The transcriber and the splicer

A template strand is written as a string of letters, from its 3′ end to its 5′ end. You will make the mRNA, find the coding strand, and cut the introns out of a hnRNA.

The idea. The mRNA pairs with the template, with U in the place of T. The coding strand is the same as the mRNA with T for U, but it is written 5′ to 3′, the same as the mRNA. Splicing removes the introns, which are given as pairs of positions.

Your tasks.

1. Finish transcribe. It gives the mRNA, written 5′ to 3′, for a template written 3′ to 5′.
2. Finish coding_strand. It gives the coding strand, written 5′ to 3′.
3. Finish splice. It takes a hnRNA and a list of introns as (start, end) positions, where the intron is hnrna[start:end], and it gives the RNA with the introns removed.