chemical energy in the form of ATP.

ATP training chemical reaction. The energy with which the ATP is formed can be taken for example from the light of the Sun, by photosynthesis, although it can also take energy by other means, such as the degradation of glucose.

Oxygen is not used from the products of photosynthesis and is released into the environment. From the products of photosynthesis, the chemical reactions of biosynthesis can be continued to build all the other molecules the plant needs (anabolism). Glucose and its derivatives are used by the plant in two ways: on the one hand, it uses them as structural components, with which the physical body of each plant cell is formed (in the form of cellulose); and on the other hand, it uses them as a source of chemical energy, for example to form more ATP when it is scarce. Although, during the process of photosynthesis, the plant takes some of the energy from sunlight to form ATP, it is not enough to cover its needs (especially at times when the plant is not exposed to light, and in organs that are not photosynthetic), so it must resort to glucose and other stored or transported derivatives to use them as a source of chemical energy, mainly in the process called cellular respiration, where plants also breathe oxygen.

Hydrolysis

ATP hydrolysis in ADP and phosphate

It can be represented as A-P~P~P, where °~°°~° are the acid anhydride bonds, which are of high energy. In the hydrolysis of ATP one of these acid anhydride bonds is being hydrolyzed. The formation of new bonds in hydrolysis allows the release of high energy, exactly 7.7 kcal/mol. That is to say:

ΔG = -7,7 kcal/mol or -31 KJ/mol approximately, which is the same.

It's a very exergenous reaction. His ${displaystyle k_{eq}}$ It's 11.

This is how it is understood that ATP has a tendency to hydrolyze naturally and release energy.

Chemical reasons for the tendency to hydrolysis

There are three chemical reasons for this trend:

1. Resonance stabilization energy: it is given by electronic delocalization, that is, because of the different electronivity between the P and the O, there is a displacement of the electrons from the double links to the O. In the double link they have a certain character of simple and vice versa.
   Resonance stabilization energy is higher in hydrolysis products than in ATP. This is mainly due to the fact that the electrons π (the red points in the O) of the oxygen bridge between the P are strongly attracted by the phosphoric groups.
   The competition for electrons π creates a tension in the molecule evidently lower (or is absent) in hydrolysis products. Therefore, there is greater resonance stabilization energy in hydrolysis products.
2. Electrical pressure between the neighboring negative loads in the ATP (arrows between the O of the Pi). This tension is evidently lower in hydrolysis products.
3. Solvation: the natural tendency is towards greater snuffing. Solvating energy is higher in hydrolysis products than in ATP.

There are many high-energy bonds in the cell, most of which are phosphate bonds. ATP occupies an intermediate position among the high-energy phosphates.

One of the most important functions of ATP is that it stores, in the form of chemical potential energy, a large amount of energy for biological functions, and it is released when one or two of the phosphates are separated from the ATP molecules.