23.          RNA

Primary Structure of tRNA

The linear sequence of ribonucleotides that are linked by phospho diester bond are known as primary structure of RNA. The phospho diester bond formed between 3' OH of ribose sugar of one nucleotide and the 5' phosphate of another ribonucleotide.

Secondary Structure of tRNA

tRNA molecule mostly forms a clover leaf structure. tRNA is a 73-93 ribonucleotide chain and this chain folds into cloverleaf like secondary structure. In this structure arms loops and stem are found. A well defined stem make up an acceptor arm, a D arm and loop, Anticodon arm and loop and a single T-arm and loop. In all arms and loop numbering of ribonucleotides are usually conserved and constant. CCA sequence is present at the 3' end terminal position. In the anticodon loop three anticodon bases are out in a prominent position. This anticodon region can base pair with the complementary codon on an mRNA. This leaf like structure of tRNA allows the addition of an amino acid to the 3' end by the enzyme amino-acyl tRNA synthetase. The hydrogen bond stabilized the structure. The 2' structure of RNA is more stable than its 3' structure.

Tertiary Structure of tRNA

In the tertiary structure of tRNA poly ribonucleiotides chain folded in to three dimensional structure. Hydrogen bonds and hydrophobic interaction stabilize the 3° tRNA and producing a compactly coiled globular structure. This compact coiled globular structure look like the ‘L’ shape.

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