View source for Essay !11 - Number of genes encoding tRNA and deducting why people should have that amount of tRNA gene Code : KSI0023

<p style="text-align:center"><span style="font-size:36px">&lt;Genomics&nbsp;Essay#11&gt;</span></p>

<p style="text-align:right">&nbsp;Sangin Kim</p>

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<p><span style="color:#0000FF"><strong>(1) Number of genes encoding tRNA</strong></span></p>

<p>According to tRNAscan-SE anaylsis of complete genomes, the number of tRNAs which are decoding standard 20 amino acids are 597. the number of selenoccysteine which is the 21st proteinogenic amino acid&rsquo;s tRNAs(TCA) are 3. The number of possible suppressor tRNAs (CTA, TTA) are 4 and tRNAs with undetermined or unknown isotypes 6. So, total tRNAs are 610. Among them, there are 34 tRNAs which with introns.</p>

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<p><strong><span style="color:#0000FF">(2) Why people should have that amount of tRNA gene?</span></strong></p>

<p>According to wobble theory, rules of base pairing are relaxed at the third position. As a result, a base can pair with more than one complementary base. Also, some anticodons have &lsquo;inosine&rsquo; at 3rd position. It can pair with U, C, or A. From this theory, we can speculate that we don&rsquo;t need to have 61 different tRNA molecules(except stop codon). However, even the wobble theory, the minimal 32 anticodons are needed to recognize all of the sense-codons in mRNA(Not stop. Stop tRNA doens&rsquo;t exist). Amino acids are attached to the specific tRNA through a specific aminoacyl-tRNA synthetase or a tRNA-dependent amino acid modification. So, lots of tRNA genes are redundant. From this information, we can speculate several reasons why Homo sapiens should have that amount of tRNA genes. I can organize the reasons largely into two. First reason is wobble theory and tRNA expression. We have 20 standard amino acids, also, proteinogenic such as selenoccystein. If we have 1 to 1 tRNA with amino acid, then it will be disaster when one tRNA can&rsquo;t function. Finally, it can leads to we can&rsquo;t make that amino acid. So there exist isotypes and it&rsquo;s a kind of &lsquo;spare mechanism&rsquo;. Second, there&rsquo;re lots of translational regulation mechanisms. To regulate in the translational level, there should have suppressor tRNAs like CTA or TTA.</p>

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