( They ( ( are ( ( ( completely dependant ) ( upon ( ( their ( host 's ) ) ( living cells ) ) ) ) ( to ( ( produce ( new virus ) ) ( nucleic ( acid ( and ( structural proteins ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP They)) (VP (VBP are) (ADJP (ADJP (RB completely) (JJ dependant)) (PP (IN upon) (NP (NP (PRP$ their) (NN host) (POS 's)) (NN living) (NNS cells))) (S (VP (TO to) (VP (VB produce) (NP (JJ new) (NN virus)) (NP (JJ nucleic) (JJ acid) (CC and) (JJ structural) (NNS proteins))))))) (. .)))
They are completely dependant upon their host's living cells to produce new virus nucleic acid and structural proteins.
(ROOT (S (NP (JJ Nucleic) (NNS acids)) (VP (VBP are) (VP (VBN found) (PP (IN in) (S (RB all) (VP (VBG living) (NP (NNS cells) (CC and) (NNS viruses))))))) (. .)))
Nucleic acids are found in all living cells and  viruses.