Hydrophobic and Hydrophilic (World of Microbiology and Immunology)
Hydrophobic and hydrophilic forces are interactions that serve to keep chemical groups positioned close to one another. Such associations are vital for the structure of the components of microorganisms.
Hydrophobic ("water hating") interactions are created because of the uncharged nature of the involved chemical groups. An example of such a chemical group is CH3. All the bonds around the carbon atom are occupied. The chemical group is described as being nonpolar. Thus, a water molecule polar molecules unable to establish an association with the non-polar chemical group. This tends to create instability in the network of water molecules, and so is undesirable. The repulsive force of the surrounding water molecules acts to force hydrophobic regions into an association with like regions. The effect tends to be the formation of a hydrophobic "pocket" or "envelope" in a protein or a carbohydrate molecule or matrix.
Hydrophilic ("water loving) interactions are possible with polar chemical group. Water is polar because oxygen is far more electronegative than hydrogen and thus the electrons involved in an oxygen-hydrogen bond spend more time in proximity to the oxygen atom. Because of this unequal electron sharing, the oxygen atom takes on a partial negative charge and the hydrogen atom a partial positive charge. In addition, the bonds in a water molecule (oriented at 105° in a "bent" molecular shape) cannot cancel each other out. Other polar groups can then form ionic type bonds with water. Regions of proteins and other biological materials that are exposed to the environment are typically hydrophilic.
Hydrophobic and hydrophilic interactions can affect protein shape. Because of the polar or nonpolar nature of the constituent amino acid building blocks, as well as in carbohydrate and lipid constituents of microorganisms, molecules and sometimes whole microorganisms can assume shapes and orientations that depend on the intracellular or extracellular environment.
The tendency for hydrophobic regions of a protein of a lipid molecule to associate away from water is a main driving force in the folding of proteins into their dimensional configuration. Furthermore, the formation of biological membranes would be extremely difficult in the absence of hydrophobic and hydrophilic interactions. The biological molecules known as phospholipids have a hydrophilic "head" region and a nonpolar, hydrophobic "tail." These forces cause the phospholipid molecules to aggregate together so that the polar heads are oriented towards the water and the hydrophobic tails are buried inside. The effect is to spontaneously establish a membrane. Insertion of functionally specialized proteins into this socalled phospholipid bilayer acts to create a biological membrane of great complexity.
See also Bacterial membranes and cell wall; Biochemical analysis techniques; Biochemistry; Cell membrane transport; Membrane fluidity