Non-coding RNAs

As much as 98% of the human genome does not code for proteins. This so-called “junk DNA” was thought to have no function, but recent research shows that virtually all of the cell’s DNA is copied into RNA. What does all this RNA actually do in the cell? In the past several years, various classes of noncoding RNAs (as opposed to messenger RNAs that code for proteins) have been discovered. One of the most actively researched noncoding RNAs are the microRNAs (miRNAs). These are extremely small, containing only 21–25 nucleotides, and were originally overlooked. However, researchers are increasingly realizing their importance in regulating gene expression in both the animal and plant kingdoms. MicroRNAs play critical regulatory roles in embryo d....²