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| A hydrogen bond can be defined as the polar interaction between an electronegative atom ([[Nitrogen]], [[Oxygen|oxygen]] or fluorine) and a hydrogen atom which is covalently bonded to another electronegative atom that is wither on the same molecuke, or on a different molecule. The bond is strongest when all three of these atoms are arranged in a way in which they can be linked along a straight line.<ref>Alberts, B et al. (2008). Molecular Biology of the Cell. 5th ed. US: Garland Science. 1268. p57.</ref>
| | See [[Hydrogen_bonds|Hydrogen Bonds]] |
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| Hydrogen bonding is extremely prevalent throughout nature and can be found in [[Water|water]], DNA base-pair interactions, protein folding, protein structure and protein-ligand binding. | |
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| == Water ==
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| A water molecule consists of one oxygen atom attached to two hydrogen atoms. A hydrogen bond can be formed between two molecules of water due to the 'unequal distribution of electrons within a water molecule'.<ref>Alberts, B et al. (2008). Molecular Biology of the Cell. 5th ed. US: Garland Science. 1268. p55</ref> The oxygen has a strong attraction for the electrons and has a negative charge, whereas the hydrogen only has a weak attraction and therefore has a slight positive charge. When these two oppositely-charged regions come close to each other, the result is a hydrogen bond.<ref>Alberts, B et al. (2008). Molecular Biology of the Cell. 5th ed. US: Garland Science. 1268. p55</ref>
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| Although water has a low molecular mass, it has an unusually high boiling point. This property can be attributed to the large amount of hydrogen bonds that exists within water. Since these bonds are difficult to break, water’s melting and boiling points are relatively high in comparison to other liquids that are similar but lack the hydrogen bonding.
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| == DNA ==
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| In the [[Helix|DNA helix]],the bases: adenine, cytosine, thymine and guanine are each linked with their complementary base by hydrogen bonding. Adenine pairs with thymine with 2 hydrogen bonds. Guanine pairs with cytosine with 3 hydrogen bonds.<ref>J.M.Berg, J.L.Tymoczko, L.Stryer,(2007) Biochemistry, 6th edition, New York: W.H.Freeman and company p112</ref>
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| == Protein ==
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| An alpha-helix contains hydrogen bonds between the N-H of one peptide bongs and the C=O of another peptide bond which is found 4 peptide bonds away on the same chain.
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| Also the individual, antiparallel strands of the beta-pleated-sheet have hydrogen bonds which connect the peptide bonds of different strands.<ref>Alberts, B et al. (2008). Molecular Biology of the Cell. 5th ed. US: Garland Science. 1268. p137</ref>
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| === References ===
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| <references />
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