Where does translation occur and what is involved?

• A. In the ribosome; uses mRNA codons to assemble amino acids with tRNA.
• B. In the nucleus; uses DNA codons to assemble nucleotides with tRNA.
• C. In the mitochondria; uses rRNA to assemble proteins with DNA.
• D. In the chloroplast; uses mRNA to assemble lipids with tRNA.

Answer: (D)

Translation is the process that turns a messenger RNA (mRNA) sequence into a protein. This happens at ribosomes, which serve as the site of protein synthesis. The mRNA provides codons, three-nucleotide words that specify which amino acids should be added next. Transfer RNA (tRNA) molecules bring the corresponding amino acids to the ribosome, each tRNA carrying an anticodon that pairs with the mRNA codon. As the ribosome moves along the mRNA, it links amino acids together with peptide bonds, building a polypeptide chain. In cells, most translation occurs in the cytosol, and ribosomes on the rough endoplasmic reticulum synthesize proteins destined for secretion or membranes; mitochondria and chloroplasts also have their own ribosomes and can translate some of their own RNA.

The correct description aligns with this: translation occurs in the ribosome and uses mRNA codons to assemble amino acids with tRNA. The nucleus is the location for transcription, not translation; DNA codons aren’t used directly in translation, and lipids aren’t built by translating mRNA with tRNA.