Morpholinos are small oligomers that are roughly 25 base pairs long, and they are used to block gene expression. They are similar to DNA and RNA in structure and function, but possess a different backbone which is non-ionic.
This non-ionic backbone also means that morpholinos are less likely to interact non selectively with cellular proteins, and due to their backbone being different of that of a nucleic acid, it means that enzymes that interact with nucleotides (nucleases) do not break it down and they are not degraded by cells.
They use Watson-Crick base pairing and bind to complementary nucleic acids. The morpholinos can be used in a variety of techniques such as translation blocking, they do this by binding to complementary base pairs on RNA and so stopping protein synthesis at the blocked sites. They can also be used for splice modification whereby they can change to mRNA product by interfering with the splicing of the pre-mRNA (this usually happens by deletion of an exon). The morpholinos also prevent microRNA from reaching its mature and active form by blocking the Dorsha or Dicer cleavage sites.