We explain what RNA is, what its structure is like and the different functions it performs. Also, its classification and differences with DNA.
What is RNA?
RNA (Ribonucleic Acid) is one of the elemental nucleic acids for life, in charge, together with DNA (deoxyribonucleic acid), of the protein synthesis and genetic inheritance tasks.
This acid is present inside both prokaryotic and eukaryotic cells, and even as the only genetic material of certain types of viruses (RNA viruses), and consists of a molecule in the form of a single chain of nucleotides (ribonucleotides) formed in turn by a sugar (ribose), a phosphate and one of the four nitrogenous bases that make up the genetic code: adenine, guanine, cytosine or uracil.
It is generally a linear and single-stranded (single-stranded) molecule, and fulfills a variety of functions within the complex of the cell, which makes it a versatile executor of the information contained in DNA.
RNA was discovered along with DNA in 1867, by Friedrich MIescher, who called them nuclein and isolated them from the cell nucleus, although their existence was also later proven in prokaryotic cells, without a nucleus. The mode of synthesis of RNA in the cell was later discovered by the Spanish Severo Ochoa Albornoz, winner of the Nobel Prize in Medicine in 1959.
The understanding of how RNA operates and its importance for life and evolution, made possible the emergence of theses on the origin of life, such as the one that intuits in 2016 that the molecules of this nucleic acid were the first forms of life in exist (in the RNA world Hypothesis).
RNA structure
Both DNA and RNA are made up of a chain of units known as monomers, which are repeated and are called nucleotides; These are linked together by negatively charged phosphodiester bonds. Each of these nucleotides is made up of:
- A monosaccharide sugar molecule called ribose (other than deoxyribose in DNA).
- A phosphate group (salts or esters of phosphoric acid).
- A nitrogenous base: Adenine, Guanine, Cytosine or Uracil (in the latter it differs from DNA, which has Thymine instead of Uracil).
These components are organized based on three structural levels, which are:
- Primary. The linear sequence of nucleotides that define the following structures.
- High school. Since RNA folds on itself due to intramolecular base pairing, its secondary structure refers to the shape it takes during folding: helix, loop, hairpin loop, bulge, pseudo-knot, etc.
- Tertiary. Although RNA does not form a double helix like DNA in its structure, it does tend to form a single helix as a tertiary structure, as its atoms interact with the surrounding space.
RNA function
RNA fulfills numerous functions, the most important being protein synthesis, in which it copies the genetic order contained in the DNA to use it as a standard in the manufacture of proteins and enzymes and various substances necessary for the cell and the organism. To do this, it goes to the ribosomes, which operate as a kind of molecular protein factory, and it does so by following the pattern printed by DNA.
RNA types
There are several types of RNA, depending on their primary function:
- Messenger or coding RNA (mRNA). It is responsible for copying and carrying the exact sequence of amino acids from DNA to the ribosomes, where instructions are followed and proteins are synthesized.
- Transfer RNA (tRNA). These are short polymers of 80 nucleotides that have the mission of transferring the pattern copied by the mRNA to the ribosomal RNA, serving as an assembly machine, choosing the correct amino acids based on the genetic code.
- Ribosomal RNA (rRNA). Its name comes from the fact that it is found in the ribosomes of the cell, where they are combined with other proteins. They operate as catalytic components to “weld” the newly assembled proteins onto the mRNA template. They act, thus, as ribozymes.
- Regulatory RNAs. They are complementary pieces of RNA, in specific regions of mRNA or DNA, that can perform various tasks: interference in replication to suppress specific genes (RNAi), activators of transcription (antisense RNA), or regulate expression gene (long cRNA).
- Catalyst RNA. Pieces of RNA that operate as biocatalysts, operating on the synthesis processes themselves to make them more efficient or ensure their correct development, or even put them fully into operation.
- Mitochondrial RNA. Since the cell’s mitochondria have their own protein synthesis system, they also have their own forms of DNA and RNA.
RNA and DNA
The difference between RNA and DNA is based, first of all, on their constitution: as has been said, RNA has a different nitrogen base (uracil) than thymine and is composed of a different sugar than deoxyribose (ribose).
Apart from that, DNA has a double helix in its structureIn other words, RNA is a smaller and more complex molecule, which has a much shorter life span in our cells.
However, their differences are more profound, since DNA serves as a bank of information, an ordered pattern of the elemental sequence that allows us to build the proteins in our body; while RNA is its reader, transcriber and executor: the person in charge of reading the code, interpreting it and materializing it.