The chromosomes are made up of DNA (deoxyribonucleic acid), which encodes the hereditary information, and by histonic and non-histonic proteins. Each chromosome is made up of a single DNA molecule, in which each gene occupies a segment.The DNA is constituted by the association of molecules called nucleotides, formed by the union of a phosphate molecule, one of the deoxyribose sugar and a nitrogen base. Since four different bases, adenine, guanine, thymine and cytosine participate in the formation of nucleotides, there are four different types of these.
To form DNA, nucleotides are linked by their phosphate groups and form a long strand, whose nitrogenous bases are joined by weak but very specific bonds with those of another strand. Thus, base pairs are formed, which determine that both strands, paired, are rolled to give rise to the double helix structure. The unions between the bases only occur, on the one hand, between adenine and thymine and, on the other, between guanine and cytosine, which are therefore called complementary bases.
The inheritance message or genetic code is contained in the order or sequence with which the bases appear in the long strand of the DNA.The genetic message only consists of information that determines the number, type and amino acid sequence of each of the different types of proteins in an organism. The DNA base sequence determines the sequence in which amino acids bind each other to Give rise to a protein.
Central Dogma of Molecular Genetics
The central dogma of molecular genetics was proposed by Crick in 1970. He proposes that there is unidirectionality in the expression of information contained in the genes of a cell, that is, that DNA is transcribed into messenger RNA and that it is translated into protein, an element that finally performs cellular action. Dogma also postulates that only DNA can replicate and, therefore, reproduce and transmit genetic information to offspring. The Retroviridae and Caulimoviridae viruses have the power to synthesize DNA using a polymerase, the reverse transcriptase, which has as its RNA template. This implies a modification of dogma. Another situation that breaks with the sequence defined by dogma is the possibility of obtaining protein in vitro, in a cell-free system and in the absence of RNA,
- Replication, in which the parent DNA is copied to form daughter DNA molecules whose nucleotide sequences are identical to those of the paternal DNA.
- Transcription is the process by which part of the genetic message of DNA in the form of RNA is transcribed.
- The translation, in which the genetic message encoded by the RNA is deciphered in the ribosomes in the 20-letter alphabet of the protein structure.
After several discoveries, this dogma has been expanded:
- Reverse transcription, or flow of genetic information from RNA to DNA (discovery of reverse transcriptases).
- RNA replication (discovery of replicases).