What is the difference between exons and introns?

• A. Exons code for final mRNA and protein; introns are non-coding sequences removed during RNA splicing.
• B. Exons are non-coding; introns code for final mRNA.
• C. Exons are removed during splicing; introns become the mature mRNA.
• D. Exons and introns both code for proteins.

Answer: (A)

During gene expression in eukaryotes, the initial transcript contains both coding and non-coding segments. Exons are the parts that remain in the mature mRNA after splicing and provide the information that will be translated into protein. Introns are non-coding regions that are removed from the pre-mRNA during RNA splicing, so they do not appear in the final mRNA. As a result, the mature mRNA is made up of joined exons (plus any untranslated regions) and is what guides protein synthesis. Some genes use alternative splicing to combine exons in different ways, producing different proteins, but introns are removed and do not code for the final product.