Covalent bonds place constraints on the shapes of biological molecules. As the size and complexity of a biomolecule increases, the chemical focus shifts from covalent bonds to noncovalent interactions. Noncovalent interactions dictate the stable, native conformations of large macromolecules and polymers while permitting the flexibility necessary for their biological functions. What characteristics of weak noncovalent interactions enable the assembly, stability, and functions of biomolecules? a. They are not affected by the surrounding aqueous environment. b. They are readily reversible, whereas covalent bonds require a much larger input of energy to break. c. They have a large aggregate strength when multiple interactions are present. d. They are stable, requiring a large amount of energy to break.

A significant amount of energy is involved in the formation or rotation of covalent bonds between neighboring neighbors. There is an additional type of interatomic interactions, called debut interactions, which are much less energetic and therefore can be broken or established very easily. Many of the events at the molecular level take place in the cells, among which specify the three-dimensional structure of the macromolecules or the stereospecific relationship between the enzyme and the substrate, respond to this type of interactions. Weak interactions of biological importance can be: hydrogen bonds, ionic interactions, hydrophobic interactions and Van der Waals forces.