  A vital ingredient of DNA molecule named adenine may be produced by
successive addition of HCN during molecular cloud collapse and star formation.
We compute its abundance in a collapsing cloud as a function of the reaction
rate and show that in much of the circumstances the resulting amount may be
sufficient to contaminate planets, comets and meteorites. We introduce a
$f$-parameter which may be used to study the abundance where radiative
association takes place.
