Answer: a) the removal of introns and the splicing together of exons
Step-by-step explanation:
The processing of the primary transcript in eukaryotic cells involves a complex series of steps to produce a mature mRNA molecule that can be translated into a functional protein. One of the critical processes is called RNA splicing.
In RNA splicing, introns (non-coding regions) are removed from the primary transcript, and the exons (coding regions) are joined or spliced together. This process ensures that the genetic information necessary for protein synthesis is present in the mature mRNA molecule. Introns do not code for protein and must be removed to create a functional mRNA. Exons, on the other hand, contain the protein-coding sequences.
Option "a" correctly describes this process, as it mentions the removal of introns and the splicing together of exons, which is a fundamental step in mRNA processing. Option "b" is incorrect because it suggests the removal of exons, which is not the case. Options "c" and "d" describe other processes, such as the addition of a guanine cap and a poly-A tail (c) or the attachment of introns to ribosomal RNA (d), but these are not the primary processes involved in RNA splicing. Option "e" is incorrect because it combines processes that do not occur together during mRNA processing.