Alkaloids are a class of about 3000 nitrogenous compounds made in plants. They include substances, such as morphine (a narcotic) and colchicine (microtubule assembly inhibitor). Many of these substances have potent physiological effects in animals, but their function in plant metabolism is not well understood. Many alkaloids are derived from the aromatic amino acids tyrosine and phenylalanine.

1. Alkaloid Biosynthesis I

2. Alkaloid Biosynthesis II