DNA is the information, the blueprint for the structure, development and function of our cells. It is what determines that we are of the human species. EVERYTHING is made up of "chains of molecules," so what's your point?
When we die, we are no longer considered a living organism, and therefore, a dead human is dissimilar to a fertilized egg at the point of conception because it is a living organism according to the biological definition of life. If an organism possesses both human DNA and the characteristics of life, chances are that organism is a human being with all the rights inherent. No other argument can be made that has any facts to stand on.