Alternative splicing example

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The C. elegans gene egl-15 encodes a growth factor receptor protein. The gene can produce several different versions (isoforms) of this protein that have unique functions in fluid homeostasis and cellular migration during development. One variation in the mRNAs for these isoforms is two different possible splicing patterns for the fifth exon. These two alternative exons are known as 5A and 5B. EGL-15 isoform A protein utilizes Exon 5A, which is 351 nucleotides. EGL-15 isoform B protein utilizes Exon 5B, which is 195 nucleotides.

A. Assuming the remaining coding exon sequences are the same between the EGL-15A and EGL-15B isoform mRNAs, which isoform is longer and by how many amino acids?

B. An additional EGL-15 isoform (F) protein utilizes Exon 5A like isoform A, but utilizes an additional exon to produce a protein 51 amino acids longer than ELG-15A with a different C-terminal amino acid sequence. Is the additional exon upstream (5') or downstream (3') of exon 5A and what is the length of this additional exon in nucleotides?

C. Several additional forms of egl-15 mRNA have been identified that include additional 3' exons downstream of a stop codon. Do these mRNAs produce new protein isoforms? Explain why or why not.