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Why is there mRNA? | by really-joel | 2002-06-02 10:33:26 |
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Hmmm... | by xcheopis | 2002-06-02 12:58:01 |
| Some objections |
by Beorn |
2002-06-02 14:13:31 |
The fact that DNA is double-stranded can't be relevant here. The strands must be partially separated anyhow, so that the information can be trascripted to mRNA.
The binding site for ribosomes and the targeting sequences are only transcripts from the DNA, just as the rest of the mRNA is. The differences between DNA and RNA are very small, so a ribosome should be able to bind to DNA with little or no modification.
The fact that there are bound ribosomes is important though. Even if there were a cell with bound ribosomes but without a nucleus, bringing together a bound ribosome and a gene in its huge chromosome would be very slow. The small mRNA strands move a lot more easily. Nevertheless, I don't think this explains why mRNA exists. No procaryotes have bound ribosomes (i think), so mRNA must have existed for millions of years before ribosomes were bound to larger structures. |
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