We explain what ATP is, what it is for and how this molecule is produced. Also, glycolysis, Krebs cycle, and oxidative phosphorylation.

The ATP molecule was discovered by the German biochemist Karl Lohmann in 1929.

What is ATP?

In thebiochemistry, the acronym ATP designates Adenosine Triphosphate or Adenosine Triphosphate, an organic molecule belonging to the group of nucleotides, fundamental for the energy metabolism of the cell. ATP is the main source of energy used in most cellular processes and functions, both in the human body and in the body of beings.

The name of ATP comes from the molecular composition of this molecule, formed by a nitrogenous base (adenine) linked to theatom carbon onemolecule of pentose sugar (also called ribose), and in turn with threeions phosphates attached to another carbon atom. All of this is summarized in the molecular formula of ATP: C10H16N5O13P3.

The ATP molecule was first discovered in 1929 in human muscle in the United States by Cyrus H. Fiske and Yellapragada SubbaRow, and independently in Germany by the biochemist Karl Lohmann.

Although the ATP molecule was discovered in 1929, there was no record of its functioning and importance in the differentprocesses of energy transfer of the cell until 1941, thanks to the studies of the German-American biochemist Fritz Albert Lipmann (winner of the Nobel Prize in 1953, together with Krebs).

See also:Metabolism

What is ATP for?

The main function of ATP is to serve as an energy supply in the biochemical reactions that take place inside the cell, which is why this molecule is also known as the organism's “energy currency”.

ATP is a useful molecule to momentarily contain the chemical energy released during the metabolic processes of decomposition offood, and release it again when necessary to drive the various biological processes of the body, such as cell transport, promote reactions that consumeEnergy or even to carry out mechanical actions of the body, such as walking.

How is ATP made?

To synthesize ATP it is necessary to release chemical energy stored in glucose.

In cells, ATP is synthesized through cellular respiration, a process that takes place in cells.mitochondria of the cell. During this phenomenon, the chemical energy stored in glucose is released, through a process ofoxidation that releasesCO2, H2O and energy in the form of ATP. Although glucose is the substrate par excellence of this reaction, it should be clarified thatprotein and the fats they can also be oxidized to ATP. Each of these nutrients from the feeding of the individual have different metabolic pathways, but they converge on a common metabolite: acetyl-CoA, which starts the Krebs Cycle and allows the process of obtaining chemical energy to converge, since all cells consume their energy in the form of ATP .

The cellular respiration process can be divided into three phases or stages: glycolysis (a prior pathway that is only required when the cell uses glucose as fuel), the Krebs cycle, and the electron transport chain. During the first two stages, acetyl-CoA, CO2 and only a small amount of ATP are produced, while during the third phase of respiration it is produced H2O and most of the ATP through a set of proteins called "complex ATP synthase".


As mentioned, glycolysis is a pathway prior to cellular respiration, during which for each glucose (which has 6 carbons) two pyruvates are formed (a compound formed by 3 carbons).

Unlike the other two stages of cellular respiration, glycolysis takes place in the cytoplasm of the cell. The pyruvate resulting from this first pathway must enter the mitochondria to continue its transformation into Acetyl-CoA and thus be able to be used in the Krebs cycle.

Krebs cycle

The Krebs Cycle is part of the oxidation process of carbohydrates, lipids and proteins.

The Krebs cycle (also citric acid cycle or tricarboxylic acid cycle) is a fundamental process that occurs in the matrix of cellular mitochondria, and that consists of a succession of chemical reactions what has likeobjective the release of the chemical energy contained in the Acetyl-CoA obtained from the processing of the different food nutrients of the living being, as well as the obtaining of precursors of other amino acids necessary for biochemical reactions of another nature.

This cycle is part of a much larger process that is the oxidation of carbohydrates, lipids and proteins, its intermediate stage being: after the formation of Acetyl-CoA with the carbons of said organic compounds, and prior to oxidative phosphorylation. where ATP is "assembled" in a reaction catalyzed by aenzyme called ATP synthetase or ATP synthase.

The Krebs Cycle operates thanks to several different enzymes that completely oxidize Acetyl-CoA and release two different ones from each oxidized molecule: CO2 (carbon dioxide) and H2O (water). In addition, during the Krebs cycle, a minimum amount of GTP (similar to ATP) is generated and reducing power in the form of NADH and FADH2 that will be used for the synthesis of ATP in the next stage of cellular respiration.

The cycle begins with the fusion of an acetyl-CoA molecule with an oxaloacetate molecule. This union gives rise to a six-carbon molecule: citrate. Thus, coenzyme A is released. In fact, it is reused many times. If there is too much ATP in the cell, this step is inhibited.

Subsequently, the citrate or citric acid undergoes a series of successive transformations that will successively originate isocitrate, ketoglutarate, succinyl-CoA, succinate, fumarate, malate and oxaloacetate again. Together with these products, a minimum amount of GTP is produced for each complete Krebs cycle, reducing power in the form of NADH and FADH2 and CO2.

Electron transport chain and oxidative phosphorylation

The NADH and FADH2 molecules are capable of donating electrons in the Krebs cycle.

The last stage of the nutrient harvesting circuit uses oxygen and compounds produced during the Krebs cycle to produce ATP in a process called oxidative phosphorylation. During this process, which takes place in the inner mitochondrial membrane, NADH and FADH2 donate electrons driving them to an energetically lower level. These electrons are finally accepted by oxygen (which when joining with protons gives rise to the formation of water molecules).

The coupling between the electronic chain and oxidative phosphorylation operates on the basis of two opposing reactions: one that releases energy and the other that uses that released energy to produce ATP molecules, thanks to the intervention of ATP synthetase. As the electrons "travel" down the chain in a series of redox reactions, the released energy is used to pump protons through the membrane. When these protons diffuse back through ATP synthetase, their energy is used to bind an additional phosphate group to an ADP (adenosine diphosphate) molecule, leading to the formation of ATP.

Importance of ATP

ATP is a fundamental molecule for the vital processes of living organisms, as a transmitter of chemical energy for different reactions that occur in the cell, for example, the synthesis of macromolecules complex and fundamental, such as those of theDNARNA or for protein synthesis that occurs within the cell. Thus, ATP provides the energy necessary to allow most of the reactions that take place in the body.

The usefulness of ATP as an “energy donor” molecule is explained by the presence of phosphate bonds, rich in energy. These same bonds can release a large amount of energy by “breaking” when ATP is hydrolyzed to ADP, that is, when it loses a phosphate group due to the action of water. Reaction of hydrolysis ATP is as follows:

ATP is essential, for example, for muscle contraction.

ATP is key for the transport of macromolecules through theplasma membrane (exocytosis and cellular endocytosis) and also for synaptic communication betweenneurons, so its continuous synthesis is essential, starting from glucose obtained from food. Such is its importance for the life, that the ingestion of some toxic elements that inhibit ATP processes, such as arsenic or cyanide, is lethal and causes the death of the organism in a fulminant way.

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