What organelle aids in synthesis of DNA in cells?

The story behind the answer

Ribosomes don’t synthesize DNA—they build proteins by translating mRNA. DNA synthesis (replication) is carried out by enzymes like DNA polymerase in the nucleus of eukaryotic cells (and in the nucleoid of bacteria). Mitochondria and chloroplasts also replicate their own small genomes with similar enzymes.

Memory tip: ribosomes = protein factories; polymerases = DNA copiers. During the S phase of the cell cycle, helicase unwinds DNA, primase lays RNA primers, DNA polymerase extends the new strand, and ligase seals the gaps. So for DNA synthesis, think nucleus and polymerases, not ribosomes.