If we paraphrase 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, ranging from giant organisms such as the blue whale or the American sequoia, to ultramicroscopic bacteria, draw their supplies?
Biochemistry has found the answer to this question. Adenosine triphosphoric acid is a universal substance used by all the inhabitants of our planet. In this article, we will consider the structure and functions of ATP in various groups of living organisms. In addition, we will determine which organelles are responsible for its synthesis in plant and animal cells.
Discovery history
At the beginning of the 20th century, in the laboratory of Harvard Medical School, several scientists, namely Subbaris, Loman and Friske, discovered a compound close in structure to adenylribonucleic acid nucleotide. However, it contained not one, but as many as three phosphate acid residues connected to the monosaccharide ribose. Two decades later, F. Lipman, studying the functions of ATP, confirmed the scientific assumption that this compound carries energy. From that moment on, biochemists had a great opportunity to get acquainted in detail with the complex mechanism of the synthesis of this substance that occurs in the cell. Later, a key compound was discovered: an enzyme - ATP synthase, which is responsible for the formation of acid molecules in mitochondria. To determine what function ATP performs, let's find out what processes occurring in living organisms cannot be carried out without the participation of this substance.
Forms of existence of energy in biological systems
Diverse reactions occurring in living organisms require different types of energy that can transform into each other. These include mechanical processes (movement of bacteria and protozoa, contraction of myofibrils in muscle tissue), 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 is also a type of energy produced by living bodies.
All the above phenomena occurring in biological systems are impossible without ATP molecules, whose functions are to storeenergy in the form of macroergic bonds. They occur between the adenyl nucleoside and the 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 the macromolecules of organic compounds are exposed to the action of enzymes. Part of the received energy is dissipated in the form of heat or is used to maintain the optimal temperature of the internal contents of the cell. The remaining portion is accumulated in the form in mitochondria - the power stations of the cell. 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
An elementary unit of living matter - a cell, can only function if the energy is constantly updated in its life cycle. To fulfill this condition in cellular metabolism, there is a direction called dissimilation, catabolism or energy metabolism. In its oxygen-free stage, which is the simplest way to form and store energy, from each glucose molecule, in the absence of oxygen, 2 molecules of an energy-intensive substance are synthesized, which provides the main functions of ATP in the cell - supplying it with energy. Most reactions of the anoxic step occur in the cytoplasm.
Depending on the structure of the cell, it can proceed in various ways, for example, in the form of glycolysis, alcohol or lactic acid fermentation. However, the biochemical features 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 to a nitrate base - adenine, and a monosaccharide - ribose. Since almost all reactions in the cytoplasm of the cell are carried out in an aqueous medium, acid molecules, under the action of hydrolytic enzymes, break covalent bonds to form first adenosine diphosphoric acid, and then AMP. The reverse reactions leading to the synthesis of adenosine triphosphoric acid occur in the presence of the enzyme phosphotransferase. Since ATP performs the function of a universal source of cellular vital activity, it includes two macroergic bonds. With a successive rupture of each of them, 42 kJ is released. This resource is used in cell metabolism, in its growth and reproductive processes.
Value of ATP synthase
In organelles of general importance - mitochondria, located in plant and animal cells, there is an enzymatic system - the respiratory chain. It contains the enzyme ATP synthase. The biocatalyst molecules, which have the form of a hexamer consisting of protein globules, are immersed both in the membrane and instroma of mitochondria. Due to the activity of the enzyme, the energy substance of the cell is synthesized from ADP and residues of inorganic phosphate acid. The formed ATP molecules perform the function of accumulating the energy necessary for its vital activity. A distinctive feature of the biocatalyst is that when there is an excessive concentration of energy compounds, it behaves like a hydrolytic enzyme, splitting their molecules.
Features of the synthesis of adenosine triphosphoric acid
Plants have a serious metabolic feature that radically 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 organelles - chloroplasts. The enzyme ATP synthase already known to us is part of their thylakoids and stroma of chloroplasts. 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 have formed a perfect mechanism for the synthesis of such a compound as ATP, the functions of which are to provide the cell with energy.
