Millions of biochemical reactions take place in every cell of our body. They are catalyzed by a variety of enzymes, which often require energy. Where does the cell take it? This question can be answered if we consider the structure of the molecule ATP – one of the main sources of energy.
ATP – a universal source of energy
ATP stands for adenosine triphosphate, or adenosine triphosphoric acid. 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 take place only with the participation of substance molecules, especially with regard to plastic metabolism. However, ATP is rarely directly involved in the reaction: for the course of any process, energy is needed, which is contained precisely in the chemical bonds of adenosine triphosphate.
The structure of the substance molecules is such that the resulting bonds between phosphate groups carry a huge amount of energy. Therefore, such connections are also called macroergic, or macroenergy (macro = many, large number). The term macroergic connections were first introduced by the scientist F. Lipman, and he suggested using the значок symbol to denote them.
It is very important for the cell to maintain a constant level of adenosine triphosphate. This is especially characteristic of muscle cells and nerve fibers, because they are the most volatile and in order to perform their functions require 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 pentose group. This means that the composition of ribose contains 5 carbon atoms, which are enclosed in a cycle. Ribose binds to the adenine β-N-glycosidic bond on the 1st carbon atom. Also to the pentose are attached residues of phosphoric acid on the 5th carbon atom.
Adenine is a nitrogen base. Depending on which nitrogenous base joins the ribose, GTP (guanosine triphosphate), TTF (timidine triphosphate), CTP (cytidriphosphate) and UTP (uridine triphosphate) are also isolated. All these substances are similar in structure to adenosine triphosphate and perform approximately the same functions, but they are found in the cell much less frequently.
Phosphoric acid residues. A maximum of three phosphoric acid residues may join ribose. If there are two or only one, then the substance is called ADP (diphosphate) or AMP (monophosphate), respectively. It is between the phosphorus residues that the macroenergy bonds are made, after breaking which from 40 to 60 kJ of energy is released. If two bonds are broken, 80 are allocated, less often – 120 kJ of energy. When the bond between the ribose and the phosphorus residue is broken, only 13.8 kJ is released, so there are only two high energy bonds in the triphosphate molecule (P ̴ P ̴ P) and one in the ADP molecule (P ̴ P).
Here are the features of the structure of ATP. Due to the fact that between the residues of phosphoric acid a macroenergy bond is formed, 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, GTP, TTF, CTP and UTP are suppliers of nitrogenous bases. This property is used in the processes of DNA replication and transcription.
ATP is also required 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 the channel can function. The same applies to the proton and calcium channels.
ATP is a precursor of the cAMP secondary messenger (cyclic adenosine monophosphate) – cAMP not only transmits the signal received by cell membrane receptors, but is also an allosteric effector. Allosteric effectors are substances that speed up 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, in such processes an ATP antagonist is ADP: if triphosphate accelerates the reaction, the diphosphate inhibits, and vice versa. These are the functions and structure of ATP.
How is ATP formed in the cell?
The functions and structure of ATP are such that substance molecules are quickly used and destroyed. Therefore, the synthesis of triphosphate is an important process of formation of energy in the cell.
There are three most important ways to synthesize adenosine triphosphate:
1. Substrate phosphorylation.
2. Oxidative phosphorylation.
Substrate phosphorylation is based on multiple reactions occurring in the cytoplasm of the cell. These reactions are called glycolysis – the anaerobic stage of aerobic respiration. As a result of 1 cycle of glycolysis, two molecules of pyruvic acid are synthesized from 1 molecule of glucose, which are further used for energy, and two ATP are also synthesized.
Oxidative phosphorylation. Cell breathing
Oxidative phosphorylation is the formation of adenosine triphosphate by transferring electrons through the electron transport chain of a membrane. As a result of this transfer, a proton gradient is formed on one side of the membrane and the molecules are built using the protein integral set of ATP synthase. The process takes place on the mitochondrial membrane.
The sequence of glycolysis and oxidative phosphorylation in mitochondria is a common process called respiration. After a full cycle of 1 molecule of glucose in the cell 36 ATP molecules are formed.
The process of photophosphorylation is the same oxidative phosphorylation with only one difference: photophosphorylation reactions take place in the chloroplasts of the cell under the action of light. ATP is formed during the light stage of photosynthesis – the main process of obtaining energy from green plants, algae and some bacteria.
In the process of photosynthesis, electrons pass through the same electron transport chain, as a result of which a proton gradient is formed. The concentration of protons on one side of the membrane is the 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% adenosine triphosphate from the total mass. However, the highest 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 molecule of adenosine triphosphate is updated 2000-3000 times per day.
– In total, the human body synthesizes 40 kg of adenosine triphosphate per day, and at every instant of time ATP is 250 g.
The structure of ATP and the biological role of its molecules are closely related. The substance plays a key role in the processes of vital activity, because in energy-rich bonds between phosphate residues contains 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 with great speed, since the energy of bonds is constantly used in biochemical reactions. It is an indispensable substance of any cell in the body. Here, perhaps, is all that can be said about the structure of ATP.