Which chromatin structure is stained most intensely by hematoxylin?

• A. Heterochromatin
• B. Euchromatin
• C. Nucleolus
• D. Nuclear envelope

Answer: (A)

Hematoxylin is a basic dye that binds strongly to acidic components, mainly DNA and RNA, making basophilic structures appear blue or purple. Within the nucleus, heterochromatin is highly condensed, packing a large amount of DNA into a small area. This high DNA density provides many binding sites for hematoxylin, so heterochromatin stains the darkest and most intensely. Euchromatin, being less condensed, has fewer DNA per unit area and thus stains less intensely. The nucleolus also stains basophilic because of its RNA content, but its staining intensity can vary and it’s not typically as dark as heterochromatin. The nuclear envelope isn’t a nucleic acid-rich region, so it doesn’t take up hematoxylin as strongly. So the most intensely stained structure is heterochromatin.