Ribosomal RNA (rRNA): Function, Definition, and Structure

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What is Ribosomal RNA (rRNA)?

Ribosomal ribonucleic acid is one of the types of non-coding RNA which is one of the primary components in the ribosomes, and it is also very important for all the cells.

rRNA is also known as ribozyme that carries out a protein synthesis in the cell organelle ribosomes, this ribosomal RNA is transcribed from the ribosomal DNA and then it is bound to the ribosomal proteins and forms small and large subunits of the ribosomes.

rRNA is considered as a physical and a mechanical factor for the ribosome as it forces the transfer of RNA and the mRNA which further process and translates into proteins.

Ribosomal RNA is the predominant form of RNA found in most of the cells and it also makes about eighty percentage of the cellular RNA despites never been translated into the proteins by itself.

Ribosomes are made up of approximately 60% of the rRNA and 40% of the other ribosomal protein mass.

Ribosomal RNA (rRNA) molecule in the cells that forms part of the proteins synthesizing organelle which is known ribosome which exported to the cytoplasm of the cells which helps in translating the information in the messenger RNA as protein.

Features of Ribosomal RNA (rRNA)

Ribosomal ribo nucleic acid which is generally referred to as rRNA is the component of the ribosomes, the molecular machines which catalyzes the synthesis of proteins.

rRNA constitutes about six percentage of the ribosomes by weight and are very crucial in performing their functions, such as binding to the mRNA and recruiting the tRNA in catalyzing the formation of the peptide bond in between the two amino acids.

Though the structure od a ribosome is determined by a three-dimensional shape in its rRNA core. Proteins which are present in the ribosomes serves in stabling the structure by interacting with its core.

Ribosomal RNA is transcribed within the nucleus and particularly in the nucleoli which is present inside the nucleus.

They are usually dense, spherical shape which is formed around the loci of the genome and codes for rRNA. Nucleoli are also stable in biogenies of the ribosomes by sequestration of ribosomal proteins.

Discovery of Ribosomal RNA (rRNA)

The Ribosomal RNA was first discovered during the fractionation of the cell experiments which invests the role of RNA viruses which causes cancer.

Fractionation is a method where cell membranes carefully removed in a selective manner by keeping the cellular organelles function intact.

This type of homogenized cytoplasm is further centrifuged at an increasing speed so that the organelles are separated according to the density.

The initial experiments which reveal the presence of rRNA are extracted as a fracted which was thought to represent a new organelle, which is sub-cellular known as microsome – specialized in protein synthesis.

Further it was observed that if the presence of the ribosomes in the endoplasmic reticulum helps in detecting the samples of RNA.

As ribosomal subunits and the rRNA were detected initially by differential centrifugation they are still characterized by their rate of sedimentation with the help of Svedberg coefficient.

As these are not the direct measures of the molecular weight the coefficients are not added directly.

Considering an example of prokaryotic ribosomes where it has a larger subunits 50S and a smaller subunit of 30S comes together as a complex and has a Svedberg co efficient of 70S.

Types of Ribosomal RNA (rRNA)

Both prokaryotic and eukaryotic ribosomes are made up of larger and a smaller sub unit and these units come together during the translation of mRNA.

Where as the smaller sub unit of the RNA is made up of 1500 nucleotides in length having a Svedberg coefficient of 16S. Along with the ribosomal proteins the smaller sub units have a sedimentation rate of about 30S, which is paired with the larger sub unit that has two molecules of RNA which has nearly 3000 nucleotides and has a sedimentation rate of about 23S and a short sequence of about 120 nucleotides and has a rate of about 5S.

The RNA molecules are accompanied by the proteins which gives rise to larger sub units of 50S.

The eukaryotic ribosomes are made up of about 60S and a 40S sub unit. It has two short rRNA molecules that are less than two hundred nucleotides in length and the two molecules of RNA are much longer.

In addition to all these eukaryotic ribosomes also have rRNA in mitochondria and the chloroplasts.

Ribosomes are also associated with the endoplasmic reticulum or it is present in a free-floating complex of the cytoplasm.

Function of Ribosomal RNA (rRNA)

One of the primary functions of the ribosomal RNA is the synthesis of protein, and in binding to the messenger RNA and the transfer RNA and in ensuring the codon sequence of the messenger RNA, and it is translated accurately into an amino acid sequence in the form of proteins.

In order to achieve this, rRNA has a complex three-dimensional structure which involves an internal loop and the helices and creates a specific site inside the ribosomes known as A, P and E sites.

The P site is especially for binding the growing polypeptide and the site A anchors an incoming transfer RNA which is charged with amino acid.

After the formation of a peptide bond, the transfer RNA binds shortly along with the E- site before it is leaving the ribosome.

In addition to this rRNA has also has specific sites to bind with the few ribosomal proteins and it also carefully analysis the exact residues that is present in both the RNA and the protein. Ribosomal RNAs can also be expressed in cells of the extant species.

The sequence of the core catalytic sites is highly conserved by making rRNA as a superficial tool for studying the taxonomy and the phylogenetics.

It has also been found the difference in the rate of evolution of residues on the surfaces which are interior to that of the rRNA and the nucleotides which are involved in the catalytic activity, which informs formation of a peptide bond which are appeared to have predated the appearance of life on earth.

Many of the antibiotics mostly targets the rRNA of the prokaryotes and in recent times it has been found that the binding sites for the antibiotics like streptomycin and tetracycline have been found. It has also been observed that the antibiotic resistance forms point mutations in the binding sites.

Ribosomal RNA (rRNA) Citations


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