The importance of hydrogen bonds in living organisms
Hydrogen bonds are of great importance throughout living organisms. They are weak and formed between hydrogen atoms and other atoms, normally oxygen, which are nevertheless cumulatively strong.
An example of hydrogen bonds is between water molecules in the process of cohesion tension which occurs in plants during transpiration. As water evaporates from mesophyll cells in the leaf into air spaces, more water is drawn up due to cohesion. In addition, some hydrogen bonds are formed between the water and the xylem wall, aiding transfer up, which is adhesion. These are useful in that they allow more water necessary for photosynthesis to reach the leaves where it is used in photolysis to replace lost electrons in the chlorophyll. Without this form of mass transport, plants would not be able to photosynthesise and therefore they wouldn’t survive and thus it is highly important.
Hydrogen bonds are also present in the carbohydrate polymer of cellulose. Cellulose is the excess store of glucose in a plant and is formed from straight, unbranched chains of beta glucose which form hydrogen bonds between each other to make up micro-fibrils. These provide great structural strength to the molecule and so give strength to the cell walls of plants. Cellulose does not cause osmotic problems because it is a large insoluble molecule. In addition, hydrogen bonds are found in proteins. They occur in the secondary structure, causing localised features of alpha helixes and beta pleated sheets and in the tertiary structure forming the overall shape of the protein by connecting more distant sections.
This feature of proteins, to form the specificity of the active site is particularly important in enzymes. Enzymes have a specific active site determined by the tertiary structure and this is only complementary to a single substrate so only this substrate can bind and form an enzyme-substrate complex. This was earlier described as the lock and key...