Ribosomal RNA

3D structure of the 50S subunit Haloarcula marismortui. The proteins are shown in blue, the 23S RNA in orange and the 5S RNA in yellow.

ribosomal ribonucleic acid or ribosomal (rRNA) is an RNA that forms part of ribosomes and is essential for protein synthesis in all living things. rRNAs form the framework of ribosomes and associate with specific proteins to form pre-ribosomal subunits. It is the most predominant material in the ribosome, which by weight consists of approximately 60% rRNA and 40% protein. Ribosomes contain two main types of rRNA that form two subunits: the Large Subunit (LSU, which is a ribozyme that catalyzes the formation of peptide bonds), and the Small Sub Unit (SSU). rRNA is the most abundant type of RNA in cells and is made up of a single strand of nucleotides, although it presents regions of intrastranded double helixes. rRNA sequences are widely used to deduce evolutionary relationships between organisms since they are found in all forms of life.

Prokaryotes vs. Eukaryotes

Both prokaryotic and eukaryotic ribosomes consist of two subunits, but each of these is made up of different types of rRNA. Traditionally, ribosomal RNAs are named according to their sedimentation coefficient, measured in Svedberg (S) units. The following table shows the types of rRNA in two model species: Escherichia coli (prokaryote) and Homo sapiens (eukaryote):

Prokaryotes

In prokaryotes, the larger (50S) subunit is composed of 5S rRNA and 23S rRNA, while the smaller (30S) subunit is composed solely of 16S rRNA. The 3' of the 16S rRNA is the one that binds to the Shine-Dalgarno sequence at the 5' end. of the mRNA. In bacteria, these genes (5S rRNA, 23S rRNA, and 16S rRNA) are typically organized in an operon that is cotranscribed and of which there may be one or more copies. Archaea contain either one rDNA operon or multiple copies.

Eukaryotes

In eukaryotes, the larger (60S) subunit is composed of 5S rRNA, 5.8S rRNA, and 28S rRNA, while the smaller subunit consists of 18S rRNA. Plants have 25S rRNA, unlike the 28S rRNA in mammals.

Eukaryotes generally have many copies of rRNA genes arranged in tandem repeats. In humans, there are 300–400 repeats in 5 clusters (on chromosomes 13, 14, 15, 21, and 22.) Due to their special structure and transcription pattern, rRNA gene clusters are often referred to as 'DNA'. ribosomal (rDNA)” (note that the term does not refer to ribosomes containing DNA).

The tertiary structure of the smaller subunit (SSU rRNA) has been elucidated by X-ray crystallography. major and 3' minor.

Importance of ribosomal RNA

Characteristics of ribosomal RNA are important in evolution, taxonomy, and medicine.

• RNA is one of the only genetic materials present in all cells. For this reason, the genes that encode for RRNA (DNA) are sequenced to identify the taxonomic group to which an organism belongs, infer inter-agency relationships and estimate divergence rates. For this reason, there are specialized databases that store this information, such as RDP-II and SILVA.
• Many antibiotics act influencing RNA: cloranfenicol, erythromycin, paromomycin, ricin, spectinomycin and streptomycin.
• It has been shown that some RNAs are the origin of some microRNAs, such as miR-663 in humans and miR-712 in mouse. These miRNAs arise from internal RNA spacers that are transcribed.