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ID 16586

Problem 26: RNA was the first genetic molecule.

Description:
Explore how RNA can self-splice.
Transcript:
HI! Tetrahymena RNA self-splices and does it in a very specific series of steps. You find an RNA that self-splices in the same way. It also loops before splicing and the 5' end of the intron to the 3' end of the exon. You were able to figure out the six nucleotide sequence of the 3' end of the exon. Reading 5' to 3', what is the sequence of the base-pairing nucleotides on the intron starting at position #1? 5' TTTCGG 3' (No, this is a DNA sequence.) 5' GGCUUU 3' (No, this is the right sequence but it is in the wrong direction.) 5' GGCTTT 3' (No, this is a DNA sequence.) 5' UUUCGG 3' (That is correct.) G can hydrogen bond with C, and A can hydrogen bond with U. Reading 5' to 3' the complementary sequence is UUUCGG. You think that this base pairing is important for the self-splicing reaction. To prove this theory, you insert two Uracils into the intron and you find that self-splicing decreases dramatically. Other than deleting the 2 Us, how might you restore the self-splicing reaction to this RNA? Once disrupted, you can't restore the self-splicing reaction. (No, the self-splicing reaction can be restored.) Add complementary nucleotides to restore the base pairing. (That is correct.) Use a greater concentration of this RNA. (No, more RNA won't increase the self-splicing efficiency. Add a different kind of RNA. (No, a different kind of RNA won't help in the self-splicing reaction of your RNA.) To restore the self-splicing reaction to your mutated RNA, you can add complementary nucleotides to restore the base pairing. Which base pairs would you add? TT (No, adding these nucleotides will not restore base pairing.) UU (No, adding these nucleotides will not restore base pairing.) AA (That is correct.) GG (No, adding these nucleotides will not restore base pairing.) CC (No, adding these nucleotides will not restore base pairing.) You would add AA nucleotides. Where would you insert the nucleotides? Position #1 (No, inserting As here will not restore base pairing.) Position #2 (No, inserting As here will not restore base pairing.) Position #3 (That is correct.) Position #4 (No, inserting As here will not restore base pairing.) Inserting the two As at this position should restore base pairing and the efficiency of the self-splicing reaction. CONGRATULATIONS!!! YOU'RE SO SMART!
Keywords:
tetrahymena, hydrogen bond, nucleotide sequence, base pairing, complementary sequence
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