What Is DNA? Its Characteristics, Parts And Functions
DNA is probably the best-known molecule of biological origin , this is found in all living beings on planet Earth. But… Why is DNA so important?
DNA (deoxyribonucleic acid) contains the instructions necessary for life: within our DNA is encoded the information necessary to make all the proteins in our body. Proteins fulfill a multitude of roles, determining the structure of cells and directing almost all metabolic processes in the body.
Differences in the genetic code are responsible for a multitude of phenomena that we observe in humans and animals: for example, why some people are more likely than others to develop certain diseases, or why dogs have tails, different colors of eyes or blood group. All our physical and psychological traits are determined by genetics, although the environment can significantly influence our development.
We have all heard about DNA and know its fundamental role in our body as the guardian of genetic information, but… Are there other functions? In this article we talk in depth about DNA, its structure and all its functions
DNA is the acronym used for deoxyribonucleic acid. We can say that DNA is the building block of all living things, contains all genes necessary for the manufacture of proteins, molecules essential for the functioning of our body.
DNA contains our inherited material, which makes us who we are, no person has the same DNA as another: each person has a unique code contained in the long DNA molecule. The information contained in DNA is passed from parents to children and approximately half of a child’s DNA is of paternal origin and the other half is maternal.
DNA structure
DNA is described as a polymer of nucleotides, that is, a long chain made up of small molecules
Nucleotides are the fundamental units of deoxyribonucleic acid (DNA). Each nucleotide can be divided into three parts: a carbohydrate (2-deoxyribose), a nitrogenous base and a phosphate group (derived from phosphoric acid).
Nucleotides are distinguished by their nitrogenous base , and it is the name of the base that is specified when presenting the DNA sequence, since the two other components are always the same. There are four different bases:
DNA takes the shape of a double helix, when viewed on a three-dimensional level; It is made up of two chains held together by hydrogen bonds , forming a double-stranded molecule. The base pairs form the ladder-like spiral, and the sugar phosphate backbone forms the supporting sides of the DNA helix.
The bases are aligned in sequential order along the chain, encoding the genetic information according to the criterion of complementarity: AT and GC. The size of adenine and guanine is larger than that of thymine and cytosine, making this complementarity criterion necessary for DNA to remain uniform.
On the other hand, DNA is found in the cell nucleus of eukaryotes, as well as in chloroplasts and mitochondria In prokaryotic organisms, the molecule is free in the cytoplasm in an irregularly shaped body known as a nucleoid. Finally, it must be added that the structure of DNA differs between prokaryotic and eukaryotic cells. In eukaryotic cells it has a linear structure, and the ends of each chain are free; However, in prokaryotic cells DNA is contained in a long, circular double strand.
What is DNA used for?
DNA has three main functions in the body : store information (genes and entire genome), produce proteins (transcription and translation) and replicate to ensure that information is passed on to daughter cells during cell division.
The information needed to build and maintain an organism is stored in DNA, which is passed from parent to child. The DNA that carries this information is called genomic DNA, and the set of genetic information is called the genome. We have more than two meters of DNA, and our nuclei are much smaller : DNA is organized into compact molecules called chromatin, which correspond to the association of DNA, RNA and proteins. The chromatin is then assembled into chromosomes, highly organized structures that allow cell divisions.
The categories and parts of DNA
DNA can be divided into two broad categories: non-coding DNA and coding DNA. Let’s look at its specific functions.
1. Coding DNA
We cannot talk about coding DNA without talking about genes. A gene is a section of DNA that influences a trait or characteristic of an organism , such as eye color or blood type. Genes have coding regions called open reading frames, as well as control sections called enhancers and promoters that influence the coding region to be transcribed. The total amount of information contained in an organism’s genome is called the genotype.
DNA has the information for the manufacture of proteins, which are called the workers of the organism, and which fulfill a multitude of functions; Some proteins are structural, such as hair or cartilage proteins, while others are functional, such as enzymes.
The body uses 20 different amino acids to make approximately 30,000 different proteins The DNA molecule has to tell the cell the order in which the amino acids should join together.
Heredity determines which proteins will be produced, using DNA as a blueprint to build them. Sometimes changes to the DNA code (mutations) will cause proteins to not work properly, causing disease. However, at other times code changes will cause beneficial alterations in individuals, who will then be able to better adapt to their environment.
A gene has DNA that is read and converted into an RNA messenger substance. This RNA transmits information between the DNA of the gene and the machinery responsible for making proteins RNA acts as a blueprint for the production machinery, so amino acids are arranged and connected in the correct order to produce a protein.
Although transcription into proteins is the basic role of DNA. The central dogma of biology DNA → RNA → protein has been shown to be wrong and, in fact, there are multiple processes that influence and transfer information. Some viruses use RNA as their parent material (RNA viruses), and The process of information flowing from RNA to DNA is known as reverse transcription or reverse transcription DNA There are also non-coding RNA sequences that are created by transferring DNA sequences into RNA, and these can have a function without becoming proteins.
Related article: “What is the genetic code and how does it work?”
2. Non-coding DNA
Approximately 90% of a person’s genome does not code for proteins This part of DNA is called non-coding DNA. DNA can be conceptually divided into two categories, protein-coding genes and non-genes. In many species, only a small portion of the DNA encodes proteins – the exons – and they only make up about 1.5% of the human genome.
Non-coding DNA, also known as junk DNA, is DNA that does not code for a protein: sequences such as introns, virus recombinations, etc. Until recently it was thought that this DNA was useless until recent studies showed that this is not the case. These sequences can regulate gene expression as they have an affinity for proteins that can bind DNA and are called regulatory sequences.
Scientists have only identified a small percentage of the total existing regulatory sequences The reason for the presence of large amounts of non-coding DNA in eukaryotic genomes and the differences in genome size between different species remains an enigma today. Although more and more functions of non-coding DNA are known, such as:
Repetitive elements in a genome are also functional parts of a genome, They make up more than half of the total nucleotides A group of scientists at Yale University recently found a non-coding DNA sequence that supposedly plays a role in allowing humans to develop the ability to use tools.
2.2. Telomeres and Centromeres
Additionally, some DNA sequences are responsible for the structure of chromosomes. Telomeres and centromeres contain few or no coding genes, but They are crucial for holding the chromosome structure together
23. DNA to RNA
Some genes do not code for proteins, but are transcribed into RNA molecules: ribosomal RNA, transfer RNA, and RNA interference (RNAi).
2.4. Alternative splicing
The arrangement of introns and exons in some gene sequences is important because allows alternative splicing of pre-messenger RNA , creating different proteins from the same gene. Without this ability, the immune system would not exist.
2.5. Pseudogenes
Some non-coding DNA sequences come from genes that have been lost in the course of evolution These pseudogenes can be useful because they can give rise to new genes with new functions.
2.6. Small sections of DNA
Other non-coding DNA sequences come from the replication of small sections of DNA, which is also useful because tracking these repetitive sections of DNA can help with phylogeny studies.
Conclusion
DNA is the molecule that contains hereditary information in humans; This information, contained in DNA, allows the cell to know the order in which the amino acids that form proteins should be joined. Proteins are responsible for most of the body’s functions and a problem in their manufacture can have great consequences on our health. However, when we talk about DNA → RNA → protein, we refer to the great dogma of biology and genes, forgetting 90% of DNA. Until recently, the role of DNA, which does not code for a protein, was considered useless, but recent studies have been discovering more and more functions of these non-coding sequences called regulators.
