Intron or Exon
Location: Outside U.S.
Date: Winter 2013-14
How ribosomes know what is intron and what is exon ? And are there specific nucleotide order that is typical for each of these?
It's been discovered with several ribosomes, the exact locations were identified by noting similarites in the sequences and ending nucleotide at the intron/exon and exon/intron junctions.
"...certain characteristics exist near the ends of these introns. (i) An exon ends in T at the exon/intron junction and an intron ends in G at the intron/exon junction in all cases. (ii) For each intron, direct repeats several nucleotides long are present 5 to approximately 30 nucleotides upstream from both the exon/intron and intron/exon junctions."
Hope this helps.
Cutting out of introns happens in the nucleus. The ribosomes are located in the cytoplasm. Only the exons remain once the mRNA leaves the nucleus.
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