Plastic exchange is also called anabolism or assimilation and is the totality of all enzymatic biochemical reactions, as a result of which bioorganic compounds are synthesized.
Plastic metabolism includes the biosynthesis of proteins, lipids, carbohydrates, nucleic acids. Anabolism also undergoes the process of photosynthesis and chemosynthesis.
If we talk about plastic metabolism in the human body, then we must immediately say that all the nutrients that enter the body with food have a high molecular weight composition, and therefore can not be absorbed. In the process of digestion, these compounds decompose into individual monomers, which are already used for the synthesis of specific macromolecular substances inherent in the human body.
One of the most important classes of compounds are proteins. The protein nature of all the enzymes of the body, as well as some hormones. Proteins are hemoglobin (provides respiratory function), antibodies (provide the body's immune response), actin and myosin (determine muscle contraction), collagen and keratin (perform structural function in the body).
Given the important role of proteins for the functioning of the body, it is worth considering the process of their synthesis as an important part of plastic metabolism.
It must be said that all living organisms differ among themselves in the presence of specific proteins, which are composed of amino acids. It is the relative position of amino acids that determines the specific properties of protein compounds.
Proteins are synthesized in the cell cytoplasm on special organelles - ribosomes. These structures consist of large and small subunits. They take part in protein synthesis processes. An important role in the biosynthesis of proteins is played by nucleic acids, which include DNA and RNA. So, the structural units of DNA (genes) contain encoded information about the primary structure of proteins (a sequence of amino acids), and RNA is responsible for its reading and transport of amino acids to the place where protein synthesis takes place.
Protein synthesis occurs in two stages: transcription and translation. Transcription is based on the process of transferring protein structure information from DNA to RNA.
Translation is the direct synthesis of a polypeptide chain with the corresponding sequence of amino acids according to the genetic code with the participation of matrix (informational) RNA. The whole process of translation goes through three stages: initiation, elongation, termination. As a result of translation, a protein with a primary structure is formed.
It is worth remembering that plastic metabolism is not only the synthesis of proteins or other organic compounds, but also photosynthesis, which is a complex and multi-stage process, it takes place in 2 phases.
The light phase passes in chloroplasts (on thylakoids), in this case ATP is formed and molecular oxygen is released, and the dark phase passes in the main substance of chloroplasts and determines the absorption of carbon dioxide and the formation of carbohydrates.
I think we should not dwell on the role of photosynthesis, suffice it to say that thanks to this process, about 150 billion tons of organic substances, as well as about 200 billion tons of oxygen, are formed annually.
It must be said that plastic metabolism is closely related to the energy processes that occur in the body. Thus, energy metabolism (catabolism) is the opposite process of anabolism and includes all the splitting reactions when complex compounds decompose into simple ones, and high-molecular substances turn into a number of low-molecular ones. This releases energy that is used in plastic exchange processes.
So, plastic and energy metabolism in the cell form the basis of general metabolism - metabolism, which includes all the processes of synthesis and decomposition of substances.