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. Nevertheless, they are destined to take second place after proteins, because the basis of life is just the polypetid molecule.
Nucleic acids are a different standard of living, much more complex and interesting due to the fact that each type of molecule does a job specific to it. This should be sorted out 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 may contain the hereditary information of some viruses. These are HIV and adenoviruses. There are also 2 special types of DNA: mitochondrial and plastid (located in chloroplasts).
RNA, on the other hand, has many more species, which is due to various functions of the nucleic acid. There is nuclear RNA that 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, what functions in the cell are performed by nucleic acids should be understood in more detail.
Double-stranded DNA molecule
This type of DNA is a perfect system for storing hereditary information. A 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 nitrogenous base, an orthophosphate residue, and a five-carbon deoxyribose monosaccharide. Depending on what type of nitrogenous base underlies a certain DNA monomer, it has its own name. Types of DNA Monomers:
- deoxyribose with the remainder of orthophosphate and adenyl nitrogenous base;
- thymidine nitrogenous base with deoxyribose and the remainder of orthophosphate;
- cytosine nitrogen base, desoxyribose and orthophosphate residue;
- orthophosphate with deoxyribose and guanine nitrogenous residue.
In the letter, to simplify the structure of DNA, the adenyl residue is indicated as “A”, guanine - “G”, thymidine - “T”, and cytosine - “C”. It is important that genetic information is transferred from a 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 thymidyl nitrogenous base, uracil is found in RNA.
DNA structure and function
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. The nucleotides of DNA are connected by covalent bonds. Then, according to the principle of complementarity, other nucleotides are attached to the nucleotides of a single-stranded molecule. If in a single-stranded molecule the beginning is represented by the nucleotide adenine, then in the second (complementary) chain, thymine will correspond to it. 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. Functions of double-stranded DNA:
- preservation of hereditary information received from the parent cell;
- gene expression;
- 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 are involved in gene expression. Nucleic acid itself is their storage location, and protein is the end result of reading information from a gene. The gene itself is a section of one complete DNA molecule packed into a chromosome, in which information on the structure of a particular protein is recorded by means of nucleotides. One gene encodes the amino acid sequence of only one protein. It is the protein that will realize the hereditary information.
Classification of RNA species
The functions of nucleic acids in a 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. Moreover, the following types of RNA exist:
- nuclear RNA of viruses and bacteria;
- matrix (informational) RNA;
- ribosomal RNA;
- matrix RNA plasmids (chloroplasts);
- ribosomal chloroplast RNA;
- mitochondrial ribosomal RNA;
- mitochondrial messenger RNA;
- transport RNA.
RNA Functions
This classification contains several types of RNA, which are divided according to 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. In this case, the amino acids are “brought” to the ribosomal RNA, “strung” on the messenger RNA, by means of transport ribonucleic acid. This is the synthesis of any organism that has ribosomes. The structure and functions of nucleic acids provide both the conservation of genetic material and the creation of protein synthesis processes.
Mitochondrial Nucleic Acids
If almost everything is known about what functions in a cell are nucleic acids located in the nucleus or cytoplasm, then there is little information about mitochondrial and plastid DNA. Specific ribosomal as well as messenger RNAs were found here. Nucleic acids of DNA and RNA are present even in the most autotrophic organisms.
Perhaps the nucleic acid entered the cell through 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 autophore bacterium got into 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, it is likely that the symbiont nuclear-free bacterium was driving the mutational processes in the nucleus of the host cell. This allowed the genes responsible for maintaining information about the structure of mitochondrial proteins to invade the nucleic acid of the host cell. However, so far there is not much information about what functions in a cell are performed by nucleic acids of mitochondrial origin.
It is likely that part of the proteins whose structure is not yet encoded by the nuclear DNA or host RNA is synthesized in mitochondria. It is also likely that the cell needs its own mechanism of protein synthesis only because many proteins synthesized in the cytoplasm cannot penetrate the double mitochondrial membrane. At the same time, these organelles generate energy, and therefore, if there is a channel or a specific carrier for the protein, it is 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 in the case of mitochondrial nucleic acids. It also has its own ribosomal, matrix, and transport RNA. Moreover, 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 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 its analogous chloroplastic system have. It is also not clear why cells need mitochondrial nucleic acids if the proteins (obviously, not all) are already encoded in nuclear DNA (or RNA, depending on the organism). Although some facts suggest that the protein synthesizing system of mitochondria and chloroplasts is responsible for the same functions as the DNA of the nucleus and RNA of the cytoplasm. They store hereditary information, reproduce it and transmit it to daughter cells.
Summary
It is important to understand what functions in a cell are performed by nucleic acids of nuclear, plastid and mitochondrial origin. This opens up many prospects for science, because the symbiont mechanism, according to which many autotrophic organisms appeared, can be reproduced today. This will allow you to get a new type of cell, perhaps even a human one. Although, it is too early to speak about the prospects for the introduction of multi-membrane plastid organelles into cells.
It is much more important to understand that in a cell nucleic acids are responsible for almost all processes. This is 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 ensures the further development of evolutionary processes.