Why was the DNA molecule chosen by evolution to store genetic information?
Today, 25 April, on International DNA Day, we look at some of the curiosities about the DNA molecule that have led to its selection as the form of genetic storage and transfer in plants, animals, fungi, archaea and bacteria.
There is a multitude of nucleic acid molecules involved in cellular processes (mRNA, rRNA, tRNA, siRNA, miRNA, etc.), but all of them specialise in temporary roles, acting as intermediaries in protein synthesis, structural components of ribosomes, transport of nucleic acids or regulation of gene expression. On the other hand, DNA, as a molecule, performs the same function of storing and preserving genetic information, suggesting that it is the result of an evolutionary process of specialisation at the molecular level.
The RNA world hypothesis suggests that before DNA and proteins came to dominate life, RNA was the key molecule for storing genetic information and catalysing biochemical reactions. Unlike DNA, RNA can act as both genetic material and an enzyme (ribozyme), which would have allowed it to replicate itself and carry out primitive metabolic functions. Over time, DNA, which is more stable and efficient at storing information, replaced RNA.
What are the structural features that make DNA so stable?
- Double helix structure. DNA has a double-stranded structure that provides mechanical and chemical protection.
- Absence of the hydroxyl group on the pentose. DNA uses deoxyribose as a sugar, whereas RNA uses ribose. Ribose has a hydroxyl group (-OH) on carbon 2′, which makes RNA more reactive and unstable, as it can undergo spontaneous hydrolysis in alkaline solutions.
-
Base pairing and hydrogen bonding. In DNA, the nitrogenous bases are protected within the double helix and stabilised by hydrogen bonds.
-
Resistance to degrading enzymes, environmental stresses and errors in the molecule. Some of these are:
- Base excision repair (BER), which uses DNA glycosylases to remove the damaged base and fill the gap with the correct base.
- Nucleotide excision repair (NER) removes damaged segments of DNA, such as those caused by UV light (thymine dimers) or chemical agents.
- Mismatch Repair (MMR), corrects replication errors such as base mismatches or small insertions/deletions.
- Homologous recombination repair (HR), corrects double-strand breaks using an intact copy of the sequence as a template.
Despite its ubiquity and its discovery as ‘nuclein’ in 1869, we still do not fully understand all of its secondary functions or the functions of much of the genome of living organisms. An example of this is the phenomenon of microchimerism; fetal DNA has been found in the brains of mothers, suggesting a long-lasting biological link between mother and child, and the long-term effects of fetal DNA in the mother and its possible influence on postnatal health are being explored.
The development of new bioinformatics tools, artificial intelligence, database expansion and combination with other omics techniques is the way to further understand the functions of DNA and work on biotechnological applications, from disease prevention to food production or ecological conservation.
At Microomics, we work on the taxonomic and functional information provided by this molecule to understand microbial communities in a variety of niches, as well as physiological processes at the cellular and molecular level, together with other omics information.
What other curiosities about the DNA molecule would you highlight?