If you rephrase the well-known expression “movement is life”, it becomes clear that all manifestations of living matter - growth, reproduction, processes of synthesis of nutrients, respiration - are, in fact, the movement of atoms and molecules that make up the cell. Are these processes possible without the participation of energy? Of course not.
Where do living bodies come from, from giant organisms, such as the blue whale or American sequoia, to ultramicroscopic bacteria?
Biochemistry has found the answer to this question. Adenosine triphosphoric acid is the universal substance used by all the inhabitants of our planet. In this article, we consider the structure and functions of ATP in various groups of living organisms. In addition, we determine which organelles are responsible for its synthesis in plant and animal cells.
Discovery story
At the beginning of the 20th century, several scientists, namely Subbaris, Loman and Friske, discovered a compound in the laboratory of Harvard Medical School that was close in structure to the adenyl nucleotide of ribonucleic acids. However, it did not contain one, but as many as three residues of phosphate acid combined with ribose monosaccharide. Two decades later, F. Lipman, studying the functions of ATP, confirmed the scientific assumption that this compound transfers energy. From that moment on, biochemists had a great opportunity to familiarize themselves in detail with the complex mechanism of synthesis of this substance that occurs in the cell. Subsequently, a key compound was discovered: the enzyme, ATP synthase, is responsible for the formation of acid molecules in mitochondria. To determine what function ATP performs, we find out what processes taking place in living organisms cannot be realized without the participation of this substance.
Forms of the existence of energy in biological systems
The diverse reactions that occur in living organisms require different types of energy that can transform into each other. These include mechanical processes (the movement of bacteria and protozoa, the contraction of myofibrils in muscle tissue), and biochemical synthesis. This list also includes electrical impulses that underlie excitation and inhibition, thermal reactions that maintain a constant body temperature in warm-blooded animals and humans. The luminescent glow of marine plankton, some insects and deep-sea fish also belongs to the types of energy produced by living bodies.
All the phenomena described above that occur in biological systems are impossible without ATP molecules, whose functions are to store energy in the form of macroergic bonds. They arise between adenyl nucleoside and phosphate acid residues.
Where does cellular energy come from?
According to the laws of thermodynamics, the appearance and disappearance of energy occurs for certain reasons. The breakdown of organic compounds that make up food: proteins, carbohydrates and especially lipids leads to the release of energy. The primary processes of hydrolysis occur in the digestive tract, where macromolecules of organic compounds are exposed to enzymes. Part of the energy received is dissipated in the form of heat or is used to maintain the optimum temperature of the internal contents of the cell. The remaining portion is accumulated in the form in mitochondria - cell power stations. This is the main function of the ATP molecule - providing and replenishing the energy needs of the body.
What is the role of catabolic reactions
The elementary unit of living matter - the cell, can function only under the condition of constant renewal of energy in its life cycle. To fulfill this condition, there is a direction in cellular metabolism called dissimilation, catabolism, or energy metabolism. In its oxygen-free stage, which is the easiest way to generate and store energy, from each glucose molecule, provided there is no oxygen, 2 molecules of an energy-intensive substance are synthesized that provide the main functions of ATP in the cell - supplying it with energy. Most reactions of the anoxic phase occur in the cytoplasm.
Depending on what the structure of the cell is, it can proceed in various ways, for example, in the form of glycolysis, alcoholic or lactic acid fermentation. However, the biochemical characteristics of these metabolic processes do not affect the function of ATP in the cell. It is universal: to preserve the energy reserves of the cell.
How the structure of a molecule is related to its functions
Earlier, we established the fact that adenosine triphosphoric acid contains three phosphate residues connected with a nitrate base - adenine, and a monosaccharide - ribose. Since almost all reactions in the cell cytoplasm are carried out in an aqueous medium, acid molecules under the action of hydrolytic enzymes break covalent bonds with the formation of adenosine diphosphoric acid, and then AMP. The reverse reactions leading to the synthesis of adenosine triphosphoric acid occur in the presence of the phosphotransferase enzyme. Since ATP serves as a universal source of cellular activity, it includes two macroergic bonds. With a sequential break of each of them, 42 kJ is released. This resource is used in the metabolism of cells, in its growth and reproductive processes.
The value of ATP synthases
In organelles of general importance - mitochondria located in plant and animal cells, there is an enzymatic system - the respiratory chain. It contains an enzyme - ATP synthase. Biocatalyst molecules having the form of a hexamer consisting of protein globules are immersed both in the membrane and in the stroma of the mitochondria. Due to the activity of the enzyme, the synthesis of the cell’s energetic substance occurs from ADP and residues of inorganic phosphate acid. The resulting ATP molecules perform the function of accumulating the energy necessary for its vital functions. A distinctive feature of the biocatalyst is that when the concentration of energy compounds is excessive, it behaves like a hydrolytic enzyme, breaking down their molecules.
Features of the synthesis of adenosine triphosphoric acid
Plants have a serious metabolic feature that fundamentally distinguishes these organisms from animals. It is associated with the autotrophic mode of nutrition and the ability to process photosynthesis. The formation of molecules containing macroergic bonds occurs in plants in cellular organoids - chloroplasts. The enzyme ATP synthase, already known to us, is part of thylakoids and stroma of chloroplasts in them. The functions of ATP in the cell are the storage of energy in both autotrophic and heterotrophic organisms, including humans.
Compounds with macroergic bonds are synthesized in saprotrophs and heterotrophs in oxidative phosphorylation reactions taking place on mitochondrial cristae. As you can see, in the process of evolution, various groups of living organisms formed a perfect synthesis mechanism for such a compound as ATP, whose functions are to provide cells with energy.