The invention relates to isolated DNA or RNA molecules comprising at least ten contiguous bases having a sequence in a microRNA shown in SEQ ID NOs: 1-94 281-374 467- 481 497-522 or 549, except that up to thirty percent of the bases may be wobble bases, and up to 10% of the contiguous bases may be non-complementary. The invention further relates to modified single stranded microRNA molecules, isolated single stranded anti-microRNA molecules and isolated microRNP molecules. In another embodiment, the invention relates to a method for inhibiting microRNP activity in a cell.