RNA Transcription

Perhaps the two most important processes that need to occur in order for a person's genes to make them look a certain way(have a phenotype) are transcription and translation. This first entry will focus on RNA transcription and I will discuss translation in another post.

Let's think about what happens during transcription: An organism's double-stranded DNA, found in the nucleus of its cells, is used as a template or blueprint to create a single-stranded mRNA messenger molecule. Put simply, DNA is used to make RNA. But why? What's the point? Well pretend you were an architect and it took you countless hours to construct the most perfect design for a house and you were instructed by your boss to use those plans to make twenty-five houses. Would you risk giving those plans to a builder? Remember, you only have ONE copy. Reason would tell you, NO! Why would you want to trust someone with a product that you made that took you so much time? The builder could lose it, spill coffee on it, rip it, or countless other things could happen to it. It is much safer to make copies and give a copy to the builder of each house so that the integrity of the original plan is intact, right? RIGHT! Well that is how our DNA "thinks". It does not want to travel outside the nucleus to make the proteins that give us our phenotype. Instead it wants to stay safe inside the nucleus, since it is our only copy, and make copies of itself in RNA form which then get sent out to do the dirty work of making proteins. So not only does the DNA stay safe, but the process of transcription (DNA making many RNA molecules) is so much more efficient as well! Aren't our cells smart?!

Transcription occurs inside the nucleus. It is in the nucleus that the double-stranded DNA molecule unzips at a particular point and nucleotides are left unpaired and exposed. RNA polymerase, an enzyme, picks up RNA nucleotides (A,C,U,G) floating around the nucleus and base pairs it to ONE strand of DNA with exposed nucleotides. Remember, RNA is single-stranded. The strand of DNA being used as a template depends on the specific protein that needs to be made. Once the RNA nucleotides match up with the DNA, the RNA strand slides off and makes its way out of the nucleus and into the cytoplasm. The DNA double-helix rebinds and resumes its original shape. In case you are confused, here is a picture showing you the difference between the shape of double-stranded DNA and single-stranded RNA:



If this was not helpful enough, please view this video. You may need to replay it a few times, but it is very helpful!