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 basic nucleic acids for life responsible together with DNA (deoxyribonucleic acid) for the tasks 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 Viruses). It consists of a molecule in the form of a simple 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, single-stranded molecule, and it fulfills a variety of functions within the cell, making it a versatile executor of the information contained in DNA.
The RNA It was discovered together with DNA in 1867 by Friedrich Miescher, who called them nuclein and isolated them from the cell nucleus, although later 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.
Understanding how RNA operates and what its importance is for life and evolution allowed the emergence of various theses on the origin of life, such as the one that suggests that the molecules of this nucleic acid were the first forms of life to exist (in the RNA World Hypothesis).
See also: Bacteria
RNA structure
Both DNA and RNA are made up of a chain of units known as monomers which repeat and are called nucleotides. The nucleotides are linked together by negatively charged phosphodiester bonds. Each of these nucleotides is made up of:
- A pentose (5-carbon sugar) sugar molecule called ribose (different from the 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:
- Primary level. It consists of the linear sequence of nucleotides that define the following structures.
- Secondary level. RNA folds back on itself due to intramolecular base pairing. The secondary structure is the shape it acquires during folding: helix, loop, hairpin loop, multiple loop, internal loop, protuberance, pseudoknot, etc.
- Tertiary level. Although RNA does not form a double helix like DNA in its structure, it usually forms a single helix as a tertiary structure, as its atoms interact with the surrounding space.
RNA function
RNA fulfills numerous functions. The most important is protein synthesis, in which it copies the genetic order contained in DNA to use it as a template in the manufacture of proteins and enzymes and various substances necessary for the cell and the organism. To do this, it uses ribosomes, which operate as a kind of molecular protein factory, and it does so following the pattern printed by the DNA.
Types of RNA
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 the instructions are followed and protein synthesis proceeds.
- transfer RNA (tRNA). These are short polymers of 80 nucleotides, which have the mission of transferring amino acids to the ribosomes, which will act as assembly machines, ordering the correct amino acids along the messenger RNA (mRNA) molecule based on the genetic code.
- ribosomal RNA (rRNA). They are found on the cell's ribosomes, where they are combined with other proteins. They operate as catalytic components to “weld” the peptide bonds between the amino acids of the new protein that is being synthesized. Thus, they act as ribozymes.
- regulatory RNAs. They are complementary pieces of RNA located in specific regions of the mRNA or DNA, and that can perform various tasks: interfering with replication to suppress specific genes (RNAi), inhibiting transcription (antisense RNA), or regulating gene expression (ncRNA). long).
- catalyst RNA. They are pieces of RNA that operate as biocatalysts on the synthesis processes themselves to make them more efficient. In addition, they ensure the correct development of these processes.
- 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: RNA has a nitrogenous base (uracil) other than thymine and is made up of a sugar other than deoxyribose (ribose).
Besides, DNA has a double helix in its structure that is, it is a more complex and stable molecule. RNA is a simpler and smaller molecule that has a much shorter lifespan in our cells.
DNA serves as an information bank: it is an ordered pattern of the elemental sequence that allows us to build our body's proteins. RNA is its reader, transcriber and executor: the person in charge of reading the code, interpreting it and materializing it.
Continue with: Structure of DNA
References
- Biology: Solomon E., Berg L., Martin D. (2013) 9th Edition. Cengage Learning Publishing.
- Cellular and Molecular Biology. From Robertis Edward, Hib José. (2012) 16th ed. Promed Editorial.
