The role of RNA in protein synthesis
1. mRNA: This is a messenger RNA, transfer the genetic detail duplicated from DNA in fashion of a sequence of 3-base code ‘term’, every term states a certain amino acid.
2. Ribosomal RNA (rRNA): It links with a batch of proteins to configure ribosomes. It is the complicated form, moves physically along with a mRNA molecule, facilitates the fabrication of various amino acids into protein chains. They also link tRNAs and different supplementary molecules necessary for protein synthesis. Ribosomes are made up of a large and small subunit, each of which having their unique rRNA molecule or molecules.
3. Transfer RNA (tRNA): It is pivotal in decrypting the key codons in mRNA. Every amino acid possesses their individual kind of tRNA, which attach it and transfer it to the expanding end of a polypeptide chain when the subsequent codon on mRNA needs it. The correct tRNA with its attached amino acid is selected at each step because each specific tRNA molecule contains a 3-base sequence that can pair with base of its reciprocal codon in the mRNA.
Every tRNA carry a set of 3 nucleotides known an anticodon. The anticodon of a said tRNA can attach to one or more particular mRNA codons.
The codons are predetermined for the tRNA thus, transferring the amino acid to that specific location.
Variety of tRNA are streaming within a cell, possessing their own anticodon along with complimentary amino acid and they attach to codons inside of the ribosome, where they remit amino acids for incorporation into the protein chain.
Thus, proteins are constructed from miniature units known as amino acids, which are described by 3-nucleotide mRNA sequences called codons.
The 3D Structure of tRNA
A tRNA is formed from a single strand of RNA in a similar fashion mRNA is formed.
However, the strand takes on a complex three dimensional structure since base pairs form between nucleotides in different parts of the molecule.
This creates double-stranded regions and loops, overlapping the tRNA into an L shape.
The tRNA molecule has a noticeable folded structure with 3 hairpin loops that form the structure of a 3-leafed clover.
One of these hairpin loops contains a sequence known as the anticodon, which can admit and decode an mRNA codon.
Every tRNA have their correlated amino acid attached to its end.
When a tRNA identifies and attaches to its corresponding codon in the ribosome, the tRNA shifts the suitable amino acid to the tip of the lengthening amino acid chain.
Then the tRNAs and ribosome carry on to decipher the mRNA molecule until the entire series is translated into a protein.
tRNA and its Decoding Role
The genetic information passed from DNA to protein via mRNA in which the nucleotide sequence of mRNA is converted into chain of the amino acid to form protein.
However, this deciphering procedure is carried out with the help of two kinds of adapter molecules: tRNAs and an enzymes known as aminoacyl-tRNA synthetases.
There are 2 functions which are performed by all tRNAs:
1. To get chemically connected to a specific amino acid and to base-pair with a codon in mRNA so as to put in the amino acid in the lengthening peptide chain.
Every tRNA molecule is exquisitely identified by the 20 aminoacyl-tRNA synthetases.
In a similar fashion, every enzyme molecules inimitably attaches the 20 amino acids to a specific tRNA, forming an aminoacyl-tRNA.
2. When the accurate amino acid is linked, then a tRNA identifies a codon in mRNA, thereby bringing its amino acid to the expanding polypeptide.
How Synthetases Recognize tRNAs.
After further studies on tRNA, 30 – 40 variety of tRNAs were recognized in bacterial cells while about 50 – 100 in animal and plant cells.
Therefore, the count of tRNAs in almost all cells is exceeding the number of amino acids observed in proteins.
Moreover, they differ from the number of codons in the genetic code.
Accordingly, several amino acids possess more than one tRNA to which they can link.
Furthermore, several tRNAs can attach to more than one codon. Aforementioned, the majority of amino acids are encoded by more than one codon, needing some tRNAs to identify more than one codon.
Function of tRNA Molecules
The function of 70 – 80 nucleotides long tRNA is based on their accurate 3D structures.
In solution, all tRNA molecules overlap into a same stem-loop setting that mimic a cloverleaf which when drawn in two dimensions.
The 4 stems are small double helices fixed by Watson-Crick base pairing; 3 out of 4 stems have loops containing 7 or 8 bases at their tail end, whereas the rest, unloop stem embody the free 3′ and 5′ ends of the chain.
3 nucleotides entitled the anticodon, located at the middle of one loop, can form base pairs with the 3 corresponding nucleotides forming a codon in mRNA.
As delineated earlier, determined aminoacyl-tRNA synthetases identifies the surface structure of every tRNA for a particular amino acid and covalently bind the specific amino acid to the unloop amino acid acceptor stem.
The 3′ terminal end of each tRNAs has the sequence CCA, which in most instance adjoins when synthesis and processing of the tRNA are finish.
Observed in 3 dimensions, the overlapped tRNA molecule has an L shape with the anticodon loop and acceptor stem forming the ends of the two arms.
Loading tRNA With an Amino Acid
Enzymes known as aminoacyl-tRNA synthetases have this pivotal role.
There is an individual synthetase enzyme for each amino acid, wherein an enzyme recognizes only particular amino acid with its respective tRNAs.
Whenever the amino acid and its tRNA binds its respective enzyme, the enzyme blends them together.
The above reaction has been powered by the “energy currency” molecule adenosine triphosphate (ATP).
Sometimes, an aminoacyl-tRNA synthetase miscalculate, wherein it attaches to the incorrect amino acid.
For instance, the threonine synthetase occasionally seize serine by coincidence and binds it to the threonine tRNA.
Fortunately, the threonine synthetase has a proofreading site, which dislodges the amino acid from the tRNA.
Genetic information is transmitted into mRNA in the form of a triplet code.
Every amino acid is encoded by surplus of 3 – base sequences, or codons, in mRNA.
Each codon identifies one amino acid, however, majority of amino acids are encoded by multiple codons.
All tRNAs have a same 3 – D structure that comprises an acceptor arm that binds a particular amino acid and a stem-loop with a 3- base anticodon sequence at its ends.
The anticodon can base-pair with its complimentary codon or codons in mRNA.
Since it is a nonstandard interplay, a tRNA may base-pair with more than one mRNA codon, and in contrast, a specific codon may base-pair with several tRNAs.
Each of the 20 aminoacyl-tRNA synthetases identifies a single amino acid and covalently links it to an associated tRNA, producing an aminoacyl-tRNA.
This reaction triggers the amino acid, so it can involve in peptide-bond development.
Transfer RNA (tRNA) Citations
- tRNA Modifications: Impact on Structure and Thermal Adaptation. Biomolecules . 2017 Apr 4;7(2):35.
- tRNA biology charges to the front. Genes Dev . 2010 Sep 1;24(17):1832-60.
- Transfer RNA: From pioneering crystallographic studies to contemporary tRNA biology. Arch Biochem Biophys . 2016 Jul 15;602:95-105.