The times we live in are marked by amazing changes, huge progress, where people get answers to more and more questions. Life is rapidly moving forward, and what until recently seemed impossible is beginning to come true. It is quite possible that what today seems to be a plot from the science fiction genre will soon also acquire the features of reality.
One of the most important discoveries in the second half of the twentieth century was the nucleic acids RNA and DNA, thanks to which man came closer to unraveling the mysteries of nature.
Nucleic acids
Nucleic acids are organic compounds with macromolecular properties. They are composed of hydrogen, carbon, nitrogen and phosphorus.
They were discovered in 1869 by F. Miescher, who examined pus. However, at that time his discovery was not given much importance. Only later, when these acids were found in all animal and plant cells, did the understanding of their enormous role come.
There are two types of nucleic acids: RNA and DNA (ribonucleic and deoxyribonucleicacids). This article is about ribonucleic acid, but for a general understanding, let's also consider what DNA is.
What is deoxyribonucleic acid?
DNA is a nucleic acid consisting of two strands that are connected according to the law of complementarity by hydrogen bonds of nitrogenous bases. Long chains are twisted into a spiral, one turn contains almost ten nucleotides. The diameter of the double helix is two millimeters, the distance between nucleotides is about half a nanometer. The length of one molecule sometimes reaches several centimeters. The length of the DNA of the nucleus of a human cell is almost two meters.
The structure of DNA contains all genetic information. DNA has replication, which means the process during which two absolutely identical daughter molecules are formed from one molecule.
As already noted, the chain is made up of nucleotides, which in turn consist of nitrogenous bases (adenine, guanine, thymine and cytosine) and a phosphorus acid residue. All nucleotides differ in nitrogenous bases. Hydrogen bonding does not occur between all bases; adenine, for example, can only combine with thymine or guanine. Thus, there are as many adenyl nucleotides in the body as thymidyl nucleotides, and the number of guanyl nucleotides is equal to cytidyl nucleotides (Chargaff's rule). It turns out that the sequence of one chain predetermines the sequence of another, and the chains seem to mirror each other. Such a pattern, where the nucleotides of two chains are arranged in an orderly manner, and are also connected selectively, is calledthe principle of complementarity. In addition to hydrogen compounds, the double helix also interacts hydrophobically.
Two chains are in opposite directions, that is, they are located in opposite directions. Therefore, opposite the three'-end of one is the five'-end of the other chain.
Outwardly, the DNA molecule resembles a spiral staircase, the railing of which is a sugar-phosphate backbone, and the steps are complementary nitrogen bases.
What is ribonucleic acid?
RNA is a nucleic acid with monomers called ribonucleotides.
In chemical properties, it is very similar to DNA, since both are polymers of nucleotides, which are a phosphorylated N-glycoside, which is built on a pentose (five-carbon sugar) residue, with a phosphate group on the fifth carbon atom and a nitrogen base at the first carbon atom.
It is a single polynucleotide chain (except for viruses), which is much shorter than that of DNA.
One RNA monomer is the residues of the following substances:
- nitrogen bases;
- five-carbon monosaccharide;
- phosphorus acids.
RNAs have pyrimidine (uracil and cytosine) and purine (adenine, guanine) bases. Ribose is the monosaccharide of the RNA nucleotide.
Differences between RNA and DNA
Nucleic acids differ from each other in the following ways:
- its quantity in a cell depends on the physiological state, age and organ affiliation;
- DNA contains carbohydratedeoxyribose, and RNA - ribose;
- The nitrogenous base in DNA is thymine, and in RNA it is uracil;
- classes perform different functions, but are synthesized on the DNA matrix;
- DNA is double helix, RNA is single strand;
- not typical for her DNA Chargaff rules;
- RNA has more minor bases;
- chains vary significantly in length.
Study history
The RNA cell was first discovered by German biochemist R. Altman while studying yeast cells. In the middle of the twentieth century, the role of DNA in genetics was proven. Only then were RNA types, functions, and so on described. Up to 80-90% of the mass in the cell falls on rRNA, which together with proteins form the ribosome and participate in protein biosynthesis.
In the sixties of the last century, it was first suggested that there must be a certain species that carries the genetic information for protein synthesis. After that, it was scientifically established that there are such informational ribonucleic acids representing complementary copies of genes. They are also called messenger RNAs.
The so-called transport acids are involved in decoding the information recorded in them.
Later, methods began to be developed to identify the sequence of nucleotides and establish the structure of RNA in the acid space. So it was found that some of them, which were called ribozymes, can cleave polyribonucleotide chains. As a result, it began to be assumed that at the time when life was emerging on the planet,RNA worked without DNA and proteins. Moreover, all the transformations were made with her participation.
The structure of the ribonucleic acid molecule
Almost all RNAs are single chains of polynucleotides, which, in turn, consist of monoribonucleotides - purine and pyrimidine bases.
Nucleotides are denoted by the initial letters of the bases:
- adenine (A), A;
- guanine (G), G;
- cytosine (C), C;
- uracil (U), U.
They are linked by three- and five-phosphodiester bonds.
The most varied number of nucleotides (from several tens to tens of thousands) is included in the structure of RNA. They can form a secondary structure consisting mainly of short double-stranded strands that are formed by complementary bases.
Structure of a ribnucleic acid molecule
As already mentioned, the molecule has a single-stranded structure. RNA receives its secondary structure and shape as a result of the interaction of nucleotides with each other. It is a polymer whose monomer is a nucleotide consisting of a sugar, a phosphorus acid residue and a nitrogen base. Outwardly, the molecule is similar to one of the DNA chains. Nucleotides adenine and guanine, which are part of RNA, are purine. Cytosine and uracil are pyrimidine bases.
Synthesis process
For an RNA molecule to be synthesized, the template is a DNA molecule. True, the reverse process also happens, when new molecules of deoxyribonucleic acid are formed on the ribonucleic acid matrix. Suchoccurs during the replication of certain types of viruses.
The basis for biosynthesis can also serve as other molecules of ribonucleic acid. Its transcription, which occurs in the cell nucleus, involves many enzymes, but the most significant of them is RNA polymerase.
Views
Depending on the type of RNA, its functions also differ. There are several types:
- informational i-RNA;
- ribosomal rRNA;
- transport t-RNA;
- minor;
- ribozymes;
- viral.
Informational Ribonucleic Acid
Such molecules are also called matrix. They make up about two percent of the total in the cell. In eukaryotic cells, they are synthesized in the nuclei on DNA templates, then passing into the cytoplasm and binding to ribosomes. Further, they become templates for protein synthesis: they are joined by transfer RNAs that carry amino acids. This is how the process of information transformation takes place, which is realized in the unique structure of the protein. In some viral RNAs, it is also a chromosome.
Jacob and Mano are the discoverers of this species. Not having a rigid structure, its chain forms curved loops. Not working, i-RNA gathers into folds and folds into a ball, and unfolds in working condition.
i-RNA carries information about the sequence of amino acids in the protein that is being synthesized. Each amino acid is encoded in a specific location using genetic codes that are:
- tripletity - from four mononucleotides it is possible to build sixty-four codons (genetic code);
- non-crossing - information moves in one direction;
- continuity - the principle of operation is that one mRNA is one protein;
- universality - one or another type of amino acid is encoded in all living organisms in the same way;
- degeneracy - twenty amino acids are known, and sixty-one codons, that is, they are encoded by several genetic codes.
Ribosomal ribonucleic acid
Such molecules make up the vast majority of cellular RNA, namely eighty to ninety percent of the total. They combine with proteins and form ribosomes - these are organelles that perform protein synthesis.
Ribosome is 65% rRNA and 35% protein. This polynucleotide chain easily folds along with the protein.
The ribosome consists of amino acid and peptide regions. They are located on the contact surfaces.
Ribosomes move freely in the cell, synthesizing proteins in the right places. They are not very specific and can not only read information from mRNA, but also form a matrix with them.
Transport ribonucleic acid
t-RNA is the most studied. They make up ten percent of cellular ribonucleic acid. These types of RNA bind to amino acids thanks to a special enzyme and are delivered to ribosomes. At the same time, amino acids are transported by transportmolecules. However, it happens that different codons code for an amino acid. Then several transport RNAs will carry them.
It curls up into a ball when inactive, but functions like a cloverleaf.
The following sections are distinguished in it:
- acceptor stem having the nucleotide sequence of ACC;
- site for attaching to the ribosome;
- an anticodon encoding the amino acid attached to this tRNA.
Minor species of ribonucleic acid
Recently, RNA species have been replenished with a new class, the so-called small RNA. They are most likely universal regulators that turn genes on or off in embryonic development, as well as control processes within cells.
Ribozymes are also recently identified, they are actively involved when RNA acid is fermented, acting as a catalyst.
Viral types of acids
The virus can contain either ribonucleic acid or deoxyribonucleic acid. Therefore, with the corresponding molecules, they are called RNA-containing. When such a virus enters a cell, reverse transcription occurs - new DNA appears on the basis of ribonucleic acid, which are integrated into cells, ensuring the existence and reproduction of the virus. In another case, the formation of complementary RNA occurs on the incoming RNA. Viruses are proteins, life and reproduction goes on without DNA, but only on the basis of the information contained in the RNA of the virus.
Replication
In order to improve common understanding, it is necessaryConsider the process of replication that produces two identical nucleic acid molecules. This is how cell division begins.
It involves DNA polymerases, DNA-dependent, RNA polymerases and DNA ligases.
The replication process consists of the following steps:
- despiralization - there is a sequential unwinding of the maternal DNA, capturing the entire molecule;
- breaking of hydrogen bonds, in which the chains diverge, and a replication fork appears;
- adjustment of dNTPs to the released bases of the parent chains;
- cleavage of pyrophosphates from dNTP molecules and formation of phosphorodiester bonds due to released energy;
- respiralization.
After the formation of the daughter molecule, the nucleus, cytoplasm and the rest are divided. Thus, two daughter cells are formed that have completely received all the genetic information.
In addition, the primary structure of proteins that are synthesized in the cell is encoded. DNA takes an indirect part in this process, and not direct, which consists in the fact that it is on DNA that the synthesis of proteins, RNA involved in the formation, takes place. This process is called transcription.
Transcription
The synthesis of all molecules occurs during transcription, that is, the rewriting of genetic information from a specific DNA operon. The process is similar to replication in some ways, and very different in others.
The similarities are the following parts:
- starts with DNA despiralization;
- hydrogen rupture occursconnections between the bases of the chains;
- NTFs complementary to them;
- hydrogen bonds are formed.
Differences from replication:
- during transcription, only the portion of DNA corresponding to the transcripton is untwisted, while during replication, the entire molecule is untwisted;
- when transcribed, tunable NTFs contain ribose, and uracil instead of thymine;
- information is written off only from a certain area;
- after the formation of the molecule, the hydrogen bonds and the synthesized chain are broken, and the chain slips off the DNA.
For normal functioning, the primary structure of RNA should consist only of DNA sections copied from exons.
The maturation process begins in the newly formed RNA. Silent regions are excised, and informative regions are fused to form a polynucleotide chain. Further, each species has its own transformations.
In i-RNA, attachment to the initial end occurs. Polyadenylate is attached to the final site.
TRNA bases are modified to form minor species.
In rRNA, individual bases are also methylated.
Protect proteins from destruction and improve transport to the cytoplasm. Mature RNA binds to them.
The importance of deoxyribonucleic and ribonucleic acids
Nucleic acids are of great importance in the life of organisms. It is stored in them, transferred to the cytoplasm and inherited by daughter cellsinformation about the proteins synthesized in each cell. They are present in all living organisms, the stability of these acids plays an important role for the normal functioning of both cells and the whole organism. Any changes in their structure will lead to cellular changes.
