MadSci Network: Biochemistry

Re: How do hydrogen bonds help maintain the proteins structure?

Date: Sun Nov 5 19:02:33 2000
Posted By: Daniel Lafontaine, Post-doc/Fellow, Biochemistry, University of Dundee
Area of science: Biochemistry
ID: 972994231.Bc

Dear Thash,

I think that I shall begin by talking a bit about the hydrogen bonds. I have seen some explications somewhere else but I’ll include it here so that you don’t have to look around.

First, hydrogen bonds (H-bonds) are not covalent bonds. They are about 10-20 times weaker than the covalent ones. The usual definition is that a hydrogen, covalently bonded to an electronegative atom (nitrogen or oxygen) can make a bond to another electronegative atom. As an example, you can view water as having multiple H-bonds and it is partly why it is a liquid at room temperature. If you heat water (above the boiling point), you force the water molecules to break their H-bonds. As a result, they can move more freely and it is why a gaz is observed. As you can imagine, H-bonds do not occur only in water but in all molecules having hydrogen, nitrogen and/or oxygen. Basically, we have selected almost everything on our planet !

Here comes the protein section. Proteins are built of amino acids. These ones are the “building blocks” of proteins and they come into different “flavors” (20 to be precise). I mean that each of them is different in their atomic composition and in their chemical structure. The primary structure of protein is just the sequence of their amino acids. At that level, there is no H-bond involved.

Most proteins contain one or more stretches of amino acids (polypeptides) that take on a characteristic structure in 3-D space. The most common of these are the alpha helix and the beta conformation secondary structure. However, in this case, H-bonds are quite importants. For example, the alpha helix relies on H-bonds between specific amino acids at regular intervals within the sequence. The structure is more or less like a corkscrew and was first worked out by Linus Pauling in 1948 (in his bed !). He received the Nobel Prize for Chemistry in 1954 for his work on molecular structure.

The tertiary structure refers to the three-dimensional structure of the entire polypeptide chain. We can think of that as the interaction between several secondary motifs and yes, it also includes H-bond interactions. Most of the time, the function of a protein relies on its three-dimensional structure. By changing the conditions of the environment, it is possible to alter the structure. For example, an increase in temperature would reduce the strength of H-bonds. As a result, the tertiary structure would be disrupted and by the same occasion the function of the protein. Finally, the quaternary structure of proteins is normally seen as complexes of 2 or more polypeptide chains held together by noncovalent forces such as H-bonds !

I hope that I have clearly answered your question and that you understand more the huge implication of H-bonds for living organisms.

I think that it is always better to see some ‘real’ structures when talking about biomolecules. You should have a look at:

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