There are many kinds of RNA in living organisms with complex functions, which are generally divided into two categories: coding RNA (coding RNA) and non-coding RNA (ncRNA) according to whether they encode proteins. The former refers to mRNA, while the latter includes many types, such as the well-known tRNA and rRNA, snRNA involved in mRNA splicing, snoRNA involved in RNA modification, etc.
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There are many types of non-coding Rnas, which can be divided into two broad categories by length: Those greater than 200 nt (nucleotides) are called long non-coding Rnas (lncrnas), those less than 200 nt are called small non-coding Rnas (small Ncrnas), and those less than 50 nt can also be called tiny Ncrnas, such as siRNA, miRNA and piRNA.