Structure and Bonding:  The Hydrogen Bond

What is the typical hydrogen bond distance found in water as ice?

Hydrogen bonds are found between hydrogen and what three highly electronegative elements?

The hydrogen bond is the strongest intermolecular force and imparts some unusual properties to a number of substances such as water, proteins, and nucleotides.  Let's examine the hydrogen bond and its importance in biological molecules.

Examine the simplified protein or short chain of amino acids below.  All side chain groups have been removed.  The is the helical form or alpha helix structure.  What holds the chain of amino acids in this form? 

Right click and select options and then click on display hydrogen bonds.  Describe the location of the hydrogen bonds in the protein.  What atoms and functional groups are involved in the hydrogen bonding?  Measure the hydrogen bond distances at three difference places and determine an average distance in the protein.

average distance __________

Look at the image of DNA given below.  Right click and select options and then click on display hydrogen bonds.  Where are the hydrogen bonds in DNA?  You may want to hold the shift key down and zoom into the molecule a little bit for a better observation.

If you are having trouble seeing the items discussed above, click here to check out a great site at the University of Massachusetts.  For a colorful version of the same- click here.

Examine the base pairs found in DNA shown below.  The pairs are adenine-thymine or AT and guanine- cytosine or GC.

AT pair                                        GC pair


Measure the hydrogen bond distances in the pairs.


Why are there only two hydrogen bonds in the AT pair, while there are three in the GC pair?

How do the hydrogen bond lengths compare in water, the protein, and the DNA base pairs?

Hydrogen bonding is a critical attractive force in the alpha-helix structure of proteins and the double helical structure of DNA; however, the arrangement of hydrogen bonds is very different in the two molecules.  Describe the arrangement of hydrogen bonds in each.

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