What is RNA?

We explain what RNA is, how is its structure and the different functions it fulfills. In addition, its classification and differences with DNA.

1. What is RNA?

RNA (Ribonucleic Acid) is one of the elementary nucleic acids for life , in charge of DNA synthesis ( protein deoxyribonucleic acid) in the work of protein synthesis and genetic inheritance.

This acid is present inside both prokaryotic and eukaryotic cells , and even as the only genetic material of certain types of viruses (RNA Virus), and consists of a single chain molecule of nucleotides (ribonucleotides) formed in turn for 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 usually a linear and single-chain molecule (single chain), and fulfills a variety of functions within the cell complex , which makes it a versatile executor of the information contained in the DNA.

RNA  was discovered next to DNA in 1867 , by Friedrich MIescher, who called them  nuclein  and isolated them from the cell nucleus , although their existence was also proven in prokaryotic cells, without a nucleus. The mode of RNA synthesis 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 thesis 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 ).

2. RNA structure

Both DNA and RNA are formed by a chain of units known as monomers , which are repeated and called nucleotides; these are linked together by negatively charged phosphodiester bonds. Each of these nucleotides is composed of:

• A monosaccharide sugar molecule called ribose (other than DNA deoxyribose).
• 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 Timina presents 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.
• Secondary . Since the RNA folds on itself due to the intramolecular base pairing, its secondary structure refers to the shape it acquires during folding: in a helix, loop, hairpin loop, bump, pseudo, etc.
• Tertiary . Although RNA does not form a double helix like DNA in its structure, it usually forms a simple helix as a tertiary structure, as its atoms interact with the surrounding space.

3. 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. For this, it goes to the ribosomes, which operate as a kind of molecular protein factory, and it does so following the pattern that the DNA prints on it.

4. RNA types

There are several types of RNA, depending on their primary function:

• Messenger or coding RNA  ( mRNA ) . It deals with copying and carrying the exact amino acid sequence of the DNA to the ribosomes, where the instructions are followed and protein synthesis is carried out.
• 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 new proteins assembled on the mRNA template. They act as well as ribozymes.
• RNA regulators . These are complementary pieces of RNA, in specific regions of the mRNA or of the DNA, that can be used for various tasks: interferences in the replication to suppress specific genes (RNAi), activators of transcription (antisense RNA), or regulate the expression gene (long cRNA).
• RNA catalyst . Pieces of RNA that operate as biocatalysts, operating on the synthesis processes themselves to make them more efficient or ensure their proper development, or even fully implement them.
• Mitochondrial RNA . Since the cell’s mitochondria have their own protein synthesis system, they also have their own forms of DNA and RNA.

5. RNA and DNA

The difference between RNA and DNA is based, first of all, on its constitution: as has been said, the RNA has a nitrogen base different (uracil) from thymine and is composed of a sugar other than deoxyribose (ribose).

Apart from that, DNA has a double helix in its structure , that is, RNA is a more complex and small molecule, which has much less time to live in our cells.

However, their differences are deeper, since DNA serves as an information bank, an orderly pattern of the elementary sequence that allows us to build our body’s proteins; while the ARN is its reader, transcriber and executor : the one in charge of reading the code, interpreting it and materializing it.