Related Clues:

• Like a Granny Smith apple
• The 'A' in DNA
• Biting, as criticism
• Heartburn cause
• Base antagonist?
• Beyond sarcastic
• See 43 Across
• Part of RNA
• Sulphuric or nitric
• Boric, e.g.
• Low-pH substance
• Acrimonious
• Sour-tasting substance
• Like vinaigrette
• Carbolic and sulphuric ender