Our bodies contain numerous cell types that look drastically different and perform various functions that allow us to eat, breathe, move, and reproduce. While all cells have the same DNA as a “blueprint”, their working set of proteins can vary drastically.
The process of making protein from DNA is known as the “central dogma”. However, it is not a linear step, but instead requires two steps: Transcription and Translation, with an intermediate molecule, RNA.
DNA → RNA → Protein
How the central dogma is carried out on a molecular level is one of the most genius and fascinating acts of problem solving in nature. Each strand of DNA has a specific sequence of four nucleotides: A (adenine), T (thymine), C (cytosine), and G (guanine). Two bases always pair up with one another and are said to be “complementary”: A pairs with T, and C pairs with G. This pairing allows a strand to be copied into a second strand. It also allows DNA to be transcribed into RNA, where each RNA strand is a copy of a specific gene.
Before DNA can be transcribed into RNA, it first needs to become available to the transcription machinery. This is difficult because DNA is a long, tightly-packed strand located within a cell’s nucleus. Think of a cord of headphones in your pocket, only a million times longer. Before DNA can be transcribed, it needs to be unwound, and this can lead to a huge mess of coils known as “supercoils” – much like what happens when you’re unwrapping headphones. Luckily, cells have a solution for this: an enzyme called topoisomerase, which cleanly cuts one strand and resolves the coils, thus making it available to the transcription machinery, and finally stitches the DNA back together after the RNA has been made.
During translation, the information carried in RNA molecules is used to create proteins. The building blocks of proteins are amino acids, and the specific sequence of nucleotides in the RNA molecule provides the code for a specific sequence of amino acids. As such, one code is literally translated into another code: a chain of nucleotides becomes a chain of amino acids called a polypeptide chain. A polypeptide chain bends and folds on itself to form the proteins that will carry out the functions of a cell and make each cell type unique.
Contributed by Leah Bury, a postdoc at the Whitehead Institute in Cambridge, and our Featured Artist for June, 2018. To meet Leah and see more of her art, click here.