In what part of the cell does replication occur?

• A. Nucleus
• B. Cytoplasm
• C. Ribosome
• D. Nucleolus

Answer: (A)

DNA replication copies the cell’s genome, and in eukaryotic cells this happens in the nucleus, where the chromosomes reside. The nuclear envelope keeps DNA contained while replication machinery—DNA polymerases, helicases, primases, ligases—unwinds the double helix at origins and synthesizes new strands, producing semi-conservative copies during S phase. The cytoplasm hosts many other cellular processes, and in organisms without a nucleus (prokaryotes) replication occurs there. The ribosome is the protein-synthesis machinery, not where DNA is copied. The nucleolus is a subregion of the nucleus where rRNA is produced and ribosome assembly begins, not the site of DNA replication.