We explain what DNA is and why it is essential for life. Structure, DNA replication and differences between DNA and RNA.
DNA also has a double helix shape, coiled on itself.What is DNA?
DNA or deoxyribonucleic acid is a polymer essential for life, found inside all cells of the living beings and inside most virus. It is a complex, long protein, inside which all the genetic information of the individual is stored, that is, the instructions for the synthesis of all the proteins that make up its organism: it could be said that it contains the molecular instructions for the assembly of a living being.
The smallest units of such genetic information are called genes and they consist of a specific sequence of nucleotides that make up DNA, and also allow their hereditary transmission, something vital for the evolution of life. Also, in these structures information is also contained regarding how and when the synthesis of the basic components of the cells should occur.
DNA is contained in cells, either dispersed throughout their cytoplasm (in the case of organisms prokaryotes: bacteria and archaea) and or within the cell nucleus (in the case of eukaryotes: floors, animals, mushrooms). For its decoding and use as a template, the intervention of RNA or ribonucleic acid is required, which reads the structure and uses it as a template, in a process called transcription/translation.
It must be said that the DNA of each individual is unique and different, the product of the combination of the genetic codes of their parents in a process that occurs at random. This, of course, in the organisms of sexual reproduction, in which each progenitor contributes half of its genome to make a new individual. In the case of unicellular organisms of asexual reproduction, the molecule of DNA reproduces itself in a process called replication.
The genetic content of DNA is extremely valuable for life, and despite this it is possible that it suffers damage due to contact with mutagens: ionizing radiation, certain chemical elements or even some drugs (as in the case of chemotherapy), which would lead to transcription errors during cell synthesis. This can lead to disease and death of the individual, or also to the hereditary transmission of defective structures, giving rise to descendants with congenital defects.
DNA structure
The DNA molecule is a long string of units called nucleotides, which in turn consist of a sugar molecule (in this case deoxyribose: C5H10O4), a nitrogenous base (which can be adenine, guanine, cytosine or thymine), and a group phosphate that serves as a bond between nucleotides. Hence, each nucleotide is distinguished from the others in the nitrogenous base it possesses, and that all together they make a chain called DNA sequence and that can be transcribed using the initial of each base, for example: ACTAGTCAGT…
DNA also has a double helix shape, coiled on itself in three different patterns (called A, B and Z), according to its sequence, number of bases and specific function. This structure is produced due to the union of two strands of nucleotides by means of hydrogen bonds.
Replication of DNA
Replication is the process by which a DNA molecule generates two identical to itself, and is key in the cell reproduction, since all the cells of the body must have the same exact genome (as in asexually reproducing organisms, which are practically clones of each other).
The process consists of the separation of the two DNA strands, each of which will function as a template to synthesize a new partner. If all goes well, in the end there will be two identical molecules of the original DNA, both in a double helix. Hence, replication is key to inheritance.
Three types of DNA replication are assumed:
- Semiconservative. As described above, the strands separate and from each of the old ones a new one is synthesized.
- Conservative. It would take place if the two old strands, after serving as a template, came back together with their old partner and in the end there was an entirely new DNA molecule, next to the old one that would be reconstituted.
- Dispersive. It would happen if the resulting helices were made up of fragments of the old and new DNA.
Differences between DNA and RNA
The DNA and the RNA they are chains of similar nucleotides, but they differ, as their name indicates, in the type of sugar present in their structure: deoxyribose and ribose, respectively.
Furthermore, RNA is almost four times larger than DNA, and is made up of one single helix, rather than two. This distinction is also functional, obviously, since DNA contains the genetic template and RNA is responsible for executing or transporting it.