Hydrogen bonding in living systems is the bonding of hydrogen to a more electronegative atom. Many organic molecules in organisms, such as proteins and nucleic acids, depend on hydrogen bonding to function correctly.
Electronegative elements including oxygen and fluorine tend to hold onto their electrons tightly. Electronegativity is a measure of how much an atom attracts electrons. When electronegative atoms form bonds with other atoms, they pull on the electrons harder. The electrons spend more time orbiting the more electronegative atom. This unequal distribution of electrons causes areas of partial negative and partial positive charges in compounds.
Hydrogen bonding causes the spiraling of the DNA molecule and the folding pattern of proteins. In proteins, hydrogen bonds allow the protein to fold into a three-dimensional structure important to its function. In DNA, the two sides of the molecule are held together by hydrogen bonds.