hydrogen bond

MIT Biology Hypertextbook: Chemistry Review

The possibility of hydrogen bonds (H-bonds) is a consequence of partial charges.

1.2 Hydrogen Bonds

Hydrogen bonds are formed when a hydrogen atom is shared between two molecules.

Hydrogen bonds have polarity. A hydrogen atom covalently attached to a very electronegative atom (N, O, or P) shares its partial positive charge with a second electronegative atom (N, O, or P). One example, shown above, involves the hydrogen bonding between water molecules.

Hydrogen bonds are ~5 kcal/mol in strength. These bonds are frequently found in proteins and nucleic acids, and by reinforcing each other serve to keep the protein (or nucleic acid) structure secure. But, since the hydrogen atoms in the protein could also H-bond to the surrounding water, the relative strength of protein-protein H-bonds vs. protein-H2O bonds is smaller than 5 kcal/mol.

1.5 Hydrophobic Interactions Nonpolar molecules cannot form H-bonds with H2O, and are therefore insoluble in H2O. These molecules are known as hydrophobic (water hating), as opposed to water loving hydrophilic molecules which can form H-bonds with H2O. Hydrophobic molecules tend to aggregate together in avoidance of H2O molecules; hydrophobic interactions are clearly demonstrated when you put an oil drop on water. This attraction/repulsion is known as the hydrophobic (fear of water) force. To understand the energetics driving this interaction, visualize the H2O molecules surrounding a "dissolved" molecule attempting to form the greatest number of hydrogen bonds with each other. The best energetic solution involves forcing all of the nonpolar molecules together, thus reducing the total surface area that breaks up the H2O H-bond matrix.

DNA Structure.

are held together by hydrogen bonds between the bases.

3.4 Primary through Quartenary structure

hydrogen bonded to the NH group of the amino acid four residues away (n +4).

In this way every CO and NH group of the backbone is hydrogen bonded.

hydrogen bonds are generally the strongest attraction possible between such

where amino acid n hydrogen bonded to amino acid (n +3) in a hairpin