So remember we don't always want to synthesize a given protein inside our cells because first of all protein synthesis uses up a lot of ATP molecules. And so if we have plenty of a given polypeptide in our cell we don't actually want to synthesize anymore. So at times we want to break down our messenger RNA molecule and it's the small interfering RNA that helps break down and stimulate the breakdown of the messenger RNA molecule. And finally, we also have something called telomerase RNA component. Now, remember, inside eukaryotic cells we have these enzymes known as telomerase enzymes. And what telomerase basically does is it regulates the ends of our DNA molecules.