The PAS technique targets which class of molecules in fungal cell walls?

• A. Lipids
• B. Carbohydrates
• C. Proteins
• D. Nucleic acids

Answer: (B)

Periodic acid– Schiff staining targets carbohydrates. Periodic acid oxidizes vicinal diols in sugar units to form aldehyde groups, and Schiff reagent then reacts with those aldehydes to yield a magenta color. Fungal cell walls are rich in polysaccharides like chitin and beta-glucans, which contain many sugar units with vicinal diols, so they stain vividly with PAS. Lipids, most proteins, and nucleic acids don’t provide the same aldehyde-forming chemistry under PAS conditions, so they don’t produce the characteristic positive signal in fungal cell walls.