What is the function of a ribosome in translation?

• A. It transcribes DNA into RNA.
• B. It attaches amino acids to tRNA.
• C. It helps assemble ribosomal subunits.
• D. It reads mRNA codons and assembles amino acids into a polypeptide.

Answer: (D)

During translation, the ribosome serves as the molecular machine that converts the information in mRNA into a protein. It reads each codon on the mRNA and brings in the matching amino acid via tRNA, then catalyzes the formation of peptide bonds to join those amino acids into a growing polypeptide chain. As it progresses, the ribosome moves along the mRNA to read subsequent codons and extend the protein.

This isn’t about transcription, which is the process of copying DNA into RNA by RNA polymerase. It also isn’t about attaching amino acids to tRNA, a job done by aminoacyl-tRNA synthetases. And it isn’t primarily about assembling ribosomal subunits, which occurs earlier in ribosome biogenesis. So the function most aligned with translation is reading mRNA codons and assembling amino acids into a polypeptide.