Millions of biochemical reactions occur in any cell of our body. They are catalyzed by many enzymes, which often require energy. Where does the cell take it? This question can be answered if we consider the structure of the ATP molecule - one of the main sources of energy.
ATP - a universal source of energy
ATP stands for adenosine triphosphate, or adenosine triphosphoric acid. A substance is one of the two most important sources of energy in any cell. The structure of ATP and the biological role are closely related. Most biochemical reactions can occur only with the participation of molecules of the substance, especially with regard to plastic metabolism. However, ATP is rarely directly involved in the reaction: for any process to occur, energy is needed, which is precisely the chemical bonds of adenosine triphosphate.
The structure of the molecules of the substance is such that the bonds formed between the phosphate groups carry a huge amount of energy. Therefore, such relationships are also called macroergic, or macroenergetic (macro = a lot, a large number). The term macroergic relations was first introduced by the scientist F. Lipman, and he also proposed the use of the icon to denote them.
It is very important for the cell to maintain a constant level of adenosine triphosphate. This is especially characteristic of muscle tissue cells and nerve fibers, because they are the most energy-dependent and in order to perform their functions they need a high content of adenosine triphosphate.
ATP molecule structure
Adenosine triphosphate consists of three elements: ribose, adenine, and phosphoric acid residues.
Ribose is a carbohydrate that belongs to the group of pentoses. This means that in the composition of ribose there are 5 carbon atoms that are enclosed in a cycle. Ribose binds to the adenine β-N-glycosidic bond on the 1st carbon atom. Residues of phosphoric acid on the 5th carbon atom also join the pentose.
Adenine is a nitrogenous base. Depending on which nitrogenous base joins the ribose, GTP (guanosine triphosphate), TTF (thymidine triphosphate), CTF (cytidine triphosphate) and UTP (uridine triphosphate) are also secreted. All these substances are similar in structure to adenosine triphosphate and perform approximately the same functions, however, they are much less common in the cell.
Residues of phosphoric acid . A maximum of three phosphoric acid residues can join ribose. If there are two or only one, then, respectively, the substance is called ADP (diphosphate) or AMP (monophosphate). It is precisely between phosphorus residues that macro-energetic bonds are made, after the breaking of which 40 to 60 kJ of energy are released. If two bonds are broken, 80 are released, less often - 120 kJ of energy. When the bond between the ribose and the phosphorus residue is broken, only 13.8 kJ are released, therefore, there are only two macroergic bonds (P ̴ P ̴ P) in the triphosphate molecule, and one (P ̴ P) in the ADP molecule.
Here are the structural features of ATP. Due to the fact that a macroenergetic bond is formed between phosphoric acid residues, the structure and functions of ATP are interconnected.
The structure of ATP and the biological role of the molecule. Additional functions of adenosine triphosphate
In addition to energy, ATP can perform many other functions in the cell. Along with other nucleotide triphosphates, triphosphate is involved in the construction of nucleic acids. In this case, ATP, GTF, TTF, CTF and UTF are suppliers of nitrogen bases. This property is used in DNA replication and transcription processes.
ATP is also necessary for the operation of ion channels. For example, the Na-K channel pumps 3 sodium molecules out of the cell and pumps 2 potassium molecules into the cell. Such an ion current is needed to maintain a positive charge on the outer surface of the membrane, and only with the help of adenosine triphosphate can the channel function. The same applies to proton and calcium channels.
ATP is the precursor of the secondary messenger cAMP (cyclic adenosine monophosphate) - cAMP not only transmits the signal received by the cell membrane receptors, but is also an allosteric effector. Allosteric effectors are substances that accelerate or slow down enzymatic reactions. Thus, cyclic adenosine triphosphate inhibits the synthesis of an enzyme that catalyzes the breakdown of lactose in bacterial cells.
The adenosine triphosphate molecule itself can also be an allosteric effector. Moreover, ADF acts as an antagonist of ATP in such processes: if triphosphate accelerates the reaction, then diphosphate inhibits, and vice versa. These are the functions and structure of ATP.
How is ATP formed in a cell?
The functions and structure of ATP are such that the molecules of a substance are quickly used and destroyed. Therefore, the synthesis of triphosphate is an important process of energy formation in the cell.
Three most important methods for the synthesis of adenosine triphosphate are distinguished:
1. Substrate phosphorylation.
2. Oxidative phosphorylation.
3. Photophosphorylation.
Substrate phosphorylation is based on multiple reactions that occur in the cytoplasm of the cell. These reactions are called glycolysis - the anaerobic phase of aerobic respiration. As a result of 1 glycolysis cycle from 1 glucose molecule, two pyruvic acid molecules are synthesized , which are then used to generate energy, and two ATP are also synthesized.
- 6 12 6 + 2 + 2 ––> 2 3 4 O 3 + 2 + 4.
Oxidative phosphorylation. Cell breath
Oxidative phosphorylation is the formation of adenosine triphosphate by transferring electrons along the electron transport chain of the membrane. As a result of such a transfer, a proton gradient is formed on one of the sides of the membrane and molecules are being built using the protein integral kit of ATP synthase. The process takes place on the mitochondrial membrane.
The sequence of stages of glycolysis and oxidative phosphorylation in mitochondria is a general process called respiration. After a full cycle of 1 glucose molecule, 36 ATP molecules are formed in the cell.
Photophosphorylation
The process of photophosphorylation is the same oxidative phosphorylation with only one difference: photophosphorylation reactions occur in the chloroplasts of the cell under the influence of light. ATP is formed during the light phase of photosynthesis - the main process of generating energy in green plants, algae and some bacteria.
In the process of photosynthesis, electrons pass along the same electron transport chain, resulting in the formation of a proton gradient. The concentration of protons on one side of the membrane is a source of ATP synthesis. The assembly of molecules is carried out by the enzyme ATP synthase.
Interesting facts about ATP
- The average cell contains 0.04% of adenosine triphosphate from the entire mass. However, the greatest value is observed in muscle cells: 0.2-0.5%.
- There are about 1 billion ATP molecules in the cell.
- Each molecule lives no more than 1 minute.
- One adenosine triphosphate molecule is updated per day 2000-3000 times.
- In total, the human body synthesizes 40 kg of adenosine triphosphate per day, and at each point in time the supply of ATP is 250 g.
Conclusion
The structure of ATP and the biological role of its molecules are closely related. The substance plays a key role in the processes of life, because macroergic bonds between phosphate residues contain a huge amount of energy. Adenosine triphosphate performs many functions in the cell, and therefore it is important to maintain a constant concentration of the substance. Decay and synthesis proceed at a high speed, since the binding energy is constantly used in biochemical reactions. This is an indispensable substance of any cell in the body. That, perhaps, is all that can be said about the structure of ATP.