After the First and Before the Second Chemical Step of RNA

Question

After the first and before the second chemical step of RNA splicing, the intron of the pre-mRNA...
A) is still covalently connected to the 3' exon and has an internal branch in the shape of a lariat.
B) is still covalently connected to the 3' exon and is linear.
C) is still covalently connected to the 5' exon and has an internal branch in the shape of a lariat.
D) is still covalently connected to the 5' exon and is linear.
E) is still covalently connected to both of its flanking exons and is linear.

Accepted Answer

Due to the first transesterification step, the branch point in the intron is covalently bound to the 5' end of the intron, and the intron is no longer continuous with the upstream (5') exon.