The time in which we live is marked by tremendous changes, tremendous progress, when people get answers to more and more new questions. Life is rapidly moving forward, and what until recently seemed impossible is beginning to be put into practice. It is entirely possible that what appears to be a plot from the genre of fiction today will soon also acquire features of reality.
One of the most important discoveries in the second half of the twentieth century was the nucleic acids of RNA and DNA, thanks to which a person came closer to the mysteries of nature.
Nucleic acids
Nucleic acids are organic compounds with high molecular weight properties. They include hydrogen, carbon, nitrogen and phosphorus.
They were discovered in 1869 by F. Misher, who examined pus. However, then its discovery was not given much importance. Only later, when these acids were found in all animal and plant cells, the understanding of their enormous role came.
There are two types of nucleic acids: RNA and DNA (ribonucleic and deoxyribonucleic acids). This article is devoted to ribonucleic acid, but for a general understanding, we also consider what DNA is.
What is deoxyribonucleic acid?
DNA is a nucleic acid consisting of two strands, which are connected according to the law of complementarity with 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 the 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 DNA structure contains all the genetic information. DNA has replication, which means a process in which two completely identical, daughter, are formed from one molecule.
As already noted, the chain consists 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. A hydrogen bond does not occur between all bases, adenine, for example, can only be combined 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 ones (Chargeff'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 the two chains are arranged in an orderly manner, and also selectively combine, is called the principle of complementarity. In addition to hydrogen compounds, the double helix also interacts hydrophobically.
Two chains are oppositely directed, that is, located in opposite directions. Therefore, opposite the three'-end of one is the five'-end of the other chain.
Externally , the DNA molecule resembles a spiral staircase, the railing of which is the sugar phosphate backbone, and the steps are complementary bases of nitrogen.
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 phosphated N-glycoside, which is built on the residue of pentose (five-carbon sugar), with a phosphate group of the fifth carbon atom and nitrogen base at the first carbon atom.
It is a single polynucleotide chain (except viruses), which is much shorter than that of DNA.
One RNA monomer is the remains of the following substances:
- nitrogen bases;
- five-carbon monosaccharide;
- phosphorus acid.
RNAs have pyrimidine (uracil and cytosine) and purine (adenine, guanine) bases. Ribose is a monosaccharide of an RNA nucleotide.
Differences between RNA and DNA
Nucleic acids differ from each other in the following properties:
- its amount in the cell depends on the physiological state, age and organ affiliation;
- DNA contains carbohydrate deoxyribose, and RNA contains ribose;
- the nitrogenous base of DNA is thymine, and that of RNA is uracil;
- classes perform various functions, but are synthesized on a DNA matrix;
- DNA consists of a double helix, and RNA consists of a single chain;
- Chargeff’s rules for DNA are uncharacteristic for her;
- RNA has more minor bases;
- chains vary significantly in length.
Study history
An RNA cell was first discovered by a German biochemist R. Altman in a study of yeast cells. In the mid-twentieth century, the role of DNA in genetics was proven. Only then did RNA types, functions, and so on be described. Up to 80-90% of the mass in the cell falls on r-RNA, which together with proteins form ribosomes and participate in protein biosynthesis.
In the sixties of the last century, it was first suggested that there must be some kind 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 for detecting the nucleotide sequence began to be developed and the structure of RNA in the acid space was established. So it was found that some of them, which were called ribozymes, can cleave polyribonucleotide chains. As a result, they began to assume that at the time when life was emerging on the planet, RNA acted without DNA and proteins. Moreover, all the transformations were made with her participation.
The structure of the molecule of ribonucleic acid
Almost all RNAs are single chains of polynucleotides, which, in turn, are composed 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 interconnected by three- and five-phosphodiester bonds.
A very different 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.
The structure of the molecule of ribnucleic acid
As already mentioned, the molecule has a single-stranded structure. RNA receives a secondary structure and shape as a result of the interaction of nucleotides with each other. This is a polymer whose monomer is a nucleotide consisting of sugar, a phosphorus acid residue and a nitrogen base. Externally, the molecule is similar to one of the DNA chains. The nucleotides adenine and guanine, which are part of the RNA, are purine. Cytosine and uracil are pyrimidine bases.
Synthesis process
For the RNA molecule to be synthesized, the matrix is a DNA molecule. True, there is an inverse process, when new molecules of deoxyribonucleic acid are formed on the ribonucleic acid matrix. This occurs during the replication of certain types of viruses.
Other ribonucleic acid molecules can also serve as a basis for biosynthesis. Its transcription, which occurs in the cell nucleus, involves many enzymes, but the most significant of these is RNA polymerase.
Kinds
Depending on the type of RNA, its functions also differ. There are several types:
- informational i-RNA;
- ribosomal r-RNA;
- 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 nuclei on DNA matrices, then passing into the cytoplasm and binding to ribosomes. Further, they become matrices for protein synthesis: they are joined by transport RNAs that carry amino acids. This is the process of converting information that is implemented in a unique protein structure. In some viral RNAs, it is also a chromosome.
Jacob and Mano are the discoverers of this species. Without a rigid structure, its chain forms curved loops. Without working, the i-RNA folds and folds into a ball, and in the working state unfolds.
i-RNA carries information about the sequence of amino acids in a protein that is synthesized. Each amino acid is encoded in a specific place using genetic codes, which are characteristic of:
- tripletness - out of four mononucleotides it is possible to build sixty-four codons (genetic code);
- non-overlap - information moves in one direction;
- continuity - the principle of operation is that one i-RNA is one protein;
- universality - this or that type of amino acid is encoded equally in all living organisms;
- degeneracy - twenty amino acids are known, and codons are sixty-one, that is, they are encoded by several genetic codes.
Ribosomal Ribonucleic Acid
Such molecules make up the vast majority of cellular RNA, namely from eighty to ninety percent of the total. They combine with proteins and form ribosomes - these are organoids that perform protein synthesis.
Ribosomes are sixty-five percent of r-RNA and thirty-five percent of protein. This polynucleotide chain easily bends with the protein.
The ribosome consists of amino acid and peptide sites. They are located on 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 i-RNA, 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. In this case, amino acids are transported by transport molecules. However, it happens that an amino acid is encoded by different codons. Then several transport RNAs will carry them.
It folds into a glomerulus when inactive, and when functioning, it looks like a clover leaf.
The following sections are distinguished in it:
- an acceptor stem having an ACC nucleotide sequence;
- a site serving to attach to the ribosome;
- anticodon encoding the amino acid that is attached to this t-RNA.
Minor view of ribonucleic acid
Recently, RNA species has replenished with a new class, the so-called small RNAs. Most likely, they are universal regulators that turn genes on or off in embryonic development, as well as control the processes inside the cells.
Ribozymes are also recently identified, they are actively involved when the RNA acid is fermented, being a catalyst.
Viral types of acids
The virus is capable of containing either ribonucleic acid or deoxyribonucleic acid. Therefore, with the corresponding molecules, they are called RNA-containing. When such a virus enters the cell, reverse transcription occurs - on the basis of ribonucleic acid, new DNA appears that integrate into the cells, ensuring the existence and reproduction of the virus. In another case, complementary RNA formation occurs. Protein viruses, vital activity and reproduction are without DNA, but only on the basis of information contained in the RNA of the virus.
Replication
In order to improve general understanding, it is necessary to consider the replication process, as a result of which two identical nucleic acid molecules appear. So 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 maternal DNA, capturing the whole molecule;
- the breaking of hydrogen bonds, in which the chains diverge, and a replicative fork appears;
- adjustment of DNTF to the freed bases of mother chains;
- the removal of pyrophosphates from dNTP molecules and the formation of phosphodiester bonds due to the released energy;
- respiration.
After the formation of a daughter molecule, the nucleus, cytoplasm, and the rest divide. Thus, two daughter cells are formed that completely receive all the genetic information.
In addition, the primary structure of the proteins that are synthesized in the cell is encoded. DNA in this process takes an indirect part, and not a direct one, consisting in the fact that it is the DNA that synthesizes involved in the formation of proteins, RNA. 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 in some respects similar to replication, while in others it differs significantly from it.
The similarities are the following parts:
- the beginning goes with DNA despiralization;
- hydrogen bonds between chain bases break;
- NTFs are complementary to them;
- the formation of hydrogen bonds occurs.
Differences from replication:
- during transcription, only a portion of the DNA corresponding to the transcript is unwoven, while during replication the whole molecule is untwisted;
- during transcription, adaptive NTPs contain ribose, and uracil instead of thymine;
- information is written off only from a certain site;
- after the formation of the molecule, the hydrogen bonds and the synthesized chain are broken, and the chain slides off the DNA.
For normal functioning, the primary structure of RNA should consist only of DNA sections written off from exons.
In newly formed RNA, the maturation process begins. Silent sections are cut out, and informative ones are sewn together, forming a polynucleotide chain. Further, each species has transformations inherent only to it.
In i-RNA, attachment to the initial end occurs. Polyadenylate is attached to the final site.
In t-RNA, bases are modified to form minor species.
Separate bases are also methylated for r-RNA.
Protect from destruction and improve the transport of proteins into the cytoplasm. Mature RNAs bind to them.
The value of deoxyribonucleic and ribonucleic acids
Nucleic acids are of great importance in the life of organisms. They store, transfer to the cytoplasm and pass on the inheritance to daughter cells information about proteins synthesized in each cell. They are present in all living organisms, the stability of these acids plays a crucial role for the normal functioning of both cells and the whole organism. Any changes in their structure will lead to cellular changes.