Structure and function of DNA and RNA (Table)
It is well known that all forms of living matter,ranging from viruses to highly organized animals (including humans), have a unique hereditary apparatus. It is represented by molecules of two kinds of nucleic acids: deoxyribonucleic and ribonucleic. In these organic substances, information that is transmitted from the parent to the offspring during reproduction is encoded. In this paper we will study both the structure and functions of DNA and RNA in a cell, and also consider the mechanisms underlying the processes of transferring hereditary properties of living matter.
As it turned out, the properties of nucleic acids, althoughand have some common features, nevertheless, in many respects differ among themselves. Therefore, we compare the functions of DNA and RNA, carried out by these biopolymers in the cells of different groups of organisms. The table presented in the paper will help to understand what is their fundamental difference.
Nucleic acids - complex biopolymers
Discoveries in the field of molecular biology,which occurred in the early twentieth century, in particular, the decoding 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 high molecular substances consisting of repeatedly repeating units - monomers, also called nucleotides. It is known that they are connected to each other, forming chains capable of spatial self-organization.
Such macromolecules of DNA often bind tospecial proteins, which have special properties and are called histones. Nucleoprotein complexes form special structures - nucleosomes, which, in turn, are part of the chromosomes. Nucleic acids can be found both in the nucleus and in the cytoplasm of the cell, being present in some of its organelles, for example, mitochondria or chloroplasts.
Spatial structure of the substance of heredity
To understand the functions of DNA and RNA, you need to detailto understand the peculiarities of their structure. Like proteins, nucleic acids, several levels of organization of macromolecules are inherent. The primary structure is represented by polynucleotide chains, the secondary and tertiary configurations self-contract due to the emerging covalent bond type. A special role in maintaining the spatial shape of the molecules belongs to hydrogen bonds, as well as van der Waals forces of interaction. As a result, a compact DNA structure is formed, called super-helix.
Monomers of nucleic acids
The structure and function of DNA, RNA, proteins and otherorganic polymers depend both on the qualitative and quantitative composition of their macromolecules. Both kinds of nucleic acids consist of structural elements called nucleotides. As is known from the chemistry course, the structure of a substance necessarily affects its function. DNA and RNA are no exception. It turns out that the kind 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 an orthophosphoric 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 kinds of pentose. In ribonucleic acid is ribose, and in DNA - its deoxygenated form, called deoxyribose.
Features of deoxyribonucleic acid
First, we'll look at the structure and functions of DNA. RNA, which has a simpler spatial configuration, will be studied by us in the next section. Thus, two polynucleotide strands are held together by repeatedly repeating hydrogen bonds formed between the nitrogenous bases. In the pair "adenine - thymine" there are two, and in the pair "guanine - cytosine" - three hydrogen bonds.
Conservative compliance of purine andpyrimidine bases was discovered 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 a series of located nucleotides. The spiral form of both chains is maintained by hydrogen bonds arising between the hydrogen and oxygen atoms in the nucleotide. Higher - tertiary structure (supercoiled) - is characteristic for nuclear DNA of eukaryotic cells. In this form, it is present in the chromatin. However, bacteria and DNA-containing viruses have deoxyribonucleic acid, not associated with proteins. It is represented by an annular shape and is called a plasmid.
The same kind of DNA has mitochondria and chloroplasts- organelles of plant and animal cells. Next, we will find out what is the difference between the functions of DNA and RNA. The table below will show us these differences in the structure and properties of nucleic acids.
The RNA molecule consists of one polynucleotideThreads (the double-strand structures of some viruses are an exception), which can be found both in the nucleus and in the cell cytoplasm. There are several types of ribonucleic acids, which differ in structure and properties. Thus, the information RNA has the largest molecular weight. It is synthesized in the nucleus of a cell on one of the genes. The task of mRNA is to transfer information about the protein composition from the nucleus to the cytoplasm. The transport form of the nucleic acid attaches monomers of proteins - amino acids - and delivers them to the site of biosynthesis.
Finally, ribosomal RNA is formed in the nucleolus andparticipates 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 are the molecules of the substance of heredity. Thus, in viruses, ribonucleic acid can act as a carrier of hereditary information, whereas in cells of eukaryotic organisms this ability has only deoxyribonucleic acid.
Functions of DNA and RNA in the body
By its value, nucleic acids, along withproteins, are the most important organic compounds. They preserve and transmit hereditary properties and attributes from the parent to the offspring. Let's determine 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||supercoiling||preservation and transfer of hereditary information|
|annular (plasmid)||local transfer of hereditary information|
|mRNA||cytoplasm||linear||removal of information from the gene|
|tRNA||cytoplasm||secondary||amino acid transport|
|rRNA||nucleus and cytoplasm||linear||ribosome formation|
What are the characteristics of the substance of heredity of viruses?
Nucleic acids of viruses can be of the formsingle- and double-stranded spirals or rings. According to D. Baltimore's classification, these objects of the microworld contain DNA molecules consisting of one or two chains. The first group includes herpes pathogens and adenoviruses, and the second group includes, for example, parvoviruses.
The functions of DNA and RNA viruses arepenetration of own hereditary information into the cell, carrying out replication reactions of viral nucleic acid molecules and assembling protein particles in the ribosomes of the host cell. As a result, the entire cellular metabolism is completely subordinate to the parasites, which, rapidly multiplying, lead the cell to death.
In virology, the division of these organismson several groups. Thus, the first includes species called single-stranded (+) RNA. They nucleic acid performs the same functions as the information RNA of eukaryotic cells. The other group includes single-stranded (-) RNA. First, with their molecules, transcription occurs, leading to the appearance of molecules (+) RNA, and they, in turn, serve as a matrix for the assembly of viral proteins.
Based on the above, for allorganisms, including viruses, the functions of DNA and RNA are briefly characterized as follows: storage of hereditary traits and properties of the organism and further transfer to their offspring.