Protein Secondary Structure Section E
LOCAL HYDROGEN BONDING FORMS SECONDARY STRUCTURE
Secondary Structure is formed by local Hydrogen Bonding between the Hydrogen on the Nitrogen of one amide in a peptide bond with carbonyl oxygen of another amide in a second peptide bond.
Hydrogen bonds (H-bonds)are weak non-covalent bonds. The energy required to break an H-bond is about 1 to 4 kcal/mole as compared to a covalent bond which requires about 100 kcal/mole to break. Thus, H-bonds are a bit flexible and for example, the H-bonds holding water together as liquid constantly break and reform. However, in more directed H-bonds like found in protein secondary structure, the pair of groups involved stay as partners and with the overall arrangement of a single H-bond being stabilized by a group of H-bonds. So H-bonding in secondary structure is stronger due to the local grouping of these bonds and secondary structure forms like the alpha-helix and beta-sheet are neighborhoods of H-bonds acting together like a group.
Figure 7. Hydrogen Bond (H-Bond) between Two Peptide Bonds.
Figure 8. Model of Right-Handed Alpha-Helix Showing H-Bonding
(From Voet/Biochemistry 1990 John Wiley)
Figure 9. Model of Beta Sheet Showing H-Bonding between Two Strands of the Sheet.
(From Voet/Biochemistry ©1990 John Wiley)
©Wilbur H. Campbell, 1995; wcampbel@mtu.edu