within a molecule. Hydrogen bonding is usually stronger than normal dipole
forces between molecules, but not as strong as normal ionic or covalent
bonds.
The hydrogen bond is of fundamental importance in biology. The hydrogen bond is said to be the ‘bond of life’. The double helix structure of DNA is
formed and held together with hydrogen bonds (see Section 4.8.2). The
nature of the hydrogen bonds in proteins dictates their properties and
behaviour. Intramolecular hydrogen bonds (within the molecule) in proteins
result in the formation of globular proteins, e.g. enzymes or hormones. On
the other hand, intermolecular hydrogen bonds (between different molecules) tend to give insoluble proteins such as fibrous protein. Cellulose, a
polysaccharide, molecules are held together through hydrogen bonding,
which provides plants with rigidity and protection (see Section 6.3.10). In
drug–receptor binding, hydrogen bonding often plays an important role.
2.6 Significance of chemical bonding in drug–receptor
interactions
Most drugs interact with receptor sites localized in macromolecules that
have protein-like properties and specific three-dimensional shapes. A
receptor is the specific chemical constituents of the cell with which a
drug interacts to produce its pharmacological effects. One may consider that
every protein that acts as the molecular target for a certain drug should be
called a receptor. However, this term mainly incorporates those proteins that
play an important role in the intercellular communication via chemical
messengers. As such, enzymes, ion channels and carriers are usually not
classified as receptors. The term receptor is mostly reserved for those
protein structures that serve as intracellular antennas for chemical messengers. Upon recognition of the appropriate chemical signal (known as the
ligand), the receptor proteins transmit the signal into a biochemical change
in the target cell via a wide variety of possible pathways.
A minimum three-point attachment of a drug to a receptor site is essential
for the desired effect. In most cases, a specific chemical structure is required
for the receptor site and a complementary drug structure. Slight changes in
the molecular structure of the drug may drastically change specificity, and
thus the efficacy. However, there are some drugs that act exclusively by
physical means outside cells, and do not involve any binding to the
receptors. These sites include external surfaces of skin and gastrointestinal
tract. Drugs also act outside cell membranes by chemical interactions, e.g.
neutralization of stomach acid by antacids.
Drug þ Receptor ! DrugÀReceptor Complex ! Altered Function
2.6 SIGNIFICANCE OF CHEMICAL BONDING IN DRUG–RECEPTOR INTERACTIONS
31
forces between molecules, but not as strong as normal ionic or covalent
bonds.
The hydrogen bond is of fundamental importance in biology. The hydrogen bond is said to be the ‘bond of life’. The double helix structure of DNA is
formed and held together with hydrogen bonds (see Section 4.8.2). The
nature of the hydrogen bonds in proteins dictates their properties and
behaviour. Intramolecular hydrogen bonds (within the molecule) in proteins
result in the formation of globular proteins, e.g. enzymes or hormones. On
the other hand, intermolecular hydrogen bonds (between different molecules) tend to give insoluble proteins such as fibrous protein. Cellulose, a
polysaccharide, molecules are held together through hydrogen bonding,
which provides plants with rigidity and protection (see Section 6.3.10). In
drug–receptor binding, hydrogen bonding often plays an important role.
2.6 Significance of chemical bonding in drug–receptor
interactions
Most drugs interact with receptor sites localized in macromolecules that
have protein-like properties and specific three-dimensional shapes. A
receptor is the specific chemical constituents of the cell with which a
drug interacts to produce its pharmacological effects. One may consider that
every protein that acts as the molecular target for a certain drug should be
called a receptor. However, this term mainly incorporates those proteins that
play an important role in the intercellular communication via chemical
messengers. As such, enzymes, ion channels and carriers are usually not
classified as receptors. The term receptor is mostly reserved for those
protein structures that serve as intracellular antennas for chemical messengers. Upon recognition of the appropriate chemical signal (known as the
ligand), the receptor proteins transmit the signal into a biochemical change
in the target cell via a wide variety of possible pathways.
A minimum three-point attachment of a drug to a receptor site is essential
for the desired effect. In most cases, a specific chemical structure is required
for the receptor site and a complementary drug structure. Slight changes in
the molecular structure of the drug may drastically change specificity, and
thus the efficacy. However, there are some drugs that act exclusively by
physical means outside cells, and do not involve any binding to the
receptors. These sites include external surfaces of skin and gastrointestinal
tract. Drugs also act outside cell membranes by chemical interactions, e.g.
neutralization of stomach acid by antacids.
Drug þ Receptor ! DrugÀReceptor Complex ! Altered Function
2.6 SIGNIFICANCE OF CHEMICAL BONDING IN DRUG–RECEPTOR INTERACTIONS
31