In an experiment Kim discovered that if a eukaryotic gene X is transcribed in vi

Question

In an experiment Kim discovered that if a eukaryotic gene X is transcribed in vitro (in the test-tube) it produces a 13, 500 nucleotides long RNA molecule. If the same gene is transcribed in vivo (in the cell), and the gene's RNA isolated from the of the cell, Tami discovered that its RNA was only 1, 200 nucleotides long. Next, she investigates the translation of the RNA. She discovers if the RNA is transcribed and then translated in vitro a protein is expressed that is 61 amino acids long, but if X is transcribed and translated in vivo it expresses a protein that is 341 amino acids long.

Explanation / Answer

This phenomena can be best described in the light of rna splicing

Eukaryotic RNA contains extensive non coding sequences called introns which interrupts the coding sequences or exons.

Transcription is the first step of gene expression, in which the DNA is copied into mRNA often called pre-mRNA, which includes exons and introns.

Invivo the pre mRNA goes under processing called RNA splicing, where the intron are removed from the sequence to generate a continuous coding structure comprising of exons. So in vivo the length of the final mRNA or the mature mRNA is shorter than the pre mRNA, also the expression of the gene through translation is complete.

While in vitro such mechanisms are not present, so during translation of the mRNA in vitro, translation occus till it encounters an intron and then the translation stops immediately.

For this reason, in the experiment, although the gene produce a 13500 sequence long partially translate-able mRNA it could translate into a 61aminoacid polypeptide, while invivo, the gene produced a fully functional mature mRNA of 1200 sequence, but produced a polypeptide of 341 amino acid residue.

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