Tag: Transfer RNA (tRNA)
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Transfer RNA (tRNA): Definition, Structure, and, Function
Continue ReadingThe 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.
About tRNA
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.
tRNA Summary
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.
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Transfer RNA (tRNA): Function, Definition, and Structure
Continue ReadingWhat is Transfer RNA (tRNA)?
Transfer RNA which is abbreviated as tRNA is also referred to s-RNA or Soluble RNA in older times.
It is considered as one of the adaptor molecules and it is composed of RNA containing about 76 to 90 nucleotides along the length which serves as the physical link between mRNA and the sequence of amino acid of proteins. t-RNA carries an amino acid for the synthesis of proteins in a cell to the ribosomes.
Complementation of the 3-nucleotide codon in the mRNA by the 3-nucleotide anticodon of the tRNA and results in synthesis of the proteins depending on the mRNA code.
tRNAs are also considered as the vital component for the process of translation which is one of the biological process in producing the new proteins following the genetic code.
Role of Transfer RNA (tRNA)
When the specific nucleotide sequences of the mRNA specify the amino acids, they are incorporated into the protein product which is known as gene further from that mRNA are transcribed.
The vital role of tRNA is to specify thy the sequences from the genetic code corresponding to that of the amino acid.
The mRNA encodes a protein with a series of codon, where each is recognized by a particular tRNA.
One end of tRNA matches a genetic codon with a three-nucleotide sequence called as anticodon.
The anticodon then forms 3 complementary base pairs with a codon in the mRNA during the biosynthesis of protein.
Where as on the other end the tRNA is covalently attached to the amino acid which corresponds to that of the anticodon sequence.
Each of the type of tRNA molecules are attached to their specific type of amino acid, so that each of the organism makes many types of amino acids.
There are many molecules of tRNA which have different anticodons and carry the similar amino acids.
The covalent attachment to the tRNA at the 3’ end is being catalyzed by an enzyme known as aminoacyl tRNA synthetases.
During the synthesis of protein, tRNAs attaches with the amnio acids which are then delivered to the ribosomes with the help of proteins which are known as elongation factors and it also aid in associating it with the ribosome, and synthesis a new polypeptide and translocate the ribosomes along with the mRNA.
If the anticodons of tRNAs matches the mRNA, another tRNA also bound to the ribosome and transfers the growing polypeptide chain from the 3’end of the amino acid attaches the 3’end of the newly delivered tRNA, and this reaction is being catalyzed by the ribosome.
Large number of the individual nucleotides in the tRNA may be modified chemically by methylation or deamidation.
This unusual bases at times affects the interaction with the tRNAs with ribosomes and sometimes it also occurs in anticodon to alter base pairing characters.
Structure of Transfer RNA (tRNA)
The transfer RNA structure can be categorized into primary and it is further transformed into secondary structure which looks similar to that of the clover leaf, and the tertiary structure is similar to that of the L-shaped 3D structure which allows it to fit in a P and A sites of the ribosome.
The clover structure transforms into the 3D L-shaped structure where the coaxial structures are present according to the stacking of the helices, and it is common to the tertiary structure of RNA.
The length of the arm as well as the loop in the t-RNA vary varies according to the species. The t-RNA species comprises of the following
 5-terminal phosphate group.
 Acceptor stem: It containing 7 to 9 base pairs and it is made by the 5’ terminal nucleotide with pairs with the 3’terminal nucleotide that contains CCA 3’ terminal group which is being attached to the amino acid. Usually, 3’terminal t-RNA structures are referred to as genomic tags. Acceptor stem contains non-Watson Crick base pairs.
 CCA Tail: It is a sequence of cytosine-cytosine-Adenine which is present at the 3’end of the tRNA molecule. The amino acids are loaded with the tRNA by the enzyme aminoacyl tRNA synthetases, which forms aminoacyl-tRNA which is covalently bonded to the 3’hydroxyl group in the CCA tail. This sequence is very much important for the recognition of the tRNA by certain enzymes and it is critical during translation. Where as in prokaryotes CCA sequence is transcribed into some tRNA sequences. In most prokaryotes tRNAs and the eukaryotic tRNAs the sequence of CCA is added during the process and therefore it does not appear in the tRNA gene.
 D-Arm: It is made up of 4 to 6 base pair stem which ends in a loop and often contains dihydrouridine.
 Anticodon Arm: It is made up of five base pairs and looks like a stem and ends in a loop which contains anticodon. In tRNA, 5’to 3’ end contains anticodon. But it is present in the reverse order, therefore, 3’to 5’ directionality is needed to read the mRNA from 5’to 3’end.
 T-Arm: The T-arm in the transfer RNA is made up of about five base pairs which contains the sequence of TψC, where ψ refers to pseudo uridine which is a modified form of uridine.
 Bases in the tRNA are modified by the process of methylation, which occur in several positions throughout the tRNA. The first base of the anticodon is wobble in position and it is sometimes modified as inosine- derived from adenine; queosine which is derived from Guanine; 5-methylaminomethyl-2-thiouridine is derived from the uracil and Uridine – – oxyacetic acid which is derived from uracil or as lysidine which is derived from Cytosine.
Transfer RNA (tRNA) Citations
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