It is well known that all forms of living matter, from viruses to highly organized animals (including humans), have a unique hereditary apparatus. It is represented by molecules of two types of nucleic acids: deoxyribonucleic and ribonucleic. In these organic substances, information is encoded that is transmitted from parent individuals to offspring during reproduction. In this work, we will study both the structure and functions of DNA and RNA in the cell, and also consider the mechanisms underlying the processes of transferring the hereditary properties of living matter.
As it turned out, the properties of nucleic acids, although they have some common features, nevertheless differ in many ways. Therefore, we will compare the functions of DNA and RNA carried out by these biopolymers in cells of various groups of organisms. The table presented in the work will help to understand what is their fundamental difference.
Nucleic acids –complex biopolymers
Discoveries in the field of molecular biology that occurred at the beginning of the 20th century, in particular, the deciphering of the structure of deoxyribonucleic acid, served as an impetus for the development of modern cytology, genetics, biotechnology and genetic engineering. From the point of view of organic chemistry, DNA and RNA are macromolecular substances consisting of repeatedly repeating units - monomers, also called nucleotides. It is known that they are interconnected, forming chains capable of spatial self-organization.
Such DNA macromolecules often bind to special proteins with special properties called histones. Nucleoprotein complexes form special structures - nucleosomes, which, in turn, are part of chromosomes. Nucleic acids can be found both in the nucleus and in the cytoplasm of the cell, present in some of its organelles, such as mitochondria or chloroplasts.
Spatial structure of the substance of heredity
To understand the functions of DNA and RNA, you need to understand in detail the features of their structure. Like proteins, nucleic acids have several levels of organization of macromolecules. The primary structure is represented by polynucleotide chains, the secondary and tertiary configurations are self-complicated due to the emerging covalent type of bond. A special role in maintaining the spatial shape of molecules belongs to hydrogen bonds, as well as van der Waals forces of interaction. The result is a compactthe structure of DNA, called the supercoil.
Nucleic acid monomers
The structure and functions of DNA, RNA, proteins and other organic polymers depend on both the qualitative and quantitative composition of their macromolecules. Both types of nucleic acids are made up of building blocks called nucleotides. As is known from the course of chemistry, the structure of a substance necessarily affects its functions. DNA and RNA are no exception. It turns out that the type of acid itself and its role in the cell depend on the nucleotide composition. Each monomer contains three parts: a nitrogenous base, a carbohydrate, and a phosphoric acid residue. There are four types of nitrogenous bases for DNA: adenine, guanine, thymine and cytosine. In RNA molecules, they will be, respectively, adenine, guanine, cytosine and uracil. Carbohydrate is represented by various types of pentose. Ribonucleic acid contains ribose, while DNA contains its deoxygenated form, called deoxyribose.
Features of deoxyribonucleic acid
First, we will look at the structure and functions of DNA. RNA, which has a simpler spatial configuration, will be studied by us in the next section. So, two polynucleotide strands are held together by repeatedly repeating hydrogen bonds formed between nitrogenous bases. In the pair "adenine - thymine" there are two, and in the pair "guanine - cytosine" there are three hydrogen bonds.
The conservative correspondence of purine and pyrimidine bases wasdiscovered by E. Chargaff and was called the principle of complementarity. In a single chain, the nucleotides are linked together by phosphodiester bonds formed between the pentose and the orthophosphoric acid residue of adjacent nucleotides. The helical form of both chains is supported by hydrogen bonds that occur between the hydrogen and oxygen atoms that are part of the nucleotides. The higher - tertiary structure (supercoil) - is characteristic of the nuclear DNA of eukaryotic cells. In this form, it is present in chromatin. However, bacteria and DNA-containing viruses have deoxyribonucleic acid that is not associated with proteins. It is represented by a ring-shaped form and is called a plasmid.
The DNA of mitochondria and chloroplasts, organelles of plant and animal cells, has the same look. Next, we will find out how the functions of DNA and RNA differ from each other. The table below will show us these differences in the structure and properties of nucleic acids.
Ribonucleic acid
The RNA molecule consists of one polynucleotide strand (the exception is the double-stranded structures of some viruses), which can be located both in the nucleus and in the cell cytoplasm. There are several types of ribonucleic acids, which differ in structure and properties. Thus, messenger RNA has the highest molecular weight. It is synthesized in the cell nucleus on one of the genes. The task of mRNA is to transfer information about the composition of the protein from the nucleus to the cytoplasm. Transport form of nucleic acid attaches protein monomers– amino acids - and delivers them to the place of biosynthesis.
Finally, ribosomal RNA is formed in the nucleolus and is involved in protein synthesis. As you can see, the functions of DNA and RNA in cellular metabolism are diverse and very important. They will depend, first of all, on the cells of which organisms contain the molecules of the substance of heredity. So, in viruses, ribonucleic acid can act as a carrier of hereditary information, while in the cells of eukaryotic organisms, only deoxyribonucleic acid has this ability.
Functions of DNA and RNA in the body
According to their importance, nucleic acids, along with proteins, are the most important organic compounds. They preserve and transmit hereditary properties and traits from parent to offspring. Let's define the difference between the functions of DNA and RNA. The table below will show these differences in more detail.
| View | Place in a cage | Configuration | Function |
| DNA | core | superspiral | preservation and transmission of hereditary information |
| DNA |
mitochondria chloroplasts |
circular (plasmid) | local transmission of hereditary information |
| iRNA | cytoplasm | linear | removal of information from the gene |
| tRNA | cytoplasm | secondary | transport of amino acids |
| rRNA | core andcytoplasm | linear | formation of ribosomes |
What are the characteristics of the substance of the heredity of viruses?
Nucleic acids of viruses can be in the form of both single-stranded and double-stranded helices or rings. According to D. B altimore's classification, these objects of the microcosm contain DNA molecules consisting of one or two chains. The first group includes herpes pathogens and adenoviruses, and the second includes, for example, parvoviruses.
The functions of DNA and RNA viruses are to penetrate their own hereditary information into the cell, carry out replication reactions of viral nucleic acid molecules and assemble protein particles in the ribosomes of the host cell. As a result, the entire cellular metabolism is completely subordinated to parasites, which, rapidly multiplying, lead the cell to death.
RNA viruses
In virology, it is customary to divide these organisms into several groups. So, the first includes species that are called single-stranded (+) RNA. Their nucleic acid performs the same functions as the messenger RNA of eukaryotic cells. Another group includes single-stranded (-) RNAs. First, transcription occurs with their molecules, leading to the appearance of (+) RNA molecules, and those, in turn, serve as a template for assembling viral proteins.
Based on the foregoing, for all organisms, including viruses, the functions of DNA and RNA are briefly characterized as follows: storage of hereditary characteristics and properties of the organism and their further transmission to offspring.
