Nucleic acids play an important role in the cell, ensuring its vital activity and reproduction. These properties make it possible to call them the second most important biological molecules after proteins. Many researchers even put DNA and RNA in the first place, implying their main importance in the development of life. However, they are destined to take second place after proteins, because the basis of life is precisely the polypeptide molecule.
Nucleic acids are a different level of life, much more complex and interesting due to the fact that each kind of molecule does a specific job for it. This should be looked into 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 containsgenetic information of eukaryotic organisms. Circular DNA molecules may contain the hereditary information of some viruses. These are HIV and adenoviruses. There are also 2 special types of DNA: mitochondrial and plastid (found in chloroplasts).
RNA, on the other hand, has many more types, due to the different functions of the nucleic acid. There is nuclear RNA, which contains the hereditary information of bacteria and most viruses, matrix (or messenger RNA), ribosomal and transport. All of them are involved either in the storage of hereditary information or in gene expression. However, it is necessary to understand in more detail what functions nucleic acids perform in the cell.
Double stranded DNA molecule
This type of DNA is a perfect storage system for hereditary information. A double-stranded DNA molecule is a single molecule composed of heterogeneous monomers. Their task is to form hydrogen bonds between nucleotides of another chain. The DNA monomer itself consists of a nitrogenous base, an orthophosphate residue, and a five-carbon monosaccharide deoxyribose. Depending on what type of nitrogenous base underlies a particular DNA monomer, it has its own name. Types of DNA monomers:
- deoxyribose with an orthophosphate residue and an adenyl nitrogenous base;
- thymidine nitrogenous base with deoxyribose and an orthophosphate residue;
- cytosine nitrogen base, deoxyribose and orthophosphate residue;
- orthophosphate with deoxyribose and guanine nitrogenous residue.
In writing, to simplify the DNA structure scheme, the adenyl residue is designated as "A", the guanine residue is designated as "G", the thymidine residue is "T", and the cytosine residue is "C". It is important that genetic information is transferred from the double-stranded DNA molecule to messenger RNA. It has few differences: here, as a carbohydrate residue, there is not deoxyribose, but ribose, and instead of the thymidyl nitrogenous base, uracil occurs in RNA.
Structure and functions of DNA
DNA is built on the principle of a biological polymer, in which one chain is created in advance according to a given template, depending on the genetic information of the parent cell. DNA nucleotides 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 a single-stranded molecule the beginning 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 built. It is located in the nucleus and stores hereditary information, which is encoded by codons - triplets of nucleotides. Double-stranded DNA functions:
- preservation of hereditary information received from the parent cell;
- gene expression;
- prevention of mutational changes.
The importance of proteins and nucleic acids
It is believed that the functions of proteins and nucleic acids are common, namely:they are involved in gene expression. The nucleic acid itself is their place of storage, and the protein is the end result of reading information from the gene. The gene itself is a section of one integral DNA molecule, packed into a chromosome, in which information about the structure of a certain protein is recorded by means of nucleotides. One gene codes for the amino acid sequence of only one protein. It is the protein that will implement the hereditary information.
Classification of RNA types
The functions of nucleic acids in the cell are very diverse. And they are most numerous in the case of RNA. However, this multifunctionality is still relative, because one type of RNA is responsible for one of the functions. In this case, there are the following types of RNA:
- nuclear RNA of viruses and bacteria;
- matrix (information) RNA;
- ribosomal RNA;
- messenger RNA plasmid (chloroplast);
- Chloroplast ribosomal RNA;
- mitochondrial ribosomal RNA;
- mitochondrial messenger RNA;
- transfer RNA.
RNA Functions
This classification contains several types of RNA, which are divided depending on the location. However, in functional terms, they should be divided into only 4 types: nuclear, informational, ribosomal and transport. The function of ribosomal RNA is protein synthesis based on the nucleotide sequence of messenger RNA. Whereinamino acids are "brought" to the ribosomal RNA, "strung" on the messenger RNA, by means of a transport ribonucleic acid. This is how synthesis proceeds 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 almost everything is known about the functions in the cell performed by nucleic acids located in the nucleus or cytoplasm, then there is still little information about mitochondrial and plastid DNA. Specific ribosomal and messenger RNAs have also been found here. Nucleic acids DNA and RNA are present here even in the most autotrophic organisms.
Perhaps the nucleic acid entered the cell by symbiogenesis. This path is considered by scientists as the most likely due to the lack of alternative explanations. The process is considered as follows: a symbiotic autotrophic bacterium got inside the cell at a certain period. As a result, this nuclear-free cell lives inside the cell and provides it with energy, but gradually degrades.
At the initial stages of evolutionary development, probably, a symbiotic non-nuclear bacterium moved mutation processes in the nucleus of the host cell. This allowed the genes responsible for storing information about the structure of mitochondrial proteins to be introduced into the nucleic acid of the host cell. However, for now, what functions in the cell are performed by nucleic acids of mitochondrial origin,not much information.
Probably, some proteins are synthesized in the mitochondria, the structure of which is not yet encoded by the host's nuclear DNA or RNA. It is also likely that the cell needs its own mechanism of protein synthesis only because many proteins synthesized in the cytoplasm cannot 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 will be enough for the movement of molecules and against the concentration gradient.
Plasmid DNA and RNA
Plastids (chloroplasts) also have their own DNA, which is probably responsible for the implementation of similar functions, as is the case with mitochondrial nucleic acids. It also has its own ribosomal, messenger and transfer RNA. Moreover, plastids, judging by the number of membranes, and not by the number of biochemical reactions, are more complex. It happens that many plastids have 4 layers of membranes, which is explained by scientists in different ways.
One thing is obvious: the functions of nucleic acids in the cell have not yet been fully studied. It is not known what significance the mitochondrial protein-synthesizing system and the analogous chloroplastic system have. 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 asand DNA of the nucleus and RNA of the cytoplasm. They store hereditary information, reproduce it and pass it on to daughter cells.
CV
It is important to understand what functions in the cell perform nucleic acids of nuclear, plastid and mitochondrial origin. This opens up many prospects for science, because the symbiotic mechanism, according to which many autotrophic organisms appeared, can be reproduced today. This will make it possible to obtain a new type of cell, perhaps even a human one. Although it is too early to talk about the prospects for the introduction of multi-membrane plastid organelles into cells.
It is much more important to understand that nucleic acids are responsible for almost all processes in a cell. This is both protein biosynthesis and the preservation of information about the structure of the cell. Moreover, it is much more important that nucleic acids perform the function of transferring hereditary material from parent cells to daughter cells. This guarantees the further development of evolutionary processes.
