 The human genome contains over 3 billion base pairs of genetic information. If it were stretched out end to end, it would span approximately 6 feet. But each human cell that houses all this information is about 0.0002 inches across. Approximately 360,000 times smaller than the length of all of our genetic information laid out side by side. So how in the world are we able to fit that massive amount of information into a tiny cell? As always, nature came up with a clever solution. Instead of all that DNA being stuffed into cells as long, sinuous strands, which wouldn't leave room for much else and would be hard to untangle when the information is needed, the information is coiled up around a series of proteins into a highly organized, condensed structure called chromatin. As you'll see, it's similar to the process of turning wool into a knitted sweater, where each piece provides structure and organization to the next. Let's explore this concept a bit more. First, a small segment of the DNA double helix is wrapped around a collection of proteins called histones, which forms a structure called a nucleosome. Nucleosomes then fold on top of each other into a single chromatin fiber. From here, the chromatin fibers are further coiled and intertwined into a chromosome, which organizes our genetic information in the form of genes, units of DNA that provide instructions to make proteins. Each human cell has 23 pairs of chromosomes, or 46 total, which contain approximately 20,000 to 25,000 genes, all of which live inside the cell's nucleus. And here, all that neatly packaged information is responsible for making sure each cell and in turn, our whole body functions properly. It turns out that this packaging trick doesn't just save space inside a cell, but also makes sure DNA is able to do its job properly. Think of it like a coiled up elastic band. When it is compacted together, no individual strands are accessible, but you can pull away particular pieces of the coiled band as needed. Similarly, when DNA is tightly wound around histones, also called heterochromatin, it isn't accessible to the proteins required to read DNA, so those genes remain turned off. In response to environmental changes, however, histones are altered through a variety of molecular processes which triggers the DNA to uncoil into a more relaxed state, known as uchromatin. Uchromatin is accessible to DNA reading proteins, thus turning the necessary gene on. These dynamic changes in chromatin density, a process called chromatin remodeling, are important for the process of cell division, when cells copy all of their genetic material and then segregate and repackage it into the newly formed daughter cell. In non-dividing cells, chromatin remodeling allows for tighter control over when and where certain genes are activated, which ensures complex organisms like humans run like a well oiled machine. Beyond ensuring the right DNA is accessible at the right time, this packing structure also prevents DNA from getting tangled, which reduces DNA damage. The structure of chromatin is one of biology's many ingenious solutions to a mathematical challenge and simultaneously solves numerous cellular complexities. Number one, it ensures vast amounts of genetic information can fit into each cell. Number two, it enables complex organisms to diversify their functionality. And number three, it helps prevent DNA damage. More levels of biological intricacy, however, also means more opportunities for mistakes to happen. Researchers are finding that genetic mutations affecting chromatin structure are common in many types of diseases, especially cancer. While scientists are still trying to uncover the precise roles these mutations play in diseases, efforts to develop drugs that target chromatin machinery have shown promise in early clinical studies, revealing their potential to provide a new type of medicine for challenging health problems.