What is the ATP in Biology?

ATP cycle and oxidative phosphorylation

We explain what ATP is, what it is for and how this molecule is produced. In addition, what is the ATP cycle and oxidative phosphorylation.

  1. What is the ATP?

In biochemistry , the acronym ATP designates Adenosine Triphosphate or Adenosine Triphosphate, an organic molecule of the nucleotide type , essential for obtaining chemical energy . ATP is the main source of energy for most cell processes and functions of the human body and other living things .

The name of ATP comes from the molecular composition of this coenzyme, from a nitrogenous base (known as adenine) bonded with the carbon atom of a pentose sugar molecule (also called ribose) and in turn with three phosphate ions bonded in Another carbon atom. All this is summarized in the molecular formula of C10H16N5O13P3 .

The ATP molecule was discovered by the German biochemist Karl Lohmann in 1929 , and its functioning and importance in the different energy transfer processes of the cell were recorded only in 1941, thanks to the studies of the German-American biochemist Fritz Albert Lipmann .

  1. What is the ATP for?

ATP is a useful molecule to momentarily contain the chemical energy released during the metabolic processes of food breakdown , and release it again when necessary to boost the body’s various biological processes , such as cell transport, promote energy- consuming reactions or even to perform mechanical actions of the body, such as walking.

It must be said that ATP does not serve to store chemical energy, as occurs with glucoses or fat; It serves as a transport to the cellular regions where it is needed . Thus, when an energy injection is required, ATP is generated and undone as needed, since it is very soluble in water , through the process known as hydrolysis , and when dissolved releases a large amount of energy in the form of phosphates and Other useful molecules.

  1. How is ATP produced?

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

ATP is synthesized through cellular respiration , specifically through the Krebs cycle, which is carried out in the mitochondria of the cell. For this, chemical energy stored in glucose, proteins and fats is released, through an oxidation process that releases CO2 and energy in the form of ATP. Each of these nutrients from the individual’s diet has 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 The cells consume their energy in the form of ATP.

As said before, ATP cannot be stored in its natural state , but as part of more complex compounds, such as glycogen (where glucose is obtained and oxidation of this, in turn, ATP) in animals or Starch in plants . Similarly, it can be stored in the form of animal fat, through the synthesis of fatty acids.

  1. ATP cycle

The ATP Cycle involves various stages of chemical transformation, the most important being known as the Krebs Cycle (also the Citric Acid Cycle or the Tricarboxylic Acid Cycle). It is a fundamental process that occurs in the matrix of cellular mitochondria , and that consists of a succession of chemical reactions that aims to release the chemical energy contained in Acetyl-CoA obtained from the processing of the different nutritional nutrients of being alive, as well as obtaining precursors of other amino acids necessary for other biochemical reactions.

This cycle is part of a much larger process that is the oxidation of carbohydrates, lipids and proteins , being its intermediate stage: after the formation of Acetyl-CoA with the carbons of these organic compounds, and prior to oxidative phosphorylation where the “ATP” is assembled by an enzyme called ATP synthetase.

The Krebs Cycle operates thanks to 8 different enzymes that completely oxidize Acetyl-CoA and release two different molecules from each oxidized molecule: CO2 (carbon dioxide) and H2O (water). This occurs when the Acetyl-CoA is removed from carbon atoms that come together with oxaloacetate to form citrate or citric acid (with six carbons), which in turn undergoes a series of transformations that will successively cause isocitrate, ketoglutarate, succinyl-CoA, succinate, fumarate, malate and oxaloacetate again, producing on the way the material from which various ATP molecules will then be obtained.

  1. Oxidative phosphorylation

ATP - Oxidative Phosphorylation
The NADH and FADH2 molecules are able to donate electrons in the Krebs cycle. 

This is the last stage of the nutrient utilization circuit (catabolism) that results in the production of ATP. It occurs in the cells and is the closure of cellular respiration, after glycolysis and the Krebs cycle. In it, about 38 ATP glucose are obtained for each glucose molecule, thanks to the NADH and FADH2 molecules that during the Krebs cycle were “charged” and can donate electrons .

This process operates based on two opposing reactions : one that releases energy and another that uses that energy released to produce ATP molecules, thanks to the intervention of ATP Sintetase, the enzyme responsible for building energy molecules, adding protons and a phosphate molecule to an ADP molecule (adenosine diphosphate), to obtain water and ATP.

  1. Importance of ATP

ATP is a fundamental molecule for the vital processes of living organisms, as a transmitter of chemical energy for the synthesis of complex and fundamental macromolecules , such as those of DNA , RNA or for the synthesis of proteins that occur within the cell. That is, the ATP provides a necessary energy load for certain reactions that take place in the body.

This is explained because it has energy-rich bonds, which can be dissolved in water by the following reaction:

ATP + H2O = ADP (Adenosine Diphosphate) + P + Energy

ATP is key for the transport of macromolecules through the plasma membrane (exocytosis and cell endocytosis) and also for synaptic communication between neurons , so its continuous synthesis is essential, from glucose obtained from the food. Such is its importance for life, that the intake of some toxic elements that inhibit ATP processes, such as arsenic or cyanide, is lethal and causes death in a fulminating way.

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