Question

once an mrna molecule has been created, the molecule is not finished. there are some things that need to be added to the mrna in order to finalize it.

pre - mrna includes the non - coding sections of the dna molecule, known as introns. these need to be removed from the mrna so only the coding sections, known as exons, are included in the mrna molecule. to remember the difference between exons and introns, think exons are expressed

the finalized rna consists of the exons spliced together

image showing exon, intron, exon, intron, exon and mature mrna

which of these happens as rna is finalized?

• exons are taken out of the final rna strand, leaving only introns
• introns end up broken apart but are kept in the final rna strand
• exons are spliced together and kept in the finalized rna strand
• exons and introns leave the cell completely before rna is finalized

Explanation:

To solve this, we analyze the process of RNA finalization (splicing) from the provided text and diagram:

• The text states pre - mRNA has introns (non - coding) and exons (coding). Introns are removed, and exons are spliced together to form mature mRNA.
• Let's evaluate each option:
• Option 1: Exons are kept, introns are removed. So this is wrong.
• Option 2: Introns are removed, not kept. So this is wrong.
• Option 3: The diagram and text show exons are spliced (joined) and remain in the final mRNA. This matches the process.
• Option 4: Introns are removed before finalization, so they don't leave with exons. This is wrong.

Answer:

The option "Exons are spliced together and KEPT in the finalized RNA strand" (the third option in the list of choices).