Water is an excellent solvent , capable of dissolving many compounds. The polar character of water means that anything with a charge can dissolve in water. NaCl is table salt, and when added to water its sodium and chloride atoms disassociate. These ions have a charge. Both the positively charged sodium ions (Na+) and negatively charged chloride ions (Cl-) can readily bond to the polar water molecules and in doing so they dissolve. Compounds that dissolve readily in water are hydrophilic . Compounds that do not interact with water are hydrophobic .
This short video provides an explanation of polar covalent bonds and hydrogen bonds:
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There is an important class of molecules that have the unique ability to be both hydrophobic and hydrophilic, a property termed amphipathic. An amphipathic molecule has one end with some charge character, and the other end lacking charge. Phospholipid macromolecules are amphipathic. We will see the importance of these molecules in the discussion of phospholipids.
In conclusion, water has many important properties that are important to life. The cells of terrestrial organisms (including ours) contain greater than 70% water, and most cells are surrounded by water. This means that a large percentage of biomolecules operate in an aqueous compartment. It should not surprise you to learn that water plays an important role in the functioning of biochemicals. In the next few sections you will learn about four classes of biomolecules and about how their unique characteristics (and synthesis) involve water.