What functions in the cell are the nucleic acids? Structure and functions of nucleic acids

Nucleic acids play an important role in the cell, ensuring its vital activity and reproduction. These properties make it possible to call them second important biomolecules after proteins. Many researchers even take DNA and RNA to the first place, implying their main importance in the development of life. Nevertheless, they are destined to take the second place after proteins, because the basis of life is just a polypeptide molecule.

Nucleic acids are another level of life, much more complex and interesting because each kind of molecule performs a specific job for it. This should be understood in more detail.

The concept of nucleic acids

All nucleic acids (DNA and RNA) are biological heterogeneous polymers that differ in the number of chains. DNA is a double-stranded polymer molecule that contains the genetic information of eukaryotic organisms. Ring DNA molecules can contain hereditary information of some viruses. These are HIV and adenoviruses. Also there are 2 special types of DNA: mitochondrial and plastid (found in chloroplasts).

RNA also has many more species, which is due to different functions of the nucleic acid. There is a nuclear RNA that contains hereditary information of bacteria and most viruses, matrix (or information RNA), ribosomal and transport. All of them participate either in the storage of hereditary information, or in the expression of genes. However, in what functions in the cell nucleic acids are performed, it is necessary to understand more in detail.

The double-stranded DNA molecule

This type of DNA is the perfect system for storing hereditary information. The double-stranded DNA molecule is a single molecule consisting of heterogeneous monomers. Their task is the formation of hydrogen bonds between the nucleotides of another chain. The DNA monomer itself consists of a nitrogen base, an orthophosphate residue and a five-carbon deoxyribose monosaccharide. Depending on which type of nitrogenous base lies at the base of a particular DNA monomer, it has its name. Types of DNA monomers:

• Deoxyribose with an orthophosphate residue and an adenylic nitrogen base;
• Thymidine nitrogen base with deoxyribose and orthophosphate residue;
• Cytosine nitrogen base, desoxyribose and orthophosphate residue;
• Orthophosphate with deoxyribose and guanine nitrogen residue.

In writing, to simplify the structure of DNA, the adenyl residue is designated as "A", guanine - "G", thymidine - "T", and cytosine - "C". It is important that genetic information is transferred from the double-stranded DNA molecule to the information RNA. There are few differences: here as a carbohydrate residue there is not a deoxyribose but a ribose, and instead of a thymidyl nitrogenous base in RNA, uracil is found.

Structure and function of DNA

DNA is built on the principle of a biological polymer, in which one chain is created in advance according to a given pattern, depending on the genetic information of the parent cell. Nucleotides of DNA are connected here by covalent bonds. Then, according to the principle of complementarity, other nucleotides are attached to the nucleotides of the single-stranded molecule. If in the single-stranded molecule the origin is represented by the nucleotide adenine, then in the second (complementary) chain it will correspond to thymine. Guanine is complementary to cytosine. Thus, a double-stranded DNA molecule is constructed. It is in the nucleus and stores hereditary information, which is encoded by codons - triplets of nucleotides. Functions of double-stranded DNA:

• Preservation of inherited information received from the parent cell;
• Gene expression;
• An obstacle to mutational changes.

The importance of proteins and nucleic acids

It is believed that the functions of proteins and nucleic acids are common, namely: they participate in the expression of genes. The nucleic acid itself is their storage place, and the protein is the end result of reading the information from the gene. The gene itself is the site of one complete DNA molecule, packed in a chromosome, in which information about the structure of a specific protein is recorded by nucleotides. One gene encodes the amino acid sequence of only one protein. It is the protein that will realize hereditary information.

Classification of RNA species

The functions of nucleic acids in the cell are very diverse. And they are most numerous in the case of RNA. However, this polyfunctionality is still relative, because one type of RNA is responsible for one of the functions. The following types of RNA exist:

• Nuclear RNA viruses and bacteria;
• Matrix (information) RNA;
• Ribosomal RNA;
• Matrix RNA of plasmids (chloroplasts);
• Ribosomal RNA of chloroplasts;
• Mitochondrial ribosomal RNA;
• Mitochondrial matrix RNA;
• Transport RNA.

RNA functions

This classification contains several types of RNA, which are separated depending on the location. However, in functional terms, they should be divided into 4 types: nuclear, information, ribosomal and transport. The function of ribosomal RNA is protein synthesis based on the nucleotide sequence of the information RNA. In this case, the amino acids are "brought" to the ribosomal RNA, "strung" on the information RNA, through transport ribonucleic acid. So the synthesis takes place in any organism that has ribosomes. The structure and functions of nucleic acids provide both the preservation of genetic material, and the creation of protein synthesis processes.

Mitochondrial nucleic acids

If the information about what functions in the cell is performed by nucleic acids located in the nucleus or the cytoplasm, practically everything is known, then the information about mitochondrial and plastid DNA is still not enough. Here, specific ribosomal as well as matrix RNAs were found. Nucleic acids DNA and RNA are present here even in the most autotrophic organisms.

Perhaps, the nucleic acid got into the cell by symbiogenesis. This path is considered by scientists as the most probable because of the lack of alternative explanations. The process is considered as follows: a symbiotic autorotrophic bacterium entered the cell within a certain period. As a result, this non-nuclear cell lives inside the cell and provides it with energy, but it gradually degrades.

At the initial stages of evolutionary development, it is likely that a symbiotic, non-nuclear bacterium has moved mutational processes in the nucleus of the host cell. This allowed the genes responsible for maintaining information about the structure of mitochondrial proteins to penetrate into the nucleic acid of the host cell. However, so far there is not much information about what functions in the cell are performed by nucleic acids of mitochondrial origin.

Probably, some proteins are synthesized in mitochondria, the structure of which is not yet encoded by nuclear DNA or host RNA. It is also likely that the protein synthesis mechanism is needed by the cell only because many proteins synthesized in the cytoplasm can not get through the double membrane of the mitochondria. At the same time, these organelles produce energy, and therefore, if there is a channel or a specific carrier for the protein, it is sufficient for the movement of the molecules and against the concentration gradient.

Plasmid DNA and RNA

Plastids (chloroplasts) also have their own DNA, which is probably responsible for the realization of similar functions, as in the case of mitochondrial nucleic acids. It also has its own ribosomal, matrix and transport RNA. And plastids, judging by the number of membranes, and not by the number of biochemical reactions, are more complicated. It happens that many plastids have 4 layers of membranes, which is explained by scientists in different ways.

One thing is clear: the functions of nucleic acids in the cell have not yet been fully studied. It is not known what importance the mitochondrial protein has to the synthesizing system and the chloroplastic analogous to it. It is also not entirely clear why cells need mitochondrial nucleic acids if proteins (obviously not all) are already encoded in nuclear DNA (or RNA, depending on the organism). Although some facts force us to agree that the protein synthesizing system of mitochondria and chloroplasts is responsible for the same functions as DNA of the nucleus and RNA of the cytoplasm. They preserve hereditary information, reproduce it and transmit it to the daughter cells.

Summary

It is important to understand what functions in the cell are performed by nucleic acids of nuclear, plastid and mitochondrial origin. This opens up a lot of prospects for science, because the symbiotic mechanism, according to which many autotrophic organisms have appeared, can be reproduced today. This will get a new type of cell, perhaps even human. Although it is too early to speak about the prospects for the introduction of many-membrane plastid organelles into cells.

It is much more important to understand that in the cell nucleic acids are responsible for virtually all processes. This is the biosynthesis of the protein, and the preservation of information about the structure of the cell. More importantly, nucleic acids serve as the transfer of hereditary material from the parent cells to the daughter cells. This guarantees the further development of evolutionary processes.