1) From “Baruch she’amar” until “Yishtabach”, it is forbidden to say “Baruch hu uvaruch shemo” when hearing the name of Hashem. One is, however, permitted to answer Amen to any blessing, even if one is in the middle of a verse, unless it is the middle of a phrase. (Shulchan Aruch and Mishne Berurah 51)

2) Even in the middle of the verses of praise one may say the blessing of “Asher yatzar”, answer with “modim derabanan”, recite the first verse of the shema together with the congregation, and give the correct respoonses to kaddish, kedushah and “barchu”. (ibid)