Size is related to the main function of miRNAs, which is to target genes and superess their expression. In general, it depends on complementarity with mRNA sequence. If you know the biogenesis of miRNAs, Dicer cleave pre-miRNAs to mature miRNAs of length 21, which is loaded into AGO which has a socket size of ~21 nt. Since they are short, they have accessibility to their targets as mature mRNA is a complex secondary structure. Which is not possible with longer RNAs. These sRNAs (miRNAs) is easily to destroy by RNAase. There are tons of advantages being short read some literature like http://www.annualreviews.org/doi/abs/10.1146/annurev-biochem-060308-103103
MicroRNA first generated from 72 nt Primary RNA then underproceses 23 nt microRNA generated ... they are introns have sequences similarity in all vertibrates. ... recently microRNA found to be expressed in diseases and cancer. .. u can read on the biogenesid of microRNA
About the second part of ur question... they migrate from tumor site to othet places so they found in biological fluid
Size is related to the main function of miRNAs, which is to target genes and superess their expression. In general, it depends on complementarity with mRNA sequence. If you know the biogenesis of miRNAs, Dicer cleave pre-miRNAs to mature miRNAs of length 21, which is loaded into AGO which has a socket size of ~21 nt. Since they are short, they have accessibility to their targets as mature mRNA is a complex secondary structure. Which is not possible with longer RNAs. These sRNAs (miRNAs) is easily to destroy by RNAase. There are tons of advantages being short read some literature like http://www.annualreviews.org/doi/abs/10.1146/annurev-biochem-060308-103103
Thank You Saad and Jha, for the concepts and reference. Well i was just amused as i read more about miRNAs. Beyond this, i was looking for a concept of evolutionary advantages of being short, whether in destroying a mRNA as well as in being incorporated into exosomes.