ID #1732

During lecture, it was mentioned that there are many genes that encode mRNA, rRNA, and tRNA. If I understood correctly, I think you also said that rRNA is not unique to any given ribosome (it can be incorporated into any ribosome) and tRNA can donate amino acids toward any polypeptide chain. If all rRNAs are identical and all tRNAs are identical, why is it necessary to have multiple genes encoding identical rRNA and identical tRNA?

We were referring to a particular rRNA or tRNA molecule with regard to its potential to play a role in the synthesis of any type of protein. A tRNA that is charged with alanine, for example, can contribute that alanine to any ribosome translating any protein (as long as it needs alanine of course). But the tRNA that is charged with alanine has a different nucleotide sequence than a tRNA charged with lysine, and so on. That's why you need multiple tRNA genes. Likewise, the rRNA found in a small ribosomal subunit has the same nucleotide sequence as all the other rRNA's found in that organism's other small ribosomal subunits, but there are other rRNA molecules that go into making a functional ribosome, not just one. Each of them has its own particular sequence, which is why we have multiple rRNA genes.

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