Question

1. what portion of a pre - mrna molecule may be cut out and discarded before the molecule reaches the ribosome?

both exons and introns
exon
mrna molecules are not edited
intron

Explanation:

In the process of mRNA maturation, pre - mRNA contains both exons (coding regions) and introns (non - coding regions). Introns are cut out (spliced) and discarded before the mature mRNA reaches the ribosome for translation. Exons are joined together to form the mature mRNA. mRNA molecules are edited (through processes like splicing).

Answer:

intron