THE BACTERIAL CELL WALL....

The bacterial cell wall

As in other organisms, the bacterial cell wall provides structural integrity to the cell. In prokaryotes, the primary function of the cell wall is to protect the cell from internal turgor pressure caused by the much higher concentrations of proteins and other molecules inside the cell compared to its external environment. The bacterial cell wall differs from that of all other organisms by the presence of peptidoglycan (poly-N-acetylglucosamine and N-acetylmuramic acid), which is located immediately outside of the cytoplasmic membrane. Peptidoglycan is responsible for the rigidity of the bacterial cell wall and for the determination of cell shape. It is relatively porous and is not considered to be a permeability barrier for small substrates. While all bacterial cell walls (with a few exceptions e.g. intracellular parasites such as Mycoplasma) contain peptidoglycan, not all cell walls have the same overall structures. There are two main types of bacterial cell walls, Gram positive and Gram negative, which are differentiated by their Gram staining characteristics. For both Gram-positive and Gram-negative bacteria, particles of approximately 2 nm can pass through the peptidoglycan.


The Gram positive cell wall
The Gram positive cell wall is characterized by the presence of a very thick peptidoglycan layer, which is responsible for the retention of the crystal violet dyes during the Gram staining procedure. It is found exclusively in organisms belonging to the Actinobacteria (or high %G+C Gram positive organisms) and the Firmicutes (or low %G+C Gram positive organisms). Bacteria within the Deinococcus-Thermus group may also exhibit Gram positive staining behaviour but contain some cell wall structures typical of Gram negative organisms. Embedded in the Gram positive cell wall are polyalcohols called teichoic acids, some of which are lipid-linked to form lipoteichoic acids. Because lipoteichoic acids are covalently linked to lipids within the cytoplasmic membrane they are responsible for linking the peptidoglycan to the cytoplasmic membrane. Teichoic acids give the Gram positive cell wall an overall negative charge due to the presence of phosphodiester bonds between teichoic acid monomers.


The Gram negative cell wall
Unlike the Gram positive cell wall, the Gram negative cell wall contains a thin peptidoglycan layer adjacent to the cytoplasmic membrane, which is responsible for the cell wall's inability to retain the crystal violet stain upon decolourisation with ethanol during Gram staining. In addition to the peptidoglycan layer, the Gram negative cell wall also contains an additional outer membrane composed by phospholipids and lipopolysaccharides which face into the external environment. As the lipopolysaccharides are highly-charged, the Gram negative cell wall has an overall negative charge. The chemical structure of the outer membrane lipopolysaccharides is often unique to specific bacterial strains (i.e. sub-species) and is responsible for many of the antigenic properties of these strains.


The bacterial cytoplasmic membrane
The bacterial cytoplasmic membrane is composed of a phospholipid bilayer and thus has all of the general functions of a cell membrane such as acting as a permeability barrier for most molecules and serving as the location for the transport of molecules into the cell. In addition to these functions, prokaryotic membranes also function in energy conservation as the location about which a proton motive force is generated. Unlike eukaryotes, bacterial membranes (with some exceptions e.g. Mycoplasma and methanotrophs) generally do not contain sterols. However, many microbes do contain structurally related compounds called hopanoids which likely fulfill the same function. Unlike eukaryotes, bacteria can have a wide variety of fatty acids within their membranes. Along with typical saturated and unsaturated fatty acids, bacteria can contain fatty acids with additional methyl, hydroxy or even cyclic groups. The relative proportions of these fatty acids can be modulated by the bacterium to maintain the optimum fluidity of the membrane (e.g. following temperature change).

As a phospholipid bilayer, the lipid portion of the outer membrane is impermeable to charged molecules. However, channels called porins are present in the outer membrane that allow for passive transport of many ions, sugars and amino acids across the outer membrane. These molecules are therefore present in the periplasm, the region between the cytoplasmic and outer membranes. The periplasm contains the peptidoglycan layer and many proteins responsible for substrate binding or hydrolysis and reception of extracellular signals. The periplasm it is thought to exist as a gel-like state rather than a liquid due to the high concentration of proteins and peptidoglycan found within it. Because of its location between the cytoplasmic and outer membranes, signals received and substrates bound are available to be transported across the cytoplasmic membrane using transport and signalling proteins imbedded there.

PROTENIS

Proteins

Proteins are large organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid residues. The sequence of amino acids in a protein is defined by a gene and encoded in the genetic code. Although this genetic code specifies 20 "standard" amino acids plus selenocysteine and - in certain archaea - pyrrolysine, the residues in a protein are sometimes chemically altered in post-translational modification: either before the protein can function in the cell, or as part of control mechanisms. Proteins can also work together to achieve a particular function, and they often associate to form stable complexes.

Like other biological macromolecules such as polysaccharides and nucleic acids, proteins are essential parts of organisms and participate in every process within cells. Many proteins are enzymes that catalyze biochemical reactions and are vital to metabolism. Proteins also have structural or mechanical functions, such as actin and myosin in muscle and the proteins in the cytoskeleton, which form a system of scaffolding that maintains cell shape. Other proteins are important in cell signaling, immune responses, cell adhesion, and the cell cycle. Proteins are also necessary in animals' diets, since animals cannot synthesize all the amino acids they need and must obtain essential amino acids from food. Through the process of digestion, animals break down ingested protein into free amino acids that are then used in metabolism.

Three possible representations of the three-dimensional structure of the protein triose phosphate isomerase. Left: all-atom representation colored by atom type. Middle: simplified representation illustrating the backbone conformation, colored by secondary structure. Right: Solvent-accessible surface representation colored by residue type (acidic residues red, basic residues blue, polar residues green, nonpolar residues white).

Classes of proteins

Historically based on SOLUBILITY of PROTEINS...

Two classes - SIMPLE & COMPLEX

SIMPLE PROTEINS: on hydrolysis include only amino acids:

1. Albumins - soluble in water (distilled), globular, most enzymes

2. Globulins - soluble in dilute aqueous solutions; insoluble in pure distilled water

3. Prolamins - insoluble in water; soluble in 50% to 90% simple alcohols

4. Glutelins - insoluble in most solvents; soluble in dilute acids/bases

5. Protamines - not based upon solubility; small MW proteins with 80% Arginine & no Cysteine

6. Histones - unique/structural: complexed w DNA, high # basic aa's - 90% Arg, Lys.

7. Scleroproteins - insoluble in most solvents fibrous structure - architectural proteins of cartilage & connective tissue.

Collagen = high Glycine, Proline, & no Cysteine when boiled makes gelatin

Keratins = proteins of skin & hair high basic aa's (Arg, His, Lys), but Cys.

Complex Proteins: on hydrolysis yield amino acids + other molecules

lipoproteins - (+ lipids) blood, membrane, & transport proteins

glycoproteins - (+ carbohydrates) antibodies, cell surface proteins

nucleoproteins - (+ nucleic acids) ribosomes & organelles

Common terminology:

dipeptide = 2 amino acids

tripeptide = 3 amino acids

peptide = short chain of amino acids (20-30)

polypeptide = many amino acids (up to 4,000)

protein = polypeptide with well defined 3D structure

ANTIBIOTICS

Antibiotics

Antibiotics are chemical substances produced by a microorganism that has the capability, in low concentration, to inhibit selectively or even to destroy bacteria and other microorganisms through an antimetabolic mechanism.

An antibiotic (from Latin anti, "against" and Greek biotikos, "fit for life") is a chemotherapeutic agent that inhibits or abolishes the growth of micro-organisms, such as bacteria, fungi, or protozoa. The term originally referred to any agent with biological activity against living organisms; however, "antibiotic" now refers to substances with anti-bacterial, anti-fungal, or anti-parasitical activity. The first widely used antibiotic compounds used in modern medicine were produced and isolated from living organisms, such as the penicillin class produced by fungi in the genus Penicillium, or streptomycin from bacteria of the genus Streptomyces. With advances in organic chemistry many antibiotics are now also obtained by chemical synthesis, such as the sulfa drugs. Many antibiotics are relatively small molecules with a molecular weight less than 2000 Da.

Testing the susceptibility of Staphylococcus aureus to antibiotics by the Kirby-Bauer disk diffusion method. Antibiotics diffuse out from antibiotic-containing disks and inhibit growth of S. aureus resulting in a zone of inhibition.


Classification

Antibiotics can be classified on the basis of the biosynthetic origin of the antiobiotic molecule.

1) Antibiotics derived form amino acid metabolism.
Example- Penicillin, Amoxicillin, Cephalosporin, Chlorampheniclol, Dactomycin etc.
2) Antibiotics derived from acetate metabolism.
Example- Tetracyclines, 2- macrolides, griseofulvin etc.
3) Antibiotics derived from carbohydrate metabolism.
Example- Amkacin, gentamicin, kanamycin etc.

HORMONES

Hormone
Hormone is chemical substance produced in the body that controls and regulates the activity of certain cells or organs.

Many hormones are secreted by specialized glands such as the thyroid gland. Hormones are essential for every activity of daily living, including the processes of digestion, metabolism, growth, reproduction, and mood control. Many hormones, such as the neurotransmitters, are active in more than one physical process.

Examples of hormones include aldosterone, antidiuretic hormone(ADH), cortisol, erythropoietin, estrogen, human chorionic gonadotropin (hCG), parathormone, progesterone, and testosterone. Epinephrine (adrenaline), a catecholamine-type hormone

Chemical classes of hormones.
Vertebrate hormones fall into three chemical classes:

(1)Amine-derived hormones are derivatives of the amino acids tyrosine and tryptophan. Examples are catecholamines and thyroxine.

(2)Peptide hormones consist of chains of amino acids. Examples of small peptide hormones are TRH and vasopressin. Peptides composed of scores or hundreds of amino acids are referred to as proteins. Examples of protein hormones include insulin and growth hormone. More complex protein hormones bear carbohydrate side chains and are called glycoprotein hormones. Luteinizing hormone, follicle-stimulating hormone and thyroid-stimulating hormone are glycoprotein hormones.

(3)Lipid and phospholipid-derived hormones derive from lipids such as linoleic acid and arachidonic acid and phospholipids. The main classes are the steroid hormones that derive from cholesterol and the eicosanoids. Examples of steroid hormones are testosterone and cortisol. Sterol hormones such as calcitriol are a homologous system. The adrenal cortex and the gonads are primary sources of steroid hormones. Examples of eicosanoids are the widely studied prostaglandins.

RESINS

Resin

Resin, not to be confused with rosin, is a hydrocarbon secretion of many plants, particularly coniferous trees. It is valued for its chemical constituents and uses, such as varnishes and adhesives, as an important source of raw materials for organic synthesis, or for incense and perfume. Fossilized resins are the source of amber. All resins are practically insoluble in water. They dissolve more or less completely ill organic solvents, e.g. alcohol, oil of turpentine; those containing resin acids are usually proportionately soluble in alkalis. A solution of a resin in a volatile solvent, when painted on a smooth surface should rapidly and completely dry to form a hard transparent film; to be suitable for varnish the film should not darken with age or become impaired upon exposure to light or moisture.

Classification-
Various more or less unsatisfactory attempts have been made to classify resins according to principal components; the following classification is as follows.

1.Resins consisting principally of Resin and other Esters. Together with free Aromatic Acids.Resin, Resin or other Gum-Resin Esters Aromatic Acids or Oleo-Resin.

Benzoin (sumatra) {Benzoresinol and Sumaresinotannol}Cinnamic Acid 11 % combined with cinnamic and benzoic acids 60% Benzoic Acid 9%.

Asafetida. Asaresinotannol combined with ferulic acid.

Balsam of Peru. Peruresinotannol combined with cinnamic and benzoic acids 28%. Benzyl benzoate and cinnamate 58 - 70%.

Storax. Storesinol, free and combined with 35-40% Cinnamic Acid 16-24% Storax Cinnamates of ethyl phenylpropyl and 25% cinnamyl alcohols (average).

Balsam of Tolu.Toluresinotannol combined with cininamic and benzoic acids 80% Cinnamic Acid 12%.
Benzyl benzoate and cinnamate 7.5% Benzoic Acid 8%.

2. Resins consisting principally of Resin Acids. Resin, Oleo-Resin or Gum-Resin and Resin Acids : Colophony: Copaiba, Myrrh.

3. Glyco-Resins. This important and complex group comprises the glycosidal resins, which are so-called because when they are boiled with mineral acids hydrolysis takes place, with production of a sugar (usually dextrose) and a complex resin acid and simpler acids. Jalap resin and Ipomoea resin are examples of glyco-resins.

ENZYMES

Enzyme

Enzymes are biomolecules that catalyze (i.e. increase the rates of) chemical reactions. Almost all enzymes are proteins. In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into different molecules, the products. Almost all processes in a biological cell need enzymes in order to occur at significant rates. Since enzymes are extremely selective for their substrates and speed up only a few reactions from among many possibilities, the set of enzymes made in a cell determines which metabolic pathways occur in that cell.

Like all catalysts, enzymes work by lowering the activation energy for a reaction, thus dramatically increasing the rate of the reaction. Most enzyme reaction rates are millions of times faster than those of comparable uncatalyzed reactions. As with all catalysts, enzymes are not consumed by the reactions they catalyze, nor do they alter the equilibrium of these reactions. However, enzymes do differ from most other catalysts by being much more specific. Enzymes are known to catalyze about 4,000 biochemical reactions. A few RNA molecules called ribozymes catalyze reactions, with an important example being some parts of the ribosome. Synthetic molecules called artificial enzymes also display enzyme-like catalysis.

Enzyme activity can be affected by other molecules. Inhibitors are molecules that decrease enzyme activity; activators are molecules that increase activity. Many drugs and poisons are enzyme inhibitors. Activity is also affected by temperature, chemical environment (e.g. pH), and the concentration of substrate. Some enzymes are used commercially, for example, in the synthesis of antibiotics. In addition, some household products use enzymes to speed up biochemical reactions (e.g., enzymes in biological washing powders break down protein or fat stains on clothes; enzymes in meat tenderizers break down proteins, making the meat easier to chew.

Human glyoxalase I. Two zinc ions that are needed for the enzyme to catalyze its reaction are shown as purple spheres, and an enzyme inhibitor called S-hexylglutathione is shown as a space-filling model, filling the two active sites.

Enzyme Classification
We will use the comprehensive classification from the Commission on Enzymes of the International Union of Biochemistry, which classifies enzymes into six main groups. All reactions involving degradation or synthesis are catalyzed by one of these six types. Theoretically, all enzyme reactions are reversible, but conditions do not always exist to drive the reaction in reverse.

a. Oxidoreductases
These enzymes carry out the specific energy-releasing reactions for the cell. This is most often accomplished through enzymes called dehydrogenases, which, by removing hydrogen, also remove electrons. As these electrons are passed to an electron (or hydrogen) acceptor, energy is released that the cell is able to trap and store as chemical energy. Oxidation is the only major chemical source of energy for a cell, and biological oxidation is most frequently accomplished by the removal of hydrogen. It involves a loss of electrons from highly electronegative atoms and a gain of electrons by atoms of lesser electronegativity. As electrons move from one molecule to another on this trip, one reactant is oxidized while the other is reduced. Oxidation and reduction are described, therefore, as coupled reactions. Over 200 different oxidoreductases have been described.

b. Transferases
During degradation and synthesis of compounds in cells, functional chemical groups are frequently transferred from one substrate to another. This does not cause the liberation of energy from the substrate but instead converts a substrate to a compound that may then be oxidized or used for the synthesis of cellular materials. A number of special names are used to indicate reaction types (e.g. kinase) to indicate a phosphate transfer from ATP or other phosphate donor, to the named substrate.

c. Hydrolyses
These enzymes break large molecules into smaller ones. In bacteria and some fungi these enzymes are excreted by the cell into its external environment (and are called exoenzymes). In this way large insoluble compounds can be broken down in the presence of water into soluble molecules that can enter the bacterial or fungal cell and serve as nutrients. General examples of hydrolytic enzymes include:

< Cellulases - hydrolyze cellulose to glucose
< Amylases - hydrolyze starch to maltose
< Proteases - hydrolyze proteins to amino acids
< Lipases - hydrolyze fats to glycerol and fatty acids
< Nucleases - hydrolyze ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) into smaller soluble molecules. Many of the exoenzymes or hydrolases of bacteria are really digestive juices. Similar exoenzymes in human are the digestive juices that break food down into substances that are usable by the body. Some exoenzymes of bacteria are potent toxins and contribute to the disease-producing potential of bacteria by catalyzing reactions that are harmful to the host.

d. Lyases
These enzymes either (1) remove groups from substrates nonhydrolytically, usually leaving double bonds (2) add groups to both atoms involved in a double bond thus converting the double bond to a single bond.

e. Isomerases
The isomerases catalyze reactions where reactants and products do not differ in their chemical composition, but in the way chemical groups are arranged on the molecule. This is easiest to see in the case of epimerases or racemases which simply catalyze a rearrangement of the groups attached to an asymmetric carbon atom. There are epimerases, for example, that interconvert sugars by changing the positions of specific hydroxyl groups, and there are racemases the interconvert the L and D isomers of amino acids such as glutamic acid, alanine, and lysine. Mutases transfer a group such as a phosphate from one place in a molecule to another.

f. Ligases
Ligases catalyze reactions in which two molecules are linked together with the consumption of energy from ATP. These are synthesis reactions and the enzymes have been known for years as synthetases. Ligases take part in many of the steps involved in the synthesis of macromolecules such as proteins and many other compounds used as intermediates in nucleic acid biosynthesis.

It should be stressed that the action of cellular enzymes is neither sporadic or disorganized. All cells, including bacteria, have enzyme systems in which the enzymes work in an orderly sequence until a particular series of reactions has been completed. Many enzyme systems act in a kind of chain reaction; the product of one reaction become the substrate for the next reaction in the series and so on

VITAMINS

Vitamin

Vitamins are organic substances that constitute a range of many different types of organic molecule which are essential to the proper functioning of the human organism. They are formerly known as ‘accessory food factors.

For example- vitamin A, vitamin B2 etc.
A vitamin is an organic compound required as a nutrient in tiny amounts by an organism. A compound is called a vitamin when it cannot be synthesized in sufficient quantities by an organism, and must be obtained from the diet. Thus, the term is conditional both on the circumstances and the particular organism. Ascorbic acid functions as vitamin C for some animals but not others, and vitamins D and K are required in the human diet only in certain circumstances.

Vitamins have diverse biochemical functions, including function as hormones (e.g. vitamin D), antioxidants (e.g. vitamin E), and mediators of cell signaling and regulators of cell and tissue growth and differentiation (e.g. vitamin A). The largest number of vitamins (e.g. B complex vitamins) function as precursors for enzyme cofactor bio-molecules (coenzymes), that help act as catalysts and substrates in metabolism. When acting as part of a catalyst, vitamins are bound to enzymes and are called prosthetic groups. For example, biotin is part of enzymes involved in making fatty acids. Vitamins also act as coenzymes to carry chemical groups between enzymes. For example, folic acid carries various forms of carbon group – methyl, formyl and methylene - in the cell. Although these roles in assisting enzyme reactions are vitamins' best-known function, the other vitamin functions are equally important.

Classification:
According to the solubility they can be classified in two brought types –
1) Fat Soluble Vitamins
2) Water Soluble Vitamins

Fat soluble vitamins are further of four types-
a) Vitamin A (A1, A2). Example- Retinol
b) Vitamin D (D2-D6). Example- Cholecaloferol
c) Vitamin E. Example- α-Tocopherol
d) Vitamin K (K1, K2). Example- Phytonadione

Water soluble vitamins are dominated by the vitamin B complex. It also included vitamin C, biotin-
a) Vitamin B (B1-B3,B5, B6, B9, B12). Example- Thiamine, Riboflavine, Miacin etc.
b) Vitamin C. Example- Ascorbic acid
c) Vitamin H. Example- Biotin

SCOPE OF PHARMACY PROFESSION

Scope of Pharmacy Profession
•Pharmacists are one of the most accessible health professionals and work closely with patients to assist them with managing their medicines and disease states as well as promoting health and improving the quality of life.

•The role of the pharmacist encompasses counseling patients on the best use of medications, providing advice on symptoms, the management of common ailments, preparing and formulating medications and providing health education.

•Pharmacists are "experts on medicines" and play an active role in the Quality Use of Medicines in our society. Pharmacists have skills in chemistry of the drugs, formulating medicines and the therapeutic use of drugs to treat diseases.

•Pharmacists are dynamic, patient-oriented professionals committed to fulfilling the health care needs of their patients. Pharmacy is a profession that is expanding in new directions to meet the health care needs of all Canadians.

•Currently, there is a movement beyond the traditional compounding and dispensing of medication towards a more professional advisory and primary health care role. Pharmacists can apply their knowledge and skill to become directly involved in the healing and education of patients. The phrase "ask your pharmacist" is becoming increasingly common - and with good reason. Pharmacists are an integral part of the community and serve as an important source of knowledge.


Pharmacists are ready and willing to share their knowledge concerning:
•optimal drug therapy for patients with a focus on drug interactions and potential side effects.

•treatment of various medical conditions.

•education and promotion of the general health of the public.

•where to get emergency care.

Although the pharmacist’s focus is changing, the pharmacist remains an expert in the application and usage of pharmaceuticals. This includes the formulation, compounding, storage, and dispensing of medication.


Pharmacist in General Practice.
Pharmacist interested in people and in the life can take the opportunity of daily and all day contact with public, in an area where he is recognized as a family adviser, consulted upon a variety of subjects, in addition to the supply of medicines whether on prescription or required for sample family ailments. The general practice of pharmacy is an activity involving the application of profession, scientific and technological principles to the supply of medicines and medical surgical appliances required for prevention and treatment of disease under domiciliary conditions whether on prescription or otherwise and the giving of information and advice to such supply. The pharmacy is a real information centre for all who desires the service of the proprietor of the qualified staff in relation to health matters. The professional aspect of the pharmacists work can be enhanced and co-operation with the doctors practicing in his area enlarged. If the pharmacist maintains up to date record of all new medical preparations and puts this at the disposal of the local doctors.


Pharmacist in the Hospital.
A hospital pharmacy with a qualified pharmacist in charge has been accepted as a basic need by the larger hospital to explore the medical services scientifically and meaningfully. Pharmacist in a hospital works wholly in a professional manner. The practice of pharmacy in private and government owned hospitals is emerging as one of the most important areas of pharmacy practice. Broadly hospital pharmacy (i.e. pharmacy within hospital) is the department or service in a hospital which is under the direction of a professionally competent and legally qualified pharmacist from which all medications are supplied to the nursing units and other services, where special prescriptions are filled for patients in the hospital, where prescription are filled for ambulatory patients and out patients, where pharmaceuticals are manufactured in bulk, where narcotic and other prescribed drugs are dispensed where biological are stored and dispensed and where professional supplies are open stocked and dispensed.

The hospital pharmacist also acts as a pharmacologic advisor to the physician concerning the pharmacology, toxicology, and penology of new classes of drugs. Additionally the pharmacist plays a vital role in hospital management, a recent concept that is rapidly achieving recognition in the field of hospital. Current trends and progressive hospital make the need for pharmacist for every hospital because of their involvement in assuring better and safer use of drugs.


Pharmacist in Industry.
The pharmacists’ multidisciplinary background, business training and sense of accuracy control make him a uniquely qualified to serve in the pharmaceutical industry. Pharmaceutically the persons can serve in various industry capacities:

•Pharmaceutical Production
•Research and Development
•Analytical Research & Quality Control & Assurance
•Scientific Information and Regulatory Affairs
•Clinical Testing
•Professional Relations
•Sales and Marketing and Management


Pharmacist in Marketing.
Pharmaceutical marketing is not just about selling drugs. It is also about promoting new ideas. Marketing can further the idea that pharmacists provide value and should receive compensation for professional services. It can help pharmacists exert influence over the way pharmacy is practiced.

Marketing can be used to solve almost any problem in pharmacy. It can be used in personal career management, in influencing change in practice settings, and in enhancing job effectiveness. Marketing can help persuade patients to adhere to medication plans, physicians to prescribe medicines appropriately, and management to support pharmacy practice initiatives. It can be used to recruit good employees, attract and keep patients, provide innovative services, and compete with other professions for a portion of the health care pie.


Pharmacist in Government Sectors.
The emphasis on health services for the population of our country has increased the importance of participation of pharmacists in health programs. Pharmacists have a unique and broad based education to have a wide range of opportunities for careers in the clinical practice of pharmacy in governmental hospitals, out patients clinics, extended care facilities administration and health related affairs. In the united sates of America and many other developed countries, pharmacists are serving in civilian and military sectors.

(1)Opportunities in the civilian, government sectors:
Department of Health, Education and welfare (HEW)
The public Health Services (PHS)

>>The Alcohol, Drug Abuse and mental Health Administration (ADMHA):
>National Centre for family planning service
>National centre for health services, research and development
>Centre for disease control
>Maternal and child health service
>National institute of occupational safety and health
>Community health services
>>The centre for disease control (CDC)

>>The food and drugs Administration.

>>The National Institute of Health (NIH)

>>The Health Service Administration (HAS)

>>Social Rehabilitation Service (SRS)
>Veterans Administration
>The department of Justice in Drug Enforcement Administration
>Social Security Administration
>Office of Equal Opportunity
>Non Federal Government Agencies, e.g. States, Municipal Corporation etc.

(2)Opportunity in non-civilian governmental sectors:
In addition to the role of pharmacists in the governmental health agencies for the benefit of common people they also have an important responsibility regarding health affairs in Armed, Naval and Air force. Both commissioned as well as non commissioned pharmacists are found to serve in the United States.


Pharmacist in Community Health Services.
A community pharmacist is the professional who would be in direct access to the public and whose duties are widely sought after by the public and patients. He dispenses medicines with a prescription and in certain cases without a prescription where applicable (OTC drugs). As he is the person who will be in direct contact with the public, he has to play an important role in decreasing the mortality and morbidity in the public.

Community pharmacy practice evolved in the post Second World War period. A pharmacist not only began to perform functions that were new to pharmacy, but they began to innovative functions and make original contribution to literature. The popular motto of "patient oriented practice" and "drug use control" came into practice. But unfortunately the role of community pharmacist is not so much recognized till today especially in India and needs strong efforts.

Although community pharmacist is of key importance in providing better healthcare, it is the matter of shame for us that the Bangladeshi patient does not find any difference between the grocer and the pharmacist. Despite of major role of community pharmacy, the situation and condition of the community pharmaceutical service has stood where it was like a man walking on a treadmill. He walks and walks and sweats, but remains in the same place. Until and unless the link between the people and physician i.e. the pharmacist does not get its proper recognition any dreams of making us, a healthier nation cannot be fulfilled.

The need of the hour is to make community pharmacist a key towards better health care. The community pharmacist can take part in health promotion campaigns, locally and nationally, on a wide range of drug related and health related topics.

A community pharmacist involvement could play an important role in the following areas of health care.
>Nutrition Counseling
>Women Welfare-Pregnancy and Infant Care
>Rational Use of Drugs
>Sexually Transmitted Diseases-AIDS
>Alcohols, Drug Abuse and Smoking Cessation
>Family Planning
>Individualization of Drug Therapy

Community Pharmacist should have the opportunity to perform:
•General prescription services
>Dispensing of official preparation
>Manufacturers specialties
>Therapeutic information
>Clinical information as a consultant of drugs
•Clinical laboratory works e.g. preparation of some test solution like Benedict’s solution, simple pathological tests etc.


Pharmacists in the National Health Care Services.
According to the first national health insurance Act 1911 (which is revised in 1941) of Britain, the dispensing of medicines and the supply of appliances was recognized to the province of the pharmacist though medical practitioners could in many instances did supply them. The dependence on the pharmacist for dispensing of drugs and allied products is easily understood from the above act. So the pharmacist should take part in every sector of health services and must be capable to perform his duties ethically and morally.


The Pharmacist must give Reasonably Prompt Services.
He must accept a telephoned request to dispense a prescription from a medical practitioner personally known to him who undertakes to provide him with a written prescription within twenty four hours. The dispensing of prescription must be done by or under direct supervision of a qualified pharmacist. In addition to this the pharmacist should take care of his patients relating drugs and any other information regarding the drugs dispensed. Pharmacist can also take part in other activities of the health and allied services to promote and implement the government health policy.


Pharmacist in Education Sectors.
In our country numbers of Universities are offered pharmacy education program and few diploma and registered technical pharmacy courses are running. In those Institutions and Universities pharmacist plays vital roles as a teacher for the educations of the apprentices.


Conclusion.
We need to work closely with the pharmacist associations and share our common experiences and frame appropriate guidelines so that pharmacist who plays a major role in providing better health care can be recognized.

In a nutshell, pharmacist in the health care system is like circumventer of a triangle with physicians, patients and nurses at the corners of the triangle. He has direct contact with all health care professionals and patients. It is really important to appreciate the fact that a patient finds himself to be much more comfortable in a drug store than in a physician’s dispensary. The role of pharmacist is indispensable in providing better health care. Steps should be taken by the government and the pharmacist himself to make his recognition in the community as a better health care provider. The National pharmaceutical associations like Bangladesh pharmaceutical society (BPS) will have to be committed to change and use their influence to convince community and the government that pharmacists can play a significant role in national health care programs. The main driving force will have to come from pharmacists themselves. They are best able to decide what can be achieved and within what time scale.

Every community pharmacist should always remember, the following lines:
"Do all the good you can, In all the ways you can;
In all the places you can, At all the times you can;
To all the people you can, As long as ever you can".

ACUPUNCTURE

Acupuncture

What is it?
In Latin 'Acus' means needle and 'Punctura' means penetration or prick.

Acupuncture is an ancient Chinese art of Healing. Acupuncture also known as needling is the insertion of fine steel, silver or gold needles into selected areas of the skin as a remedy for disease.

There are more than 1,000 Acupuncture points in the human body located along 12 main pathways or channels in each half of the body and two channels in the mid-line of the body.
To treat a given case, an acupuncturist has to select about 8-12 points out of these 1,000.


Origin?
It was through pain and suffering of war that Acupuncture was discovered.

Some believe that Acupuncture originated in the Indus Valley civilization and then spread to Central Asia, Egypt, China and other countries of the orient.

Others believe that it spread to the oriental countries from India through Buddhist monks.
The Chinese claim it to be their own science originated about 5,000 years ago. Chinese have nursed it and brought it to its present level of popularity and scientific acceptance.

The 'Huang Di Nei Jing' is the foundation stone of traditional Chinese medicine.

It is said to be the oldest medical text in the world. A special section of it, called Ling Shu is devoted to Acupuncture and moxibustion ( a method of Acupuncture without needles).

The Chinese traditionally consider it more as a preventive science than a curative science.


Principles Acupuncture.
According to Chinese philosophy, the human body is governed by 'Chi' which is continuously circulating along the acupuncture channels.

CHI or life energy is one of the most fundamental concepts of Chinese thinking.

It is described as a basis of every living and non living entity of 'Brahmand' (cosmos), its nearest equivalent in Hindu Philosophy is PRANA.


YIN & YANG ?
The CHI consists of two dynamically opposite yet harmonising energies called YIN and YANG.

YIN signifies the female and negative energy, while YANG signifies the male and positive energy.

In health, YIN and YANG are in perfect balance; any imbalance between the two cause diseases.
Through needling, the acupuncturist balances the energies effecting a cure.


Meridians/ channels?
The energy or CHI circulating through the entire body regulates the circulation of the blood ingestion and the auto protection of the organism.

It also flows along the meridian. The meridians are passages or channels in the body where the vital energy CHI circulates.

The acupuncture points are locations where the Channels come to the surface and are easily accessible to needling, moxibustion and pressure.


Diagnosis/Chinese pulses?
Acupuncture believes that imbalance of the CHI or energy in the different meridians causes diseases. So it is important to locate where the meridians with excess or depletion of energy are.

In Acupuncture, successful diagnosis of a given disease is done by reading pulse.

Whereas Western medicine recognises only one type of pulse, Chinese medicine has 12 types of pulses. These pulses are felt in both radial arteries with three fingers next to each other and at the same time two different pressure strengths. Thus the state of 12 different organs are ascertained by taking the pulse.


Five Element Theory.
According to Indian Philosophy, every thing in this Universe belongs to any of the five elements, fire, water, earth, sky and air. This is the theory of 'Panchamahaboot'.

The traditional Chinese Philosophy has a similar theory, except that the five elements are wood, fire, earth, metal and water.

Each Yin organ is coupled to a Yang organ and they are identified with one of the five elements.

The Chinese believe that all these five elements are related in the destructive cycle called 'ko' as well as the generative cycle called 'sheng'.


Ko and Sheng Cycle?
In the diagram, the five cornered star represents the 'ko' cycle or destructive cycle and the outer continuous circle represents the 'sheng' cycle or constructive cycle.

In the 'Ko' cycle, the destructive pattern of the elements are shown. Fire destroys metal, metal destroys wood, wood destroys earth, and the earth destroys water.

In the 'Sheng' cycle, the constructive pattern of the elements are shown. Wood is fueled by fire which in turn yields earth. Metal can be mined from earth and when heated it liquefies. Water nourishes plants and it yields wood, and the constructive cycle thus continues.


Follow CHI or energy?
CHI can follow only the direction of the arrows and this fact has to be remembered during treatment whenever it is decided to divert energy from a channel showing excess to a channel which is deficient. Deficient channel should be properly needled to draw energy from the excess channel.

CHI or energy also follow a particular time sequence of maximum flow. In Acupuncture, each organ meridian has been allotted two hours of maximum energy flow.

For example, most of the acute asthma attacks occur between 3a.m to 5a.m. which is the time of optimum activity of the lung meridian. In disturbances of the liver function, sleeplessness or migraine headache occurs between 1a.m and 3a.m.

This two hour periodicity of optimum activity represents the best time for taking acupuncture action on the concerned meridian.


Channels in Acupuncture.
There are 14 main channels (meridian) running vertically up and down the surface of the body. Out of this, there are 12 organ channels in each half of the body (i.e. paired) and two midline (unpaired). These are connected by collaterals running horizontally and obliquely. In this net work vital energy circulates in a definite time-sequence.


Zang & Fu? (solid & hollow organs)
There are two categories of organs associated with the 12 organ channels.

'Zang' or solid organs having assimilative and storage functions. These are the heart, lungs, spleen, liver and kidneys.

'Fu' or hollow organs having eliminative functions. These are the stomach, large intestine, small intestine, Urinary bladder and gall bladder.

The 12 paired channels originate in these organs and are named after them. All channels originating from the Zang organs are YIN (negative) and those originating from the Fu organs are Yang (positive).

Chart showing cycle of CHI flow, Polarity and time of optimum flow.

Present of channels.
In the upper limbs there are three YIN channels starting from the chest and ending at the finger tips. They are the lung, pericardium and heart channels and three Yang channels, namely the large intestine, triple warmer and small intestine starting from the back of the fingers and ending on the face.

Three other Yang Channels, the stomach, gall bladder and urinary bladder, start from the face, extended along the trunk, back and sides of the leg to end at the toes. Three other Yin channels, the liver, spleen and kidney start from the toes, run over the medial (inside) aspect of the leg and thigh and end at the chest.

Two mid line meridians are the 'Conception vessel meridian' (Ren Mai) and the 'Governing vessel meridian' (Du mai). The conception vessel runs from the mid point of the perineum over the abdomen, navel and the chest and ends at the root of the tongue. The governing vessel starts from behind the anus, runs over the Sacrum, spinal column, nape of the neck passes over the head and front of the face, and ends in the mouth behind the upper lip.

The starting and end points of the meridians or channels on the fingers and toes are called 'Jing-Well points'. They are very useful pressure points in the emergencies and fainting attacks since changes of energy polarity occur here.


Materials of Acupuncture.
In ancient China, needles fashioned out of bamboo, animal horns and a variety of metals were used. Later silver and gold needles were in vogue. Nowadays the most commonly used needles are made of high tensile stainless steel with handles of silver. Some use steel needles with handles of copper gold or plastic (disposable).

There are several shapes and sizes of needles. Fili-form, press needles, cosmetic needle, triangular needle, hot needle, plum-blossom needle etc.


Materials..........





Functions of Materials?
Fili-form needles (a) : The most commonly used needles come in lengths varying from 0.5 inch to 8 inches and thickness of 26 to 32 gauge. One inch long and 30-gauge thick needles are in maximum use, mainly for body acupuncture.

Fili-form needles with double spiral handles (b) : are used for scalp acupuncture (Head needle -therapy). By and large, they are 11/2" long and 28-gauge thick.

Hot Needle : (c) A thick 18 gauge needle to treat conditions like ganglion and cystic goiter. It is heated over a lighter or a spirit lamp and suddenly poked in the above named swellings and then bandaged.


Triangular Needle (d) : A thick sharp-edged triangular needle for letting out blood at certain specific regions.

Press (intra-dermal) needles (e) : They are small button shaped needles with a point projecting from the center. In chronic stubborn diseases they are especially implanted in the ear and left in

Place for a few days with adhesive plaster.Cosmetic needles (f) : Thin, comma shaped needles for cosmetic problems like wrinkles, pimples, freckles etc.

Plum-Blossom Needle (g) : (5-7 star needle) This is a specially designed instrument which has 5-7 needles fixed at equal distances on a plastic head which in turn is attached to a long flexible handle.

Glass cups for cupping TherapyMoxa sticks, ginger, moxa powder for Moxibustion Acupressure pegsLighter, spirit, cotton etc.Electro stimulator: This apparatus is used to stimulate acupuncture needles with electricity. Various sophisticated models are available through out the world.

HOMEOPATHY

Homeopathy
What is it?
Homeopathy is a system of medicine, in which a drug and a disease that produce similar symptoms cancel each other out in some way thereby restoring the patients to, health.
This principle of 'Like can cure Like' forms the basis of Homeopathy.

It is named after the Greek words, ' Homeo' meaning similar and 'Pathos' meaning suffering or treatment by the same.

This system of healing was founded by a German doctor, Samuel Christian Hahnemann (1755).
In 1810, he set out the principles of Homeopathy in his book ' The Organon of Rationale Medicine'.

Why people like…..
It is popular among the people partly due to its remarkable healing capacity and partly because of the belief that its remedies are so refined that they don't cause any harmful results.

In Homeopathy remedy is chosen based on the symptoms as well the character and temperament of the patient. In short two persons with same illness may be offered different remedies based on their individual nature.

Origin of the knowledge.....
The principle of 'like can cure like' ( an illness should be treated by a substance capable of producing similar symptoms to those being suffered by the patient) dates back to the Greek physician Hippocrates (460-377 B.C) in the 5th century B.C.

He was the first person to think that disease was the result of natural forces, not divine influences. He believed that careful observation of the symptoms specific to an individual and the persons reactions and his own powers of healing should be taken into account before reaching a diagnosis and choosing a cure.

Hippocrates approach…..
Hippocrates known as the 'father of Medicine' had a collection of several hundred remedies. One of the best examples he provided of the principle of 'like curing like' was using the root of Veratrum album (white hellebore) in the treatment of cholera. In large doses this highly poisonous root causes violent purging that leads to severe dehydration, causing the same symptoms of cholera.

Modern approach.....
In the early 16th century, Swiss doctor Paracelus (1493-1541) found out that the causes of diseases were linked to external forces such as contaminated food and drink.

He also believed that a poisonous substance that causes disease could also cure the disease' if given in very small doses and that physicians should take into account the body's own natural ability to heal itself.

Here again the principle of 'Homeopathy' was advocated. But it did not gain popularity for another 300 years, until Homeopathy came into being.

Hahnemann Approach.....
In 1790, while translating 'A treatise on Materia Medica' by Dr. William Cullen, Hahnemann came across a passage about Peruvian Bark or Cinchona.

It stated that quinine which is a substance purified from the bark of the cinchona tree, was a good treatment for malaria because of its astringent qualities. This made no sense to Hahnemann who, as a chemist was aware that there were other much more powerful astringents that had no effect on malaria. Deciding to investigate further, he dosed himself with quinine and recorded his reactions in great detail.

Hahnemann & his experiment.....
He begun to develop the symptoms of malaria one after another, despite the fact that he actually did not have the disease. The symptoms recurred every time he took a dose of quinine and lasted for several hours. If he did not take any quinine, he had no symptoms. He repeated the doses of quinine, which he called 'provings' on people he knew well, noting the reactions in great detail.

He then repeated the process using other substances such as arsenic and belladonna under strict conditions. The 'provers' were not allowed to eat or drink anything that might confuse the results such as alcohol, tea, coffee and salty or spicy foods. The provers response varied, some showed a few mild symptoms to a particular substance, while others experienced vigorous reactions with a variety of symptoms.

Drug Picture.....
The symptoms that were most commonly found for each substance he called first line or keynote symptoms. Second line symptoms were less common and third line symptoms were rare.

The combination of symptoms made up a 'drug picture' for each substance. He continued to conduct experiments for 6 years, testing a wide range of substances.

He compiled the 'drug pictures' he had collected from his careful research, and started to test each substance on the sick to see whether they benefited from it.

Symptoms Picture.....
The patients were physically examined and thoroughly questioned about their symptoms, i.e., their general health, the way they lived and their outlook on life and what factors made them better or worse. Thus he build up a symptoms picture of each patient. Then he matched the individuals symptoms picture to the 'drug picture' of various substance. When he established the closest match, he would prescribe a remedy.

He found that the closer the match, the more successful the treatment. Thus a new system of medicine 'Homeopathy' was discovered.

Hanhemann….. Book
In 1776, Hanhemann published his book 'A new principle for ascertaining the curative powers of drugs and some examination of previous Principles', his first work on Homeopathy. In this book, he explained the key principle that, a drug taken in small amounts will cure the same symptoms it causes in large amounts.

Treatment and Remedies.....
In Homeopathy, illness is classified as acute or chronic.

In an acute illness, such as cold, a person becomes ill rapidly and after sometime it subsides with or without treatment.

But in chronic cases, a person suffers from continuous or recurrent illness, for example arthritis. The general trend of health is downwards.

How Prescribes Medicine.....
Homeopath prescribes medicines on the basis of the symptoms and the constitutional type of the patient.

A Homeopath decide the patients constitutional type by assessing a person's character and temperament, their fears, food preferences and general factors such as weather, temperature, seasons and time of the day which may worsen or improve physical condition.

Knowing the strength and weaknesses of an individual (i.e. his vital force) enables the Homeopath to prescribe the best remedy.

How remedies works.....
Homeopathic remedies help to speed up recovery, by stimulating the vital force, and strengthening it.

The remedies energize the vital force to rid the body of disease, helping it to return to its healthy state.

Sources of Remedie.....
Homeopathy medicines are made from plant, animal and mineral extracts and diluted in varying degrees in order to avoid unpleasant side effects.

The remedies range from toxic substances such as snake venom and mercury to common foods such as oats and onions.

These are available as lactose tablets, pillules, powder and granules.

Process of preparation - Soluble substance
The actual process of making remedies is very precise.

For remedies derived from soluble substances, such as animal or plant extracts the raw material is dissolved in an alcohol/water mixture that contains approximately 90 percent pure alcohol and 10 percent distilled water (this ratio may vary depending on the substance). This mixture is left to stand for 2- 4 weeks, shaken occasionally and then strained through a press. The resulting liquid is known as the mother tincture or tincture.

Process of preparation - Insoluble substance
Insoluble substances, such as gold, calcium carbonate and graphites, must first be made soluble by a process known as 'trituration', in which they are ground continually until they become soluble. They are then diluted and used in the same way as naturally soluble substances.

The remedies are so diluted that they no longer contain a single molecule of the original substance used to make them and yet they remain extremely effective.


Remedy Potencies.....
To produce different remedy potencies, the mother tincture is diluted in an alcohol/water mixture according to one of two scales, the decimal (*) and centesimal (c).

Between every stage of dilution the diluted tincture is shaken vigorously.

In the decimal scale the dilution factor is 1:10 and in the centesimal it is 1:100.

Example.....
To produce a 1c potency of the Alluim remedy, for example, one drop of the mother tincture is added to 99 drops of an alcohol/water mixture and shaken.

To produce a 2c potency, one drop of the 1c mixture is added to 99 drops of an alcohol/water mixture and succussed.

The number of a homeopathic remedy shows how may times it has been diluted and succussed, for example- 6c has been diluted and shaken 6 times. Beyond a 12c potency, a homeopathic remedy, is highly unlikely to retain a molecule of the original substance.

Development of Homeopathy.....
In 1831, there was a cholera outbreak in central Europe. Hahnemann's treatment with 'Camphor' was very successful. Dr. Frederick Foster Hervey Quin, follower of Hahnemann was one of many people cured of cholera by 'Camphor'. This enhanced his respect for Homeopathy, that in 1832 he set up a Homeopathic practice in London, where he later started the first Homeopathic hospital in 1849.

Homeopathy in US.....
Homeopathy was established in the US during the 1820's and gained a widespread following. Dr. Constantine Hering (1800-80) and Dr. James Tyler Kent (1849-1916) were two important American homeopaths who continued Hahnemann's work in proving remedies and also introduced new ideas and practices to homeopathy.

Laws of cure.....
The 'Laws of cure', devised by Dr. Hering explains how disease is cured in homeopathy. There are three basic laws of cure: a)symptoms move from the top of the body downwards; b) from the inside out and c) from the most important organs to the least important. Hering also believed that a cure occurred in reverse order to the onset of symptoms.

For example, a person generally feels better emotionally before the physical symptoms disappear.

Constitutional types.....
Dr. Kent observed that certain people reacted to certain remedies more strongly than to others. He maintained that people with similar body shapes and personalities tended to suffer from the same types of disease. He grouped people according to 'Constitutional types'.

For example, Natrum Mur types tended to be pear-shaped, had a dark complexion, were fastidious, kept to themselves, craved salt and suffered from constipation. High potency remedies were prescribed according to the patients constitutional type and physical symptoms, this came to be known as Classical Homeopathy .

Classical Homeopathy.....
Towards the end of the 19th century, Richard Hughes (1836-1902) an English homeopath questioned the theory of constitutional prescribing by Dr. Kent and insisted that only the physical symptoms of the patients should be taken into account while prescribing a remedy. He also advocated using lower potencies. This led to a split in Homeopathy, between the followers of Dr. Kent, who used high potencies and believed that a persons emotional characteristics and their physical symptoms should be taken into account and the followers of Dr. Hughes. This internal split, suppressed the practice of this system of medicine for sometime. But later Homeopathy experienced a resurgence throughout the world and Classical Homeopathy gained widespread recognition.

DNA

DNA
Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. The main role of DNA molecules is the long-term storage of information. DNA is often compared to a set of blueprints or a recipe, or a code, since it contains the instructions needed to construct other components of cells, such as proteins and RNA molecules. The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in regulating the use of this genetic information.

Chemically, DNA consists of two long polymers of simple units called nucleotides, with backbones made of sugars and phosphate groups joined by ester bonds. These two strands run in opposite directions to each other and are therefore anti-parallel. Attached to each sugar is one of four types of molecules called bases. It is the sequence of these four bases along the backbone that encodes information. This information is read using the genetic code, which specifies the sequence of the amino acids within proteins. The code is read by copying stretches of DNA into the related nucleic acid RNA, in a process called transcription.

Within cells, DNA is organized into structures called chromosomes. These chromosomes are duplicated before cells divide, in a process called DNA replication. Eukaryotic organisms (animals, plants, fungi, and protists) store their DNA inside the cell nucleus, while in prokaryotes (bacteria and archae) it is found in the cell's cytoplasm. Within the chromosomes, chromatin proteins such as histones compact and organize DNA. These compact structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed.

Biological functions
DNA usually occurs as linear chromosomes in eukaryotes, and circular chromosomes in prokaryotes. The set of chromosomes in a cell makes up its genome; the human genome has approximately 3 billion base pairs of DNA arranged into 46 chromosomes. The information carried by DNA is held in the sequence of pieces of DNA called genes. Transmission of genetic information in genes is achieved via complementary base pairing. For example, in transcription, when a cell uses the information in a gene, the DNA sequence is copied into a complementary RNA sequence through the attraction between the DNA and the correct RNA nucleotides.

Usually, this RNA copy is then used to make a matching protein sequence in a process called translation which depends on the same interaction between RNA nucleotides. Alternatively, a cell may simply copy its genetic information in a process called DNA replication. The details of these functions are covered in other articles; here we focus on the interactions between DNA and other molecules that mediate the function of the genome.

Replication
Cell division is essential for an organism to grow, but when a cell divides it must replicate the DNA in its genome so that the two daughter cells have the same genetic information as their parent. The double-stranded structure of DNA provides a simple mechanism for DNA replication. Here, the two strands are separated and then each strand's complementary DNA sequence is recreated by an enzyme called DNA polymerase. This enzyme makes the complementary strand by finding the correct base through complementary base pairing, and bonding it onto the original strand. As DNA polymerases can only extend a DNA strand in a 5′ to 3′ direction, different mechanisms are used to copy the antiparallel strands of the double helix. In this way, the base on the old strand dictates which base appears on the new strand, and the cell ends up with a perfect copy of its DNA.

History of DNA research
DNA was first isolated by the Swiss physician Friedrich Miescher who, in 1869, discovered a microscopic substance in the pus of discarded surgical bandages. As it resided in the nuclei of cells, he called it "nuclein". In 1919 this discovery was followed by Phoebus Levene's identification of the base, sugar and phosphate nucleotide unit. Levene suggested that DNA consisted of a string of nucleotide units linked together through the phosphate groups. However, Levene thought the chain was short and the bases repeated in a fixed order. In 1937 William Astbury produced the first X-ray diffraction patterns that showed that DNA had a regular structure.

In 1928, Frederick Griffith discovered that traits of the "smooth" form of the Pneumococcus could be transferred to the "rough" form of the same bacteria by mixing killed "smooth" bacteria with the live "rough" form. This system provided the first clear suggestion that DNA carried genetic information, when Oswald Avery, along with coworkers Colin MacLeod and Maclyn McCarty, identified DNA as the transforming principle in 1943. DNA's role in heredity was confirmed in 1952, when Alfred Hershey and Martha Chase in the Hershey-Chase experiment showed that DNA is the genetic material of the T2 phage.

In 1953, based on X-ray diffraction images taken by Rosalind Franklin and the information that the bases were paired, James D. Watson and Francis Crick suggested what is now accepted as the first accurate model of DNA structure in the journal Nature. Experimental evidence for Watson and Crick's model were published in a series of five articles in the same issue of Nature. Of these, Franklin and Raymond Gosling's paper was the first publication of X-ray diffraction data that supported the Watson and Crick model, this issue also contained an article on DNA structure by Maurice Wilkins and his colleagues. In 1962, after Franklin's death, Watson, Crick, and Wilkins jointly received the Nobel Prize in Physiology or Medicine. However, debate continues on who should receive credit for the discovery.

In an influential presentation in 1957, Crick laid out the "Central Dogma" of molecular biology, which foretold the relationship between DNA, RNA, and proteins, and articulated the "adaptor hypothesis". Final confirmation of the replication mechanism that was implied by the double-helical structure followed in 1958 through the Meselson-Stahl experiment. Further work by Crick and coworkers showed that the genetic code was based on non-overlapping triplets of bases, called codons, allowing Har Gobind Khorana, Robert W. Holley and Marshall Warren Nirenberg to decipher the genetic code. These findings represent the birth of molecular biology.