A unique DNA does not make a human being. Until near full term, within 10 weeks or so, humans cannot survive outside the womb. You can stretch the survival but only at the cost of literally millions of dollars. That fetus is not a human being, it is the potential and that is all.
As for your analogy, life does not end at lack of heart beat or brain activity. It ends at the permanent cessation of cellular activity. Human life might end on your criteria, but not biological life.