What 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.