# RNA Splicing --- **RNA splicing** is a part of [[mRNA|RNA processing]] that takes place in eukaryotes, where the unneeded introns are spliced away from the strand. Splicing takes place in the nucleus even as the [[transcription]] is still under way. ## Introns and Exons The portion of mRNA that actually code for a protein are called **exons**. The portion of mRNA that is not needed, or is "interupting" the rest of the segment are called **introns**. ### Alternative Splicing **Alternative splicing** is a process where by splicing out a different set of exons, one DNA sequence can be altered to produce a bunch of different mRNAs. Alternative splicing is controlled by proteins that bind to the RNA in the nucleus, and interact with the spliceosome. Over 90% of human genes can have alternative splicings. ![[alternative splicing.png]] ## The Spliceosome A **spliceosome** is a large and complex that catalyzes RNA splicing. It is made up of snRNPs, or "small nuclear ribonucleoproteins" and proteins. In humans there are 5 types of snRNPs and over 300 different proteins that make up the spliceosome, making it the largest macromolecular machine we have. ![[spliceosome.png]] ___