Cord Blood Stem Cells Information

Why do different molecular structure have different effects?

My friend told me that if a medicine's molecular structure is different, it can kill a patient. But why? Note: I will appreciate it if you can give me a resource or link.

Public Comments

1. Every molecule has a different molecular binding property. The different ways that atoms combine to make molecules can give us life or death. Iron in our blood combines with oxygen to give us life. I don't know too much about poisons but they do a similar thing to give us death.