Life – mysterious, complex, mysterious – is nothing more than a set of fairly large molecules and fairly simple chemical reactions. If you had to construct large molecules, you would have gone one of two ways. Or, as in the artisanal jewelry business, you began to build every molecule “from scratch”, doing a unique job each time. Either this way is used in modern building technologies – you would make a set of simple molecules from which you can collect a wide variety of larger molecules by combining modules in one way or another. It turns out that just such a modular structure has biological molecules. According to the theory of evolution, this should be the simplest way to large molecules, because, at the beginning of the evolutionary process, there was no need to design very complex molecules.
Vital activity requires energy. In particular, it is necessary that the energy produced in one place can be used in another. This function in the cell is carried out by an entire army of specialized molecules. Perhaps the most important of these is adenosine triphosphate (ATP) and adenosine diphosphate (ADP). Both molecules are arranged like this: a group of carbon, hydrogen and nitrogen atoms (called adenine) is attached to the ribose molecule (this is sugar), and all of this is attached to the tail of phosphates. From the names of molecules, it is clear that two phosphates are contained in the tail of ADP, and three in the tail of ATP. When a chemical process occurs in the cell, for example, photosynthesis, the energy that is generated goes to the addition of the third phosphate to the tail of ADP. The resulting ATP molecule is then transferred to other parts of the cell. There, the stored energy can be used in other chemical processes:
As we already mentioned, there are other molecules that carry energy in the cell. The set of such molecules is somewhat similar to the different options for paying bills. You can choose cash, bank transfer, credit card, etc. – depending on which method is more convenient for you. Similarly, the cell can use ATP (the equivalent of cash) or any other of a large set of more complex molecules to maintain its vital activity.
The main structural unit of proteins are molecules of amino acids. To understand what an amino acid is, imagine a set of atoms that have hydrogen on one side, oxygen and hydrogen connected to each other, and various other components in the middle. Just as beads are threaded onto a string, proteins are assembled from these amino acids-a hydrogen ion (H +) of one amino acid is combined with a hydroxyl ion (OH-) of another amino acid to form a water molecule. (Imagine how each time a two-amino acid molecule joins a drop of water between them.) Among proteins, the most important role is played by enzyme proteins (see Catalysts and enzymes) regulating chemical reactions in cells; but proteins are also important structural components of living organisms. For example,