Which statement accurately describes mucin properties?

• A. Mucin stains with basic dyes and is metachromatic, precipitated by acetic acid (except gastric mucin), and soluble in alkaline solution
• B. Mucin stains only with acidic dyes and is insoluble in alkaline solution
• C. Mucin is never precipitated by acids
• D. Mucin cannot be stained by any routine dye

Answer: (A)

The important idea here is how mucin behaves with dyes and chemical treatments in histology. Mucin is an acidic glycoprotein rich in negatively charged groups, so it readily binds basic dyes and can show metachromasia in certain dye systems. That means tissues containing mucin can shift color in metachromatic stains beyond the color of the dye itself. When acetic acid is applied, mucin tends to precipitate out of solution, a property often used to distinguish different mucin types, with gastric mucin showing an exception to this precipitation behavior. Additionally, in alkaline solutions, mucin dissolves because the alkaline environment reduces its interactions that hold it in place with dyes and allows it to go back into solution.

This combination—staining with basic dyes and displaying metachromasia, precipitating with acetic acid (except for gastric mucin), and dissolving in alkali—best describes how mucin behaves in routine and special staining contexts. The other statements conflict with these observed properties, such as claiming mucin stains only with acidic dyes, or that it’s never precipitated by acids, or that it cannot be stained by routine dyes.