Vitamins

Organic compound required in small amounts in the diet to maintain normal metabolic functions.

Vitamin foods

The term vitamine (1911) was changed to vitamin when it was realized that not all vitamins are amines (i.e., not all contain nitrogen).

Many vitamins act as or are converted to coenzymes. They neither provide energy nor are incorporated into tissues.
Water-soluble vitamins (vitamin B complex, vitamin C) are excreted quickly.
Fat-soluble vitamins (vitamin A, vitamin D, vitamin E, and vitamin K) require bile salts for absorption and are stored in the body.
The normal functions of many vitamins are known.
Deficiency of specific vitamins can lead to diseases (including beriberi, neural tube defect, pernicious anemia, rickets, and scurvy).

Harmones in Human Body

Pituitary Gland (hypophysis)

Endocrine gland lying on the underside of the brain that plays a major role in regulating the endocrine system.

·        The anterior pituitary lobe secretes six hormones

·         that play specific roles in stimulating production of cortisol and androgens by the adrenal cortex (corticotropin),

·          growth of eggs and sperm (follicle-stimulating hormone), production of progesterone and testosterone (luteinizing hormone),

·         linear growth in children and bone maintenance in adults (growth hormone), milk production (prolactin), and production of thyroid hormone (thyrotropin).

·          The posterior lobe stores and releases two hormones, oxytocin and vasopressin, from nerve cells in specialized regions of the hypothalamus that control pituitary function.

·          These hormones stimulate uterine contraction and milk secretion (oxytocin) and blood pressure and fluid balance (vasopressin).

1.Androgen

• Any of a group of hormones that mainly influence the development of the male reproductive system.
• The main and most active androgen is testosterone, produced by cells in the testes.
•  Androgens produced in smaller quantities, mainly by the adrenal gland but also by the testes, support the functions of testosterone.
•  Androgens cause the normal changes of puberty in boys' bodies and then 
• influence sperm-cell formation, sexual interest and behaviour, and male pattern baldness. Females produce trace quantities of androgens, mostly in the adrenal glands, as well as in the ovaries.

2.Progesterone

·        Steroid hormone secreted by the female reproductive system that functions mainly to regulate the condition of the endometrium (see uterus), preparing it to accept a fertilized egg.

·        If the egg is not fertilized, the level of progesterone drops, the uterine lining breaks down, and menstruation ensues.

·         If the egg is fertilized (see pregnancy), the placenta produces progesterone, whose effects include preparing the mammary glands for lactation. Many forms of oral contraception use a synthetic progesterone.

3.Testosterone

·        Any of a group of hormones that mainly influence the development of the male reproductive system.

·        The main and most active androgen is testosterone, produced by cells in the testes.

·         Androgens produced in smaller quantities, mainly by the adrenal gland but also by the testes, support the functions of testosterone.

·         Androgens cause the normal changes of puberty in boys' bodies and then influence sperm-cell formation, sexual interest and behaviour, and male pattern baldness.

·          Females produce trace quantities of androgens, mostly in the adrenal glands, as well as in the ovaries.

4.oxytocin

5.vasopressin

6.prolactin

Oncology-Cancer

Cancer (Uncontrolled multiplication of abnormal cells)

• Cancerous cells and tissues have abnormal growth rates, shapes, sizes, and functioning.
•  Cancer may progress in stages from a localized tumour (confined to the site of origin) to direct extension (spread into nearby tissue or lymph nodes) and metastasis (spread to more distant sites via the blood or lymphatic system).
• This malignant growth pattern distinguishes cancerous tumours from benign ones. Cancer is also classified by grade, the extent to which cell characteristics remain specific to their tissue of origin. Both stage and grade affect the chances of survival.
• Genetic factors and immune status affect susceptibility. Triggers include hormones, viruses, smoking, diet, and radiation.
• Cancer can begin in almost any tissue, including blood (see leukemia) and lymph (see lymphoma). When it metastasizes, it remains a cancer of its tissue of origin. Early diagnosis and treatment increase the chance of cure.
•  Treatment may include chemotherapy, surgery, and radiation therapy. See also bladder cancer; breast cancer; carcinogen; colorectal cancer; Kaposi sarcoma; laryngeal cancer; lung cancer; ovarian cancer; pancreatic cancer; prostate cancer; skin cancer; stomach cancer; uterine cancer.

Tumour or neoplasm

Mass of abnormal tissue that arises from normal cells, has no useful function, and tends to grow.

• Cell abnormalities may include increased size or number or loss of characteristics that differentiate their tissue of origin.
• Cells in malignant tumours (see cancer) have a distorted size, shape, and/or structure. Less differentiated cells tend to grow faster.
•  Malignant tumours invade tissues locally and spread (metastasize) in blood or lymph: the stronger the tendency to metastasize, the more malignant the tumour. Tumours may not cause pain until they press on or invade nerves.
•  Both benign and malignant tumours can press on nearby structures, block vessels, or produce excess hormones, all of which can cause death. Benign tumours remain as a solid mass that can be removed by surgery if accessible; they can consist of various tissues and may become malignant; malignant tumours, though they may remain quiescent for a time, never become benign.

Leukemia

Cancer of blood-forming tissues with high levels of leukocytes.

• Radiation exposure and hereditary susceptibility are factors in some cases.
•  In acute leukemias, anemia, fever, bleeding, and lymph-node swelling develop rapidly. Acute lymphocytic leukemia, found mostly in children, was once over 90% fatal in six months. Drug therapy can now cure more than half these children. Acute myelogenous (granulocytic) leukemia, found mostly in adults, has frequent remissions and recurrences, and few patients survive long.
• Chronic myelogenous leukemia most often begins in the 40s; weight loss, low fever, weakness, and other symptoms may not develop immediately. Chemotherapy helps the symptoms but may not prolong life.
• Chronic lymphocytic leukemia, mostly in the elderly, may be inactive for years. Survival rates are better than in myelogenous leukemia; most deaths are caused by infection or hemorrhage.

Lymphoma

Any of a group of malignant diseases (see cancer) that usually start in the lymph nodes or lymphoid tissues.

• The two major types
•  Hodgkin disease and non-Hodgkin lymphoma, each have several subtypes.
• Diagnosis of either type requires biopsy, usually from the lymph nodes. Non-Hodgkin lymphomas may be diffuse (widespread) or nodular (concentrated in nodules); nodular lymphomas generally develop more slowly.

Prostate Cancer

Malignant tumour of the prostate gland.

Prostate cancer commonly occurs in men over age 50. Symptoms include frequent or painful urination, blood in the urine, sexual dysfunction, swollen lymph nodes in the groin, and pain in the pelvis, hips, back, or ribs. The likelihood of developing prostate cancer doubles if there is a family history. Treatment may include surgery, radiation therapy, hormone therapy, chemotherapy, or a combination of two or more of these approaches.

Mastectomy

• Surgical removal of a breast, usually because of breast cancer.
• If the cancer has spread, radical mastectomy may remove surrounding tissue and/or nearby structures, including chest muscles and lymph nodes. Modified radical mastectomy leaves at least the main chest muscle, has an equally high survival rate, and makes reconstruction easier. Simple mastectomy is removal of the breast only. Lumpectomy is removal of the tumour only.

• Breast Cancer
• Malignant tumour in a breast, usually in women after menopause.

Risk factors include family history of breast cancer, prolonged menstruation, late first pregnancy (after age 30), obesity, alcohol use, and some benign tumours.

Most breast cancers are adenocarcinomas. Any lump in the breast needs investigation because it may be cancer. Treatment may begin with radical or modified mastectomy or lumpectomy (in which only the tumour is removed), followed by radiation therapy, chemotherapy, or removal of the ovaries or adrenal glands.

Hodgkin disease or lymphoreticuloma

Most common malignant lymphoma.

It starts with local, painless swelling of lymph nodes and sometimes of the spleen, liver, or other organs, followed by weight loss and weakness.

Diagnosis can be confirmed only by biopsy, usually from a lymph node. The cause remains unknown.

Treatment with chemotherapy, radiation, or both depends on the stage of the disease. More than 90% of patients diagnosed early can be cured, as can many with advanced disease.

Chemotherapy

Treatment of diseases, including cancer, with chemicals.

• Some cancer drugs interfere with cancer-cell division or enzyme processes.
•  However, they have serious side effects, attacking some healthy cells and reducing resistance to infection.
• Certain steroids are used to treat breast cancer and prostate cancer, leukemia, and lymphomas. Derivatives of plants such as periwinkle (vincristine, vinblastine) and yew (taxol) have been found effective against Hodgkin disease, leukemia, and breast cancer.

Pancreatic Cancer

Malignant tumour of the pancreas.

Risk factors include smoking, a diet high in fat, exposure to certain industrial products, and diseases such as diabetes and chronic pancreatitis.

 Pancreatic cancer is more common in men. Symptoms often do not appear until pancreatic cancer is advanced; they include abdominal pain, unexplained weight loss, and difficulty digesting fatty foods.

Surgery, radiation therapy, chemotherapy, or some combination of these may be used to treat the disease.

Source:Britannica Encyclopedia

 Proenzyme

Any of a class of proteins that are secreted by cells and are inactive precursors of enzymes.

ProEnzyme

Transformation into active enzymes occurs as one or more peptide bonds in the zymogen are cleaved. Examples include trypsinogen and chymotrypsinogen, secreted by the pancreas and converted by proteolysis in the small intestine into the active enzymes trypsin and chymotrypsin; and numerous coagulation factors.

VACCINE

Preparation containing either killed or weakened live microorganisms or their toxins, introduced by mouth, by injection, or by nasal spray to stimulate production of antibodies against an infectious agent.

Vaccine

This confers immunity to that agent, since the B lymphocytes remain sensitized to it and respond to later infection by producing more antibodies. The first vaccine, against smallpox, was introduced by Edward Jenner in 1798. Vaccines have been developed against diseases caused by bacteria (e.g., typhoid, whooping cough, tuberculosis) and by viruses (e.g., measles, influenza, rabies, poliomyelitis). Effectiveness varies, and a small percentage of people have adverse reactions. Those with immunodeficiency disorders should not receive live vaccines.

Zooplanktum

     Small floating or weakly swimming animals that drift with water currents and, with phytoplankton, make up the planktonic food supply on which almost all oceanic organisms ultimately depend (see plankton).

Zooplankton

Included are many animals, from single-celled radiolarians to the eggs or larvae of herrings, crabs, and lobsters. Permanent plankton (holoplankton), such as protozoans and copepods, spend their lives as plankton. Temporary plankton (meroplankton), such as young starfish, clams, worms, and other bottom-dwelling animals, live and feed as plankton until they become adults.

Vitamin K

VitaminK

Any of several fat-soluble compounds essential for the clotting of blood.

A deficiency of vitamin K in the body leads to an increase in clotting time. In 1929 a previously unrecognized fat-soluble substance present in green leafy vegetables was found to be required for coagulation of the blood; its letter name comes from the Danish word koagulation. A pure form was isolated and analyzed structurally in 1939; several related compounds having vitamin-K activity have since been isolated and synthesized. The form of vitamin K that is important in mammalian tissue is of microbial origin. A synthetic vitamin K precursor called menadione is used as a vitamin supplement.

Source: Britannica encyclcopedia

Vitamin E

Vitamin E or Tocopherol

Fat-soluble organic compound found principally in certain plant oils and leaves of green vegetables.

Vitamin E acts as an antioxidant in body tissues and may prolong life by slowing oxidative destruction of membranes. Certain rodents require it for normal reproduction. Besides uses in foods and in nutritional research and supplements, it is used to retard rancidity in fats, especially vegetable oils.

Source: Britannica encyclcopedia

Vitamin D

Vitamin D

Any of a group of fat-soluble alcohols important in calcium metabolism in animals to form strong bones and teeth and prevent rickets and osteoporosis.

It is formed by ultraviolet radiation (sunlight) of sterols (see steroid) present in the skin. The most important of these sterols are 7-dehydrocholesterol, formed by metabolic processes in animals, and ergosterol, present in vegetable oils. The action of sunlight on the skin converts these two compounds, respectively, to cholecalciferol (vitamin D3) and ergocalciferol (vitamin D2). Vitamin D is added to margarine, milk, and cereals for the benefit of those who may not get enough sunlight in winter. As little as 5 micrograms each day appear adequate for children. Because the body cannot excrete it, prolonged high intake can cause a toxic reaction including fatigue, nausea, and abnormal calcium accumulation.

Source: Britannica encyclcopedia

Vitamin C

Vitamin  C or ascorbic acid

Water-soluble organic compound important in animal metabolism.

Most animals produce it in their bodies, but humans, other primates, and guinea pigs need it in the diet to prevent scurvy. It is essential in collagen synthesis, wound healing, blood-vessel maintenance, and immunity. Some studies have found a moderate benefit of vitamin C in reducing the duration and severity of the common cold. It works as an antioxidant in the body and is used as a preservative. It is easily destroyed by oxygen. Excellent sources are citrus fruits and fresh vegetables.

Source: Britannica encyclcopedia

Vitamin B complex

Vitamin B complex

Water-soluble organic compounds with loosely similar properties, distribution in natural sources, and physiological functions.

Most are coenzymes, and all appear essential to the metabolic processes of all animal life. They include thiamin (B1), riboflavin (B2), niacin, vitamin B6, pantothenic acid, folic acid, biotin, and vitamin B12 (cobalamin); some authorities also include choline, carnitine, lipoic acid, inositol, and para-aminobenzoic acid. Vitamin B6 is needed for metabolism of amino acids and prevention of skin and nerve disorders. Vitamin B12 prevents pernicious anemia and is involved in nucleic-acid synthesis, fat metabolism, and conversion of carbohydrate to fat. The B complex vitamins are particularly abundant in cereal grains, meats, nuts, and some fruits and vegetables.

Thiamin or vitamin B1

Organic compound, part of the vitamin B complex, necessary in carbohydrate metabolism.

It carries out these functions in its active form, as a component of the coenzyme thiamin pyrophosphate. Its molecular structure includes a substituted pyridine ring and a thiazole ring. Thiamin is found most abundantly in whole cereal grains and certain other seeds. Deficiency leads to beriberi.

Riboflavin or vitamin B2

Yellow, water-soluble organic compound, abundant in whey and egg white.

It has a complex structure incorporating three rings. Green plants and most microorganisms can synthesize it; animals need to acquire it in their diet. It exists in combined forms as coenzymes and functions in the metabolism of carbohydrates and amino acids. A syndrome resembling pellagra is thought to result from riboflavin deficiency. See also flavin.

Niacin or nicotinic acid vitamin B3

Water-soluble vitamin of the vitamin B complex, essential to growth and health in animals, including humans.

It is found in the body only in combined form as a coenzyme, nicotinamide adenine dinucleotide (NAD), which is involved in the metabolism of carbohydrates and the oxidation of sugar derivatives and other substances. One of the most stable vitamins, it survives most cooking and most preserving processes. It is widely found in dietary sources, especially lean meat. Deficiency causes pellagra. It is used as a drug to reduce high cholesterol levels in the blood.

Biotin
Organic compound, part of the vitamin B complex, essential for growth and well-being in animals and some microorganisms.

A carboxylic acid with two rings in its structure, it includes nitrogen and sulfur atoms as well as carbon, hydrogen, and oxygen. It functions in the formation and metabolism of fats and carbohydrates. It is widely distributed in nature and is especially abundant in egg yolk, beef liver, and yeast. A biotin deficiency can be induced by consuming large amounts of raw egg white, which contains a protein (avidin) that combines with biotin and makes it unavailable. Biotin is needed to synthesize fatty acids and convert amino acids to glucose in the body.

Source: Britannica encyclcopedia

Folic acid or folate

Organic compound essential to animal growth and health and needed by bacteria as a growth factor.

Part of the vitamin B complex, folic acid is necessary for synthesis of nucleic acids and formation of the heme component of hemoglobin in red blood cells. To prevent neural tube defects in babies, it should ideally be taken by women starting at least a month before conception. Dietary folate sources include leafy and dark green vegetables, citrus fruits, cereals, beans, poultry, and egg yolks, but free folic acid is available only in supplements. Low intake leads to folic acid deficiency anemia.

Source: Britannica encyclcopedia

Vitamin A

Vitamin A also called retinol

Fat-soluble alcohol, most abundant in fatty fish and especially in fish-liver oils.

It is not found in plants, but many vegetables and fruits contain beta-carotene (see carotene), which is readily converted in the body to vitamin A. It functions directly in vision, especially night vision. A derivative, retinaldehyde, is a component of the visual pigments, including rhodopsin, in the retina. Humans require vitamin A in very small amounts. Unlike carotenes, it is toxic in large amounts and is readily destroyed by exposure to heat, light, or air.

Source: Britannica encyclcopedia

Vitamins

Vitamins

Organic compound required in small amounts in the diet to maintain normal metabolic functions.

The term vitamine (1911) was changed to vitamin when it was realized that not all vitamins are amines (i.e., not all contain nitrogen). Many vitamins act as or are converted to coenzymes. They neither provide energy nor are incorporated into tissues. Water-soluble vitamins (vitamin B complex, vitamin C) are excreted quickly. Fat-soluble vitamins (vitamin A, vitamin D, vitamin E, and vitamin K) require bile salts for absorption and are stored in the body. The normal functions of many vitamins are known. Deficiency of specific vitamins can lead to diseases (including beriberi, neural tube defect, pernicious anemia, rickets, and scurvy). Excess amounts, especially of fat-soluble vitamins, can also be dangerous: e.g., too much vitamin A causes liver damage, an effect not seen with beta-carotene, which the body converts into vitamin A. Several vitamins are now known to support the immune system. Most vitamins are adequately supplied by a balanced diet, but people with higher requirements may need supplements.

Source: Britannica encyclcopedia

Type of Glucose

Carbohydrate
Any member of a very abundant and widespread class of natural organic compounds that includes sugars, starch, and cellulose.

They are commonly classified as monosaccharides (simple sugars; e.g., glucose, fructose), disaccharides (2-unit sugars; e.g., sucrose, lactose), oligosaccharides (3–10 or so sugars), and polysaccharides (large molecules with up to 10,000 monosaccharide units, including cellulose, starch, and glycogen). Green plants produce carbohydrates by photosynthesis. In most animals, carbohydrates are the quickly accessible reservoir of energy, and oxidation (see oxidation-reduction) of glucose in tissues supplies energy for metabolism. Many (but by no means all) carbohydrates have the general chemical formula Cn(H2O)n. The carbon (C) atoms are bonded to hydrogen atoms (−H), hydroxyl groups (−OH; see functional group), and carbonyl groups (−C=O), whose combinations, order, and geometric arrangement lead to a large number of isomers with the same chemical formula but different properties. The class is further enlarged because each isomer has various derivatives: uronic acids, sugars with an oxidized group; sugar alcohols, sugars with a reduced group; glycosides, compounds of sugars with other molecules containing a hydroxyl group; and amino sugars, sugars with an amino group (see amino acid).

Monosacchride
Any of the simple sugars that serve as building blocks for carbohydrates.



They are classified based on their backbone of carbon (C) atoms: Trioses have three carbon atoms, tetroses four, pentoses five, hexoses six, and heptoses seven. The carbon atoms are bonded to hydrogen atoms (−H), hydroxyl groups (−OH; see functional group), and carbonyl groups (−C=O), whose combinations, order, and configurations allow a large number of stereoisomers (see isomer) to exist. Pentoses include xylose, found in woody materials; arabinose, found in gums from conifers; ribose, a component of RNA and several vitamins; and deoxyribose, a component of DNA. Important hexoses include glucose, galactose, and fructose. Monosaccharides combine with each other and other groups to form a variety of disaccharides, polysaccharides, and other carbohydrates.



Polysaccharide
Any of a large class of long-chain sugars composed of monosaccharides.

Because the chains may be unbranched or branched and the monosaccharides may be of one, two, or occasionally more kinds, polysaccharides can be categorized in various ways. Cellulose, starch, glycogen, and dextran are all polysaccharides of glucose, with different configurations. Pectins are composed of a galactose derivative, chitin of a glucose derivative. Connective tissues, joint fluid, and cartilage contain two-component polysaccharides, including heparin. See also oligosaccharide.


Galactose

Organic compound, a monosaccharide, chemical formula C6H12O6.

It is usually found in nature combined with other sugars, for example, in lactose, in polysaccharides, and in glycolipids, carbohydrate-containing lipids that occur in the brain and other nervous tissues of most animals. It has uses in organic synthesis and in medicine.


Fructose

levulose fruit sugar

Organic compound, one of the simple sugars (monosaccharides), chemical formula C6H12O6.

It occurs in fruits, honey, syrups (especially corn syrup), and certain vegetables, usually along with its isomer glucose. Fructose and glucose are the components of the disaccharide sucrose (table sugar); hydrolysis of sucrose yields invert sugar, a 50:50 mixture of fructose and glucose. The sweetest of the common sugars, fructose is used in foods and medicines.



Source: Britannica encyclcopedia

Type of Bacteria

Nitrifying bacteria
Small group of oxygen-requiring bacteria that use nitrogen as an energy source.

Nitrifying bacteria

These microorganisms are important in the nitrogen cycle as converters of soil ammonia to nitrates, compounds usable by plants. The nitrification process requires two distinct groups: bacteria that convert ammonia to nitrites, and bacteria that convert nitrites to nitrates. In agriculture, irrigation with dilute solutions of ammonia results in an increase in soil nitrates through the action of nitrifying bacteria. See also denitrifying bacteria.

Denitrifying Bacteria
Soil microorganisms whose action results in the conversion of nitrates in soil to free atmospheric nitrogen, thus exhausting soil fertility and reducing agricultural productivity.



Denitrifying Bacteria

Without denitrification, earth's nitrogen supply would eventually accumulate in the oceans, since nitrates are highly soluble and are continuously leached from the soil into nearby bodies of water. See also nitrifying bacteria.

Coliform Bacteria
Rod-shaped bacteria usually found in the intestinal tracts of animals, including humans.

Coliform Bacteria

Coliform bacteria do not require but can use oxygen, and they do not form spores. They produce acid and gas from the fermentation of lactose sugar. Their presence in the water supply indicates recent contamination by human or animal feces. Chlorination is the most common preventive water treatment

Sheathed Bacteria
Group of bacteria found widely in nature in slow-running water.

Sheathed Bacteria

Many species are attached to underwater surfaces. They are characterized by a threadlike, branching arrangement of cells enclosed in a sheath. The sheaths of some are variously encrusted with iron or manganese oxides, depending on the water. One of the best-known is a common species, Sphaerotilus natans; in polluted water it has thin, colourless sheaths, and in unpolluted water containing iron it has yellow-brown, iron-encrusted sheaths that often grow into long slimy tassels.

Sulfer Bacteria
Any of a diverse group of bacteria that are capable of metabolizing sulfur and its compounds and are important in the sulfur cycle.

sulfer Bacteria

Members of the genus Thiobacillus, widespread in marine and terrestrial habitats, react with sulfur to produce sulfates useful to plants; in deep ground deposits they generate sulfuric acid, which dissolves metals in mines and corrodes concrete and steel. Desulfovibrio desulficans reduces sulfates in waterlogged soils and sewage to hydrogen sulfide, a gas with the common rotten-egg odour.


Budding Bacteria
Group of bacteria that reproduce by budding.

Budding Bacteria

Each bacterium divides following unequal cell growth; the mother cell is retained, and a new daughter cell forms. In budding, the cell wall grows from one point on the cell rather than throughout the cell; this type of growth permits the development of more complex structures and processes. Most budding bacteria are aquatic and can attach to surfaces by their stalks; some are free-floating.

Source: Britannica encyclcopedia

Membrane

Membrane
In biology, the thin layer that forms the outer boundary of a living cell or of an internal cell compartment.

Membrane

The outer boundary is the plasma membrane, and the compartments enclosed by internal membranes are called organelles. Biological membranes have a dual function: separation of vital but incompatible metabolic processes conducted in the organelles; and passage of nutrients, wastes, and metabolic products between organelles and between the cell and the outside environment. Membranes consist largely of a double layer of lipids in which are embedded large proteins, many of which transport ions and water-soluble molecules across the membrane. See also cytoplasm, eukaryote.

Source: Britannica encyclcopedia

Prokaryote

Prokaryote
Any cellular organism that lacks a distinct nucleus.

Prokaryote

Bacteria (including blue-green algae, or cyanobacteria) are prokaryotes; all other organisms are eukaryotes. Prokaryotic cells lack a nuclear membrane and most of the components of eukaryotic cells. The cytoplasm includes ribosomes that carry out protein synthesis and a double-stranded DNA chromosome, usually circular. Many prokaryotes also contain additional circular DNA molecules called plasmids. The flagella are distinct from those of eukaryotes in design and movement.

Source: Britannica encyclcopedia

Protein

Protein
Any of numerous organic compounds, complex polymers of amino acids that are involved in nearly every aspect of the physiology and biochemistry of living organisms.

Protein

Twenty different amino acids are common to proteins, linked in chains of hundreds to thousands of units. An active protein molecule has three important levels of structure: primary (the amino acid sequence), determined by the genes; secondary (the geometric shape, often a helix), determined by the angles of the covalent bonds between and within amino acids; and tertiary (the looped and folded overall shape), determined largely by attraction between oppositely charged groups (and repulsion between like charged groups) on amino-acid side chains and especially by hydrogen bonding. The tertiary structure, which can be globular or sheetlike with ridges, crevices, or pockets, often holds the key to a protein's biological activity. Proteins can serve, e.g., as structural material (as in connective tissue and hair; see collagen; keratin), as enzymes and hormones, as transporters of essential substances such as oxygen (see hemoglobin), as antibodies, or as regulators of gene expression. Some proteins are simple (amino acids only), some conjugated (see conjugation) to other groups, often vitamins or metal atoms needed in tiny amounts in the diet (see coenzyme; cofactor). Rhodopsin and hemoglobin are conjugated proteins. Proteins may be covalently linked to other atoms or molecules, as to sugars (glycoproteins), phosphate groups (phosphoproteins), or sulfur (sulfoproteins). Proteins are an essential human nutrient, obtained from both plant and animal foods. Their greatest commercial use is in food products; they are also employed in adhesives, plastics, and fibres.

Source: Britannica encyclcopedia

Cynobacteria

Cynobacteria
or blue-green algae

Any of a large group of prokaryotic, mostly photosynthetic organisms.

Cynobacteria

Though classified as bacteria, they resemble the eukaryotic algae in many ways, including some physical characteristics and ecological niches, and were at one time treated as algae. They contain certain pigments, which, with their chlorophyll, often give them a blue-green colour, though many species are actually green, brown, yellow, black, or red. They are common in soil and in both salt and fresh water, and they can grow over a wide range of temperatures, from Antarctic lakes under several metres of ice to Yellowstone National Park's hot springs in the U.S. Cyanobacteria are often among the first species to colonize bare rock and soil. Some are capable of nitrogen fixation; others contain pigments that enable them to produce free oxygen as a by-product of photosynthesis. Under proper conditions (including pollution by nitrogen wastes) they can reproduce explosively, forming dense concentrations called blooms, usually coloured an opaque green. Cyanobacteria played a large role in raising the level of free oxygen in the atmosphere of early Earth.

Source: Britannica encyclcopedia

Protozoan

Protozoan
Any of a group of small (usually microscopic) single-celled protists.

Art:Representative protozoans. The zooflagellate Trypanosoma brucei is the causative agent of …

Protozoan

 * Representative protozoans. The zooflagellate Trypanosoma brucei is the causative agent of …
They are found in most soils, fresh water, and oceans. While most are solitary individuals, various colonial forms exist. The taxonomic relationships of protozoans to one another and to other protists continue to be revised. The smallest known protozoans are tiny blood parasites less than 2 microns long; the largest may be 16 mm long and visible to the naked eye. Protozoan shapes vary, but all share such eukaryotic features as lipid-protein membranes and membrane-enclosed vacuoles and organelles (see eukaryote). They show wide variation in modes of movement, nutrition, and reproduction. Various classification systems exist to group the protozoans. The major phyla include Sarcomastigophora (flagellated forms and forms possessing cytoplasmic extensions called pseudopodia), Ciliophora (ciliated forms), and Apicomplexa, Microspora, and Myxozoa (spore-producing forms). Apicomplexa and Microspora are sometimes included in the single phylum Sporozoa. Commonly known protozoans include dinoflagellates, amoebas, and paramecia (see paramecium).

Source: Britannica encyclcopedia