Concept 42 -...

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Concept 18.3 Noncoding RNAs play multiple roles in controlling gene expression. Only 1.5% of the human genome codes for proteins. Of the remainder, only a very small fraction consists of genes for ribosomal RNA and transfer  RNA. Until recently, it was assumed that most of the rest of the DNA was untranscribed. Recent data  have challenged that assumption, however. In one study of two human chromosomes, it was found that ten times as much of the genome  was transcribed as was predicted by the number of protein-coding exons present. Introns accounted for only a small fraction of this transcribed, nontranslated RNA. A significant amount of the genome may be transcribed into non–protein-coding RNAs (or  noncoding RNAs) , including a variety of small RNAs. These discoveries suggest that there may be a large, diverse population of RNA molecules that  play crucial roles in regulating gene expression in the cell. MicroRNAs can bind to complementary sequences in mRNA molecules.
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Concept 42 -...

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