Hydrogen bonding in life

Hydrogen bonding is a subclass of permanent dipole-dipole forces. This intermolecular force is present in some of the most key molecules needed for life, such as water and DNA.

Water

As liquids go, water is a pretty strange one. Despite being a small molecule, it has an unusually high boiling point and specific heat capacity and is one of the few liquids that is denser than its own solid. All of these properties are due to hydrogen bonding. The strength of hydrogen bonds means they require a lot of energy to overcome, which explains why water has a relatively high boiling point. But hydrogen bonding does not just pull molecules more strongly together - it can also set them apart. In ice, for instance, the hydrogen bonds are strong enough to determine the crystal structure. Here, the molecules are separated more than in the liquid, and as a result, ice floats on water!

DNA (deoxyribonucleic acid)

DNA is present in almost every cell in our body and is an essential building block for life. The key role of DNA is to house bases, or cellular code, within its double helix so the code can be read by the relevant machinery when needed. However, this poses a problem. DNA bases need to be buried and protected in the double helix to prevent damage but still be accessible to be read when required. The solution? You guessed it - hydrogen bonds. Hydrogen bonds are strong enough to keep the bases close and protected within the helix but weak enough to overcome and allow access to the bases when needed.

Figure 1: Hydrogen bonding between water molecules and DNA base pairs