The typology of DNA depends on its location, functionality and organism that presents it. Let’s see how the molecule is classified from the genetic material of living things.
DNA is the double helix polymer that conditions life. In the form of bound and ordered nucleotides, this molecule presents the necessary instructions for protein synthesis by the cell. If we take into account that protein molecules make up 80% of cellular protoplasm and that every living thing has at least one cell, it will not be difficult for us to recognize that, without DNA, life is completely impossible.
Through transcription and translation processes, DNA nucleotide triplets are “transcribed” into messenger RNA strands, which can travel out of the nucleus to the cell’s cytoplasm. Here, ribosomes “translate” each triplet of nucleotides (codons) from messenger RNA into an amino acid that, chained to others, gives rise to the proteins themselves.
With this mechanism so intricate when analyzed thoroughly and easy to understand in broad strokes, our genome is transformed into life. Now that we are clear about the function of this essential biopolymer, we candedicate this space to knowing the types of DNA and their characteristics. Don’t miss it.
- We recommend you read: “The 7 differences between DNA and RNA”
How is DNA classified?
However many differences exist between the DNA molecules of living beings, they all have something in common: they are composed of nucleotides. A nucleotide can be defined as an organic molecule formed by the covalent bond of a nucleoside (sugar of 5 carbon atoms + nitrogenous base) and a phosphate group.
In the case of DNA, pentose is a deoxyribose (hence the name “deoxyribonucleic acid”), and what defines the nature of each of the deoxyribonucleotides is the nitrogenous base that forms them. On this occasion, the bases can be adenine (A), cytosine (C), guanine (G) and thymine (T), while in RNA thymine is replaced by uracil (U).
If we have the following scheme as an example, we can draw a series of conclusions:
- GCU, GCC, GCA, GCG → Alanine (Wing)
These strange terms refer to triplets or messenger RNA codons that, as we have said, are direct translations of the genes present in nuclear DNA. In this particular case, 4 different combinations of nucleotides encode the synthesis of alanine, an amino acid essential for protein synthesis. Each of them, read by the chromosome, will bring an alanine amino acid to the assembly machinery. The 4 codons are interchangeable, as they have the same function in this process.
With this small express lesson in genetics, we have told you what you need to know to understand everything about the types of DNA that we are going to show you next. We are facing the same molecule, but according to its functionality, certain distinctions can be established.
1. Coding DNA
Coding DNA sequences are those thatcontain the nucleotides necessary for the previously described transcription and translation mechanisms. In other words, the sections of DNA that encode proteins or RNA are genes, of which humans contain about 20,000-25,000.
It should be noted that, in each somatic cell of the human being, humans present a copy of each gene (or two different alleles, if you prefer, which is the most appropriate term). One allele comes from the mother and another from the father, a condition known as diploidy (2n). If one of the parental alleles fails, it is expected that the other can solve the resulting deficiencies.
2. Non-coding DNA
As the name suggests, these sections of nuclear DNA do not code for specific proteins, that is, they are outside the genes. Surprisingly, the human being has 70% extragenic genome and 30% related to genes, with only 1.5% of the truly coding portions.
Until not long ago, coding DNA was related to the term “thrash DNA”, because it was not believed to have any kind of use. Today, the field of epigenetics has burst into the field of science by testing this erroneous preconception. In 2012, the ENCODE project demonstrated that at least 80% of human DNA has biochemical activity, whether or not it is part of specific genes.
Based on epigenetic studies, it has been shown that there are certain regions of the genome capable of activating or inhibiting the expression of certain genes throughout the individual’s life. Thus, although non-coding DNA seems useless to the naked eye, it could explain many long-term clinical events if studied enough.
3. Nuclear DNA
We changed the focus a bit, because in this case we do not rely on functionality only to distinguish the types of DNA, but on their location. Nuclear DNA, as you may have guessed, is thatwhich is located within the nucleus of the cell.
Within the nuclear membrane, DNA is organized into chromosomes, highly organized genetic structures that also contain proteins inside. Each chromosome is made up of two halves (chromatids) and, in turn, they pair in pairs during meiosis to result in the crossover of genetic information.
4. Mitochondrial DNA
Mitochondria, organelles in the cell cytoplasm responsible for supplying almost all the energy to the cell in the form of ATP, contain a small circular chromosome inside. Mitochondria are only inherited from the mother and, therefore, mitochondrial DNA only contains genetic information about her, unlike nuclear DNA.
This DNA is small and circular. To give you an idea, it only contains about 16,500 base pairs, compared to the 3.2 billion present in the chromosomes of the nucleus. However, this tiny genome encodes some of the proteins needed for mitochondria, so it’s vital for human survival.
5. Bacterial DNA
Bacterial DNA is very similar to mitochondrial, saving distances: it consists of a double strand of DNA presented in a circular chromosome on the cytoplasm, without a specific nuclear membrane. During binary fission, this chromosome duplicates and the body of the bacterium splits, giving rise to two genetically identical individuals where there was once one.
The fact that mitochondrial and bacterial DNA are so similar is no coincidence. According to the theory of endosymbiosis, postulated by Lynn Margulis in the book On the origin of mitosing cells (1967), mitochondria and chloroplasts could come from bacterial ancestors, which were phagocytosed by a eukaryotic cell in ancient times and began to be part of it, losing genetic information in the process and adapting to its host.
6. Viral DNA
Not all viruses have DNA, because they do not even have a cellular structure as such. They lack organelles, plasma membrane, cytoplasm and everything else you can think of that defines a cell: they are, simply, strands of DNA or RNA covered by a protein capsid. Therefore, today it is impossible to consider them as living beings, but rather something similar to “biological agents”.
DNA viruses can present from one to several strands, which are organized in a single-stranded, double-stranded, linear or circular way. Because they lack the necessary replication machinery, viruses must necessarily “hijack” host cells in order to replicate their own genetic information.
Summary
We know that there are other types of DNA according to the organization of their chains (DNA B, A and Z), but type B is practically the only one that occurs in living beings. The interest of this categorization is purely scientific, since concrete experimental conditions are required to give rise to type A and Z organizations.
Therefore, we have decided to take a multidisciplinary approach to tell you the types of DNA. The first 4 are present within humans (in coding and non-coding regions, in the nucleus and in mitochondria), while the remaining two variants are unique to microorganisms, whether bacteria or viruses. If something is clear to us after reading these lines, it is that, indeed, without DNA there is no life.
To the classic question “what do you do?” I always answer “basically I am a psychologist”. In fact, my academic training has revolved around the psychology of development, education and community, a field of study influenced my volunteer activities, as well as my first work experiences in personal services.