Where do replication and transcription occur in eukaryotes?

• A. Nucleus
• B. Cytoplasm
• C. Mitochondria
• D. Chloroplasts

Answer: (A)

In eukaryotic cells, replication and transcription happen primarily in the nucleus because the genome is housed as chromatin within the nuclear envelope, and the enzymes that carry out these processes—DNA polymerases for replication and RNA polymerases for transcription—are nuclear. The nucleus also provides the space for necessary RNA processing and splicing before mRNA is exported to the cytoplasm, which is essential for proper gene expression. Organelles like mitochondria (and chloroplasts in plants) do carry out replication and transcription for their own smaller genomes, but these activities are localized to those organelles and do not represent the cell’s main sites of replication and transcription. Thus, the nucleus is the main site for replication and transcription in eukaryotes.