Central dogma — What is the primary role of messenger RNA (mRNA) in gene expression?

Introduction:
Gene expression involves transcription of DNA into RNA and translation of RNA into protein. This question identifies the specific function of messenger RNA within that flow of information.

Given Data / Assumptions:

• DNA encodes genes.
• RNA species include mRNA, rRNA, and tRNA with distinct roles.
• Protein synthesis occurs on ribosomes using mRNA templates.

Concept / Approach:
mRNA is synthesized by RNA polymerase as a complementary RNA copy of the coding region of a gene (using the template strand). After processing (5′ cap, splicing, poly(A) tail) in eukaryotes, the mature mRNA carries the codon sequence that directs amino acid order during translation.

Step-by-Step Solution:

Verification / Alternative check:
mRNA sequencing (RNA-seq) reads out expressed gene copies, and in vitro translation using purified mRNA demonstrates that its sequence alone encodes the protein product.

Why Other Options Are Wrong:

• Carries amino acids: tRNA, not mRNA, carries amino acids as aminoacyl-tRNA.
• Ribosome component: rRNA and ribosomal proteins form the ribosome.
• Genetic material of some organisms: RNA genomes exist in some viruses, but that is not the role of cellular mRNA.
• Catalyzes peptide bond formation: peptidyl transferase activity resides in rRNA within the large subunit.

Common Pitfalls:
Confusing the roles of different RNA classes during translation; mRNA is the template, tRNA is the adaptor, and rRNA is the catalytic/structural core.

Final Answer:
It is a direct copy of a gene.