What is Ribosomal RiboNucleic Acid (rRNA)?
In ribosomes, the Ribosomal ribonucleic acid (rRNA) is the RNA component which is one of the composition that is integral for the production of proteins in all organisms and this rRNA comprises of more than 60% of the ribosome by weight and rest being the protein by weight.
This is very essential for the activities. It attaches to mRNA and enlists tRNA to speed up and catalyse the formation of a peptide bond between two amino acids.
Ribosomes comprises of mor than 2 main rRna’s and more than 50 being proteins. It has 2 subunits – larger and smaller one.
The LSU rRNA acts as a ribozyme, catalyzing peptide bond formation.
rRNA sequences are widely used for working out evolutionary relationships among organisms, since they are of ancient origin and are found in all known forms of life.
The morphological feature of ribosome is based on the 3-D shape of the mRNA core and proteins situated in the ribosomes helps to stable the structure by connecting to its core.
The transcription of the Ribosomal RNA occurs in the nucleus, and the part where it occurs is called as the nucleoli which are dense and round shapes where the genetic loci that codes for rRNA is present.
Nucleoli are also crucial for the biogenesis of ribosomes, by sequestration of proteins of ribosomes.
Invention of Ribosomal RNA
Researchers found rRNA accidently when they were conducting research on cell fractionation which were tracing the function of RNA virus which gives rise to the cancer.
Fractionation is a procedure where in the membrane of the cell is precisely peeled off and the organelles inside the cell are kept unimpaired.
This cytoplasm which is homogenized is centrifuged so that segregation of cell organelles occurs by weight.
Initially when it was discovered it was thought that it is nothing but a sub cell organelle, microsome which helps in the process of formation of the proteins and later the actual role and significance of it were discovered.
It was also found that the ribosomes which were situated on the Endoplasmic reticulum helped in the identification and segregation of the RNA.
Till date the ribosomes are detected using sedimentation rate as in earlier conducted experiments by the effect known as Svedberg coefficient, however the coefficients cannot be sum up since they aren’t quantified.
In ribosomes of the prokaryoted when the 50S bigger subunit and 30S subunit are united they form a complex which has 70S coefficient.
Ribosomal RNA (rRNA) and mRNA translation assembly
Classification of the rRNA
Both prokaryotic and eukaryotic ribosomes are fabricated from bigger and smaller subunit and they get unified during mRNA translation.
The smaller subunit in prokaryotes is created of RNA molecule about 1500 nucleotides long with a Svedberg coefficient of 16S, when they are clubbed with proteins of ribosomes, the lesser subunit has a sedimentation rate of 30S.
This can be clubbed with the bigger subunit which contains 2 molecules of RNA:
1) which is 3000 nucleotides (23S) long.
2) is a smaller unit of 120 nucleotides (5S).
They usually go hand in hand by proteins and are in the midst that give rise to the larger 50S subunit.
The eukaryotic ribosome is comprised 60S and a 40S subunit and consists of two short rRNA molecules less than 200 nucleotides along with 2 RNA molecules that are much long– one that has over five kilobases (28S), and other one close to two kilobases (18S).
The eukaryotic ribosome has a Svedberg coefficient of 80S.
Moreover, eukaryotic cells even have a rRNA in mitochondria and chloroplasts and ribosomes are related to ER or are seen as free floating complexes within cytoplasm.
Function of rRNA
The major activity of rRNA is in protein synthesis.
It helps to attach to mRNA and transfer RNA so that the codon sequence of the mRNA is translated precisely into amino acid sequence in proteins.
To establish and form this rRNA has a evident 3-D morphology that contains internal loops and helices which makes and forms sites within the ribosome termed as A, P and E.
1) The P site helps to attach a growing polypeptide,
2) The A site anchors an incoming tRNA present with an amino acid.
3) After peptide bond formation, the tRNA binds immediately to the E site before leaving the ribosome.
rRNA also has placed for attaching to ribosomal proteins and precise diagnosis has distinguishes the exact residues in RNA as well as the protein.
Importance of rRNA
In the cell of all living organisms, rRNA is exhibited and researchers have found that it can be used as best foundation for research of taxonomy as well as phylogenetics because the series of core catalytic locations are strongly preserved.
There is a significant dissimilarity in the speed of evolution of remnant on the outer and inner aspect of rRNA.
The nucleotides which are produced in this activity like production of peptide bond seems to have preceded the origin of life on our planet.
The evolution can be traced using rRNA sequence and can give a better judgement.
In recent studies, the attachment site for novel antibiotics like streptomycin and tetracycline targets the prokaryotic rRNA have been stipulated.
It has also been postulated that point mutation in these attachment locations often results in the resistance of antibiotics.
For example, mutation in the 16S rRNA sequence results in resistance of Euglena and E. coli to streptomycin.
Alike outcome was seen for the resistance of Streptomyces to Spectinomycin while tramsmutations in the 30S rRNA results in tetracycline resistance.
On a new perspective, it has been noticed that the precursors of rRNA also known as preribosomal RNA is involved in the creation of micro RNA often found to mediate inflammation and cardiac conditions in reaction to mechanical stress.
However, the operational activity is still not elaborated.
Role of rRNA in Translation
Initiation, elongation and termination are that steps of translation and in every process it utilizes rRNA without which translation would not proceed.
mRNAs comprise of genetic details that are coded in the DNA into the cytoplasm where the nucleotide series is scrutinized by ribosomes in stretches of three bases called codons.
The 4 nucleotides, Adenine, Uracil, Guanine and Cytosine, can be assembled to make a sum of 64 triplet codons.
Each codon relates to a single amino acid and thus codes for the protein sequence.
Ribosomal RNA is related to group of proteins that makes ribosomes and this complicated assembly, which itself travel along an mRNA, speeds the conversion of amino acids into protein chains.
They also get attached to the tRNAs and various accessory molecules which are integral in synthesizing the protein formation.
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