Hydrogen Bonds: Weak Attractions Between DNA bases.

Whenever hydrogen is covalently bonded to oxygen or nitrogen an imbalance of electrons occurs (i.e. a polar covalent bond forms) causing the hydrogen to become partially positive and the nitrogen or oxygen to become partially negative. The dotted lines below show the positive hydrogen atoms (white) attracting to negative oxygen (red) and nitrogen (blue) atoms of other bases.

If the partially positive hydrogen from one molecule attracts to the negative part of another molecule, we call this attraction a hydrogen bond. DNA makes good use of weak hydrogen bonds, because DNA strands need to zip and unzip easily in order for your genes to work properly. Weak hydrogen bonds allow for the two strands to separate (or denature) and then come back together (or hybridize) easily.