After a precursor mRNA molecule is transcribed from a eukaryotic gene, it is modified. What is cut out and spliced back together to produce a molecule of mRNA?

The process of modifying precursor mRNA (pre-mRNA) in eukaryotic cells is known as RNA splicing. During this process, introns and exons play crucial roles. Exons are the coding regions of the gene that will eventually be translated into protein, while introns are non-coding regions that are not translated.

After the pre-mRNA is synthesized, introns are removed through a process called splicing, and the remaining exons are then joined together to form the final messenger RNA (mRNA) molecule. This modification is essential for the production of functional proteins because only the exons contain the necessary coding information.

The option that correctly describes which elements are cut out and spliced back together in this context identifies introns as the components that are removed, while exons are the segments that are joined to create the mature mRNA. Understanding this process is vital for comprehending how gene expression is regulated and how proteins are synthesized in eukaryotic organisms.