Ribosomes are ribonucleoprotein particles. They are bounded to the endoplasmic reticulum by ribophorins protein. The ribosomes are the site of protein synthesis. RNA synthesis (transcription) takes place in nucleus in eukaryotes and cytoplasm of prokaryotes. RNA is synthesized in micleolus. DNA synthesis (replication) takes place during S-phase of interphase in the nucleus of eukaryotic cell.