 Did you know that each cell has thousands of different types of proteins? Proteins are the building blocks of our cells and they have many different important functions, like helping cells grow and communicate with other cells. To be able to make all of these different proteins, our cells use a set of instructions stored in our genes, which are made of DNA. Knowing that our cells need to make proteins, it may surprise you to learn that the instructions are actually very hard to read. What do we mean by this? Let's say you are making brunch for your friends and one person asks you to scramble eggs, then add Swiss cheese, tomato, ham and spinach. It seems simple, but in our cells, this sentence would look like this. The words in those instructions are listed in order, but they are not continuous. There's a lot of gibberish in between, so the sentence doesn't make sense. But how do our cells unravel the confusing DNA instructions to make a protein? To do this, by first copying the DNA into another type of nucleic acid called RNA, and then cutting the gibberish regions out of the RNA. This process is known as RNA splicing. Let's understand what an RNA is, how the process of splicing takes place, and why the cells bother storing and then cutting out all of the gibberish. To start to learn about the process of splicing, let's dive down into the nucleus of the cell, which houses our DNA. DNA is first transcribed into RNA. This RNA is called a pre-mRNA because it has not yet gone through splicing. It still has the gibberish mixed in with the instructions. You'll notice that the RNA contains the information for producing a protein, which are called exons, as well as extraneous, interspersed material. These gibberish regions, which do not code for protein, are called introns. The exons are also called protein coding regions, as they contain information that instructs the synthesis of the final protein, whereas the introns are a type of non-protein coding region. The introns are removed by a large protein and RNA complex called the splicisome, here shown between the first and second exons. On either end of the intron are particular RNA sequences which the splicisome brings together. Then the splicisome cuts the basis close to exon number one, forming a loop called a laryate. Next the RNA gets cleaved close to exon number two. Finally, the splicisome joins the two exons together, releasing the intron, which eventually gets degraded. This process occurs for all the introns in a given RNA. Some genes have no introns, while others have hundreds. The final spliced product is a mature messenger RNA, or in the case of your brunch, an omelet with Swiss cheese, tomato, ham, and spinach. The mature messenger RNA is now ready to be transported out of the nucleus and into the cytoplasm, where it can be translated into protein. You'll notice that there are also non-protein coding regions at opposite ends of the mature mRNA. These are called the 5' and 3' untranslated regions, UTRs. Since these regions are not removed from the pre-mRNA during RNA splicing, they are not considered introns. Although they do not make proteins, these UTRs have important functions in the initiation of translation, which is the process of making protein from RNA, and in the stabilization of the mRNA molecule to prevent degradation. Now that we know how splicing works, let's talk about why we even have introns and exons in the first place. One amazing feature of splicing is that cells can make multiple kinds of mRNA products from one gene, by including or excluding particular exons. This is called alternative splicing. Let's go back to the brunch dish your friend requested. If all the introns are spliced out, it reads, scramble eggs then add Swiss cheese, tomato, ham, and spinach. Say another friend joins you, but she's a vegetarian. Alternative splicing would remove the exon corresponding to ham, so she could have an omelette with Swiss cheese, tomato, and spinach. A lot of variety can be introduced this way. This allows cells to create many different proteins from just a small number of RNA messages. Cells in different organs or cells that are at different stages of development can use alternative splicing to produce proteins suited for their unique functions. Overall, splicing is an extremely important process. Because of it, we can produce the many varieties of proteins that contribute to the rich complexity of life.