Acetyl Salicylic Acid (exploring the structure)

Aspirin is composed of two parts: an acetyl group attached to a salicylic acid. When it attacks cyclooxygenase, it connects its acetyl group to a serine amino acid, permanently inactiving the enzyme. The acetyl group is attached to the serine amino acid ans the salicylic acid is bound close by.  

First picture is from Acetylsalicylic Acid, and second one is just Salicylic acid.