The correct answer is polypeptide. There is a hypothesis about this question and it states that the actual function of genes in all species is to control the synthesis of polypeptides who then affect a metabolic pathway. This hypothesis was established in 1941 by the scientists George Beadle and Edward Tatum, after studying mutations of Neurospora Crassa. The research was continued by Norman Horowitz and it is considered to be the base of molecular genetics.