Why should chemicals, some of which have remarkably simple structures, have such an important effect on such a complicated and large structure as a human being? The answer lies in the way that the human body operates. If we could see inside our bodies to the molecular level, we would see a magnificent array of chemical reactions taking place, keeping the body healthy and functioning. Drugs may be mere chemicals, but they are entering a world of chemical reactions with which they interact. Therefore, there should be nothing odd in the fact that they can have an effect. The surprising thing might be that they can have such specific effects. Th is is more a result of where they act in the body—the drug targets.
As life is made up of cells, then quite clearly drugs must act on cells. The structure of a typical mammalian cell is shown in Fig. All cells in the human body contain a boundary wall called the cell membrane which encloses the contents of the cell—the cytoplasm . The cell membrane seen under the electron microscope consists of two identifiable layers, each of which is made up of an ordered row of phosphoglyceride molecules, such as phosphatidylcholine ( lecithin ). The outer layer of the membrane is made up of phosphatidylcholine, whereas the inner layer is made up of phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol. Each phosphoglyceride molecule consists of a small polar head-group and two long, hydrophobic (waterhating) chains. In the cell membrane, the two layers of phospholipids are arranged such that the hydrophobic tails point towards each other and form a fatty, hydrophobic centre, while the ionic head-groups are placed at the inner and outer surfaces of the cell membrane. Th is a stable structure because the ionic, hydrophilic head-groups interact with the aqueous media inside and outside the cell, whereas the hydrophobic tails maximize hydrophobic interactions with each other and are kept away from the aqueous environments. The overall result of this structure is to construct a fatty barrier between the cell’s interior and its surroundings. The membrane is not just made up of phospholipids, however.
There are a large variety of proteins situated in the cell membrane. Some proteins lie attached to the inner or the outer surface of the membrane. Others are embedded in the membrane with part of their structure exposed to one surface or both. The extent to which these proteins are embedded within the cell membrane structure depends on the types of amino acid present. Portions of protein that are embedded in the cell membrane have a large number of hydrophobic amino acids, whereas those portions that stick out from the surface have a large number of hydrophilic amino acids. Many surface proteins also have short chains of carbohydrates attached to them and are thus classed as glycoproteins. The se carbohydrate segments are important in cell Within the cytoplasm there are several structures, one of which is the nucleus. Th is acts as the ‘control centre’ for the cell. The nucleus contains the genetic code—the DNA—which acts as the blueprint for the construction of all the cell’s proteins. There are many other structures within a cell, such as the mitochondria, the Golgi apparatus, and the endoplasmic reticulum, but it is not the purpose of this book to look at the structure and function of these organelles. Suffice it to say that different drugs act on molecular targets at different locations in the cell.
In the Absorption & Distribution process, a drug has to move across various biological membranes like cell wall, blood-brain barrier etc. the biological membrane is made up of 2 layers of phospholipids with intermingled protein molecules. All Lipid-Soluble substances get dissolved in cell membrane & they are easily permeated into the cells.
The success of antibacterial agents owes much to the fact that they can act selectively against bacterial cells rather than animal cells. This is largely because bacterial and animal cells differ both in their structure and in their biosynthetic pathways. Let us consider some of the differences between the bacterial cell (defined as prokaryotic ) […]
The medicinal chemist attempts to design and synthesize a pharmaceutical agent that has a desired biological effect on the human body or some other living system. Such a compound could also be called a ‘drug’, but this is a word that many scientists dislike because society views the term with suspicion. With media headlines such […]
The term ‘crude drug’ generally applies to the products from plants & animal origin found in a raw form. It is referred in relation to the natural products that has not been advanced in value or improved in condition by an any process or treatment beyond that which is essential for its proper packing and prevention from deteriorating.
General anaesthesia are CNS depressant that produce anaesthesia, which extends to the entire body and are characterised by a state of unconsciousness, analgesia and Amnesia with skeleton muscle relaxation and loss of reflexes. General anaesthetic are employed for surgical operations and four stages of anaesthesia may be recognised as: Stage 1 (Analgesia): The patient is […]
The useful and toxic effects of many plants and animals products were known to man since ancient times. Infact, there has been a quest for drugs and remedies since the existence of mankind itself. In early days, there was a close relationship between religion and the treatment of disease. The knowledge of the use of […]