What are the functions of each major class of short non-coding RNAs?

Noncoding RNAs are broken down into several classes.

• MicroRNAs are approximately 18-22 nucleotides and function in the regulation of gene expression by binding to target mRNAs, leading to mRNA degradation or translational repression. 
• Long noncoding RNAs are typically longer than 200 nucleotides. They have diverse roles in gene regulation, including modulation of chromatin structure, transcriptional regulation, and translation. 
• Small interfering RNAs are approximately 20-25 nucleotides. They mediate the RNA interference (RNAi) pathway to degrade specific mRNAs or inhibit their translation. 
• Circular RNAs are 100-999 nucleotides long and are covalently closed loop structures. They regulate gene expression by acting as microRNA sponges, interacting with RNA-binding proteins. 
• Transfer RNAs are approximately 70-90 nucleotides. They function to carry amino acids to the ribosome during protein synthesis (translation). 
• Small nuclear RNAs (snRNAs) are typically 100-300 nucleotides in length and primarily function in the splicing of pre-mRNA molecules.