mRNA processing removes introns, not joins them

Steps:

• Primary transcript (pre-mRNA) includes exons (coding) and introns (non-coding) regions.
• Maturation modifies it via 5' capping, 3' poly-A tail addition, and splicing.
• Splicing excises introns and joins exons to form mature mRNA.
• Option B misstates splicing by claiming introns are joined.

Why B is correct:

• Eukaryotic RNA splicing definition: introns are removed, exons ligated via spliceosome machinery.

Why the others are wrong:

• A: Pre-mRNA is synthesized by RNA polymerase II and processed into mature mRNA through multiple modifications.
• C: mRNA nucleotides contain ribose sugar, characteristic of all RNA molecules.
• D: Nucleotides in mRNA form phosphodiester (covalent) bonds in the sugar-phosphate backbone, linking bases indirectly.

Final answer: B