THE FORCES THAT INTERACT WITH BIOLOGICAL MOLECULES

 

COVALENT BONDS:  Molecules are formed by sharing of electrons between atoms and for covalent bonding, basically the atoms will be of the same type for example, the oxygen molecule O2, nitrogen molecule N2 are diatomic molecules made up of two atoms each.

IONIC BONDS OR ELECTROSTATIC BONDS: Ionic bonds result from the electrostatic attraction between two ionized groups of opposite charges. They are formed by transfer of one or more electrons from the outermost orbit of an electropositive atom to the outermost orbit of an electronegative atom. This transfer results in the formation of a cation and an anion, which get consequently bound by an ionic bond.  Common examples of such compounds include NaCl, KBr and NaF.

HYDROGEN BONDS:  These are formed by sharing of a hydrogen between two electron donors. Hydrogen bonds result from electrostatic attraction between an electro-negative atom and a hydrogen atom that is bonded covalently to a second electronegative atom. Normally, a hydrogen atom forms a covalent bond with only one other atom. However, a hydrogen atom covalently bonded to a donor atom, may form an additional weak association, the hydrogen bond with an acceptor atom.

In biological systems, both donors and acceptors are usually nitrogen or oxygen atoms, especially those atoms in amino (NH2) and hydroxyl (OH) groups. With regard to protein chemistry, hydrogen releasing groups are -NH (imidazole, indole,peptide); -OH (serine, threonine) and -NH2 (arginine lysine). Hydrogen accepting groups are COO–, (aspartic, glutamic) C=O (peptide); and S–S (disulphide).  The DNA structure for example is maintained by hydrogen bonding between the purine and pyrimidine residues.

HYDROPHOBIC INTERACTIONS:  Non-polar groups have a tendency to associate with each other in an aqueous environment; this is referred to as hydrophobic interaction. These are formed by interactions between nonpolar hydrophobic side chains by eliminating water molecules. The force that causes hydrophobic molecules or nonpolar portions of molecules to aggregate together rather than to dissolve in water is called the ‘hydrophobic bond’.  This serves to hold lipophilic side chains of amino acids together. Thus, nonpolar molecules will have minimum exposure to water molecules.  To understand more clearly, look at the structure of a cell membrane listed below.

 

RELATED;

1.  THE GLYCOSIDIC BOND

2. DNA THE GENETIC MATERIAL

3. NUCLEOTIDES

4. STRUCTURE AND PHYSIOLOGY OF A CELL MEMBRANE

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