Carbon is what makes life as we know it exist. It makes up 18 percent of the weight of the human body, and all molecules in the body (except water)—such as sugars, proteins, fats, and DNA—contain carbon. Due to its unique electron configuration, carbon needs to share electrons. It can form four covalent bonds with other carbon atoms or a variety of other elements, forming long chains of molecules, each with a different property. In addition, it forms bonds with many other molecules, from hydrogen and oxygen to even some metals.