DNA is located in the ______ of the cell, while the protein synthesis machinery resides in the ______.

• A. DNA is located in the nucleus, and the protein synthesis machinery operates in the cytoplasm
• B. DNA is located in the cytoplasm, and the protein synthesis machinery operates in the nucleus
• C. DNA is mitochondrial, and the protein synthesis machinery operates in the nucleus
• D. DNA is in the nucleus, and ribosomes are in mitochondria

Answer: (A)

In eukaryotic cells, DNA stays in the nucleus where transcription occurs, while the machinery that makes proteins operates in the cytoplasm. After the genetic code is transcribed into mRNA in the nucleus, the mRNA travels to the cytoplasm where ribosomes read it and assemble amino acids into proteins. The cytoplasm houses the protein-synthesis machinery, including ribosomes (both free and on the rough endoplasmic reticulum) plus the tRNAs and factors needed for translation. Some exceptions exist—mitochondria contain their own DNA and ribosomes and can synthesize a small set of proteins—but the majority of protein synthesis happens in the cytoplasm, aligning with the statement that DNA is in the nucleus and the protein synthesis machinery resides in the cytoplasm.