 The heart of protein synthesis is the translation of nucleotide sequence information in the form of codons into amino acids. This is accomplished by tRNA molecules which act as adapters between codons and the amino acids they specify. There are many types of tRNA molecules but each is attached to a specified amino acid and each recognizes a particular codon or codons in the mRNA because most tRNA recognize more than one codon. So, every tRNA will be attached to a special type of amino acid and will identify a specific or two or three types of codons. tRNA molecules are between 75 and 95 nucleotides in length. Although the exact sequence varies, all tRNAs have certain features in common. First, all tRNAs end at the 3 prime terminus with the sequence 5 prime CCA. So, every tRNA end will have CCA sequence. Consistent with this absolute conservation, the 3 prime end of this sequence is the site that is attached to the cognate amino acid. A second striking aspect of tRNA is the presence of several unusual bases in their primary structure. These unusual features are created post-transcriptionally by enzymatic modification of normal bases in the polynucleotide chain. So, the second striking feature is that some unusual bases are found in them. And where did these unusual bases come from? Because in normal sequences, these unusual bases are not found. So, these unusual bases are post-transcriptionally modified and created in them. For example, Pseudo uridine is derived from uridine by an isomerization in which the site of attachment of the uracil base to the ribose is switched from the nitrogen at ring position 1 to the carbon at ring position 5. So, the uracil attached to the ribose in the uridine is switched from the nitrogen at ring position 1 to the carbon at ring position 5. And this becomes Pseudo uridine. Likewise, dihydro uridine is derived from uridine by enzymatic reduction of the double bond. Between the carbons at position 5 and 6. So, in this, you can see that this is uridine and in this uridine, ribose is attached to this position. And when Pseudo uridine is formed from this position, this is changed. Now, the ribose attached to this position is attached to this position. Similarly, from uridine, there is a double bond in carbon number 5 and carbon number 6. And when dihydro uridine is formed, this double bond is removed. So, in this way, these unique types of bases are found in this. Other unusual bases found in TRNA include hyposanthin, thymine and methyl goanine. These modified bases are not essential for TRNA function. But cells lacking these modified bases show reduced rates of growth. So, if their reduced rate of growth means the role of these bases is in translation. Because reduced rates of translation means reduced rates of growth. This observation suggests that the modified bases lead to improved TRNA function. For example, hyposanthin plays an important role in the process of codon recognition by certain TRNS.