Vitamins and their history
Vitamins: - Organic compound
Vitamins are distinct from major components of food required in diet is small amount to perform specific biological fxn for normal maintenance of optimum growth and health whose absence cause specific deficiency dzs. E.coli is only organism which synthesizes all vitamins themselves. It is believed that during course of evolution the ability to synthesize vitamins was lost hence higher organism receiving it from their diet in small quantities because its degradation is relatively slow.
Vitamins are generally characterized into two groups:-
- Fat soluble
- Water soluble
General characteristics of vitamins
- Plants synthesizes all vitamins while few are synthesizes by animals
- All the cells of the body store vitamins to some extent.
- Vitamins when taken orally are effective.
- Vitamins are partly destroyed and are partly excreted.
- Vitamins are non antigenic.
- Human body can synthesize some vitamins.
- Synthetically-made vitamins are just as nutritionally good as natural vitamins.
Classification of Vitamins.
There are about 15 vitamins. Essential for humans they are classified as fat soluble (A, D, E, and K) and water soluble(c and B-group). The B-complex vitamins may be sub-divided into energy-releasing (B1, B2, B6, biotin etc.) and hematopoietic (folic acid and B12) Vitamins as per definition, are not synthesized in body. However bacteria of 9 us can produce some of vitamins required by man and animals. Some of the animals (e.g. rat, deer, etc.) eat their own feces. A phenomenon kolas coprophage. Fat Soluble Vitamins can be stored in liver and adipose tissue. They are not readily excreted in urine. Excess consumption of these vitamins (Particularly A and D) leads to their accumulation and toxic effect. Water soluble vitamins are not stored in body in large quantities (except B12).
History: - It was 1st recognized as essential nutrient factor by Elmer McCollum in 193 and then isolated from fish-lives oil by Holmes in 1917. Though its history was recorded way back in 500 BC when Hippocrates cured night blindness by prescribing patients ox liver (in honey) which is now known to have high quantity of vitamin A. It was 1st synthesized in 1947 by Miles.
Occurrence:- Liver oils of various fishes are richest natural sources of vitamin A. Shark and halibut having manwhereas(O-d-liver minimum fish liver ranging 2,000 to 1,00,000 I.U. per gram of vitamin A. the amount present in human liver is much less(500+1000 I.U. per gram). However polar bear contains extremely concn source of vitamin A. other source are butter, milk and egg and less extent kidney. In provitamin form (Yellow vegetables and fruits such as carrots, Pumpkins, cantaloupes, turnips, peppers, peas, Sweet potatoes papayas, Tomatoes, etc. Yellow corn is only cereal containing significant amt of carotene. Infant receive vitamin A through breast milk (colostrums). It is absent in vegetable fats and oil but added to margarine during its manufacture from these oils vitamin A originates in marine algae is passed through food chain to carnivores animal most animal food contains vitamin A well below toxic level except halibut liver oil which contain toxic amount.
Chemistry: - In recent years, the term vitamin A is collectively used to represent many structurally related and biologically active molecules. The term retinoid is often used to include the natural and synthetic form of vitamin Retino, retinal and retinoic acid is regarded as vitamin of vitamin A.
Retino (Vitamin A alcohol): It is primary alcohol containing B-inne ring containing two isoprenoid units in side chain-retino) is present in animal tissues as retinal ester with long chain fatty acids.
Retina (Vitamin A Oldehyde):- It is aldehyde form obtained by oxidation of Retinol. Retinal and rerinol are interconvertible.
Retinoic acid (Vitamin A acid):- It is produced by Oxidation of Retinal without reverse.
B Carotene (Provitamin A) it is found in plant foods. It is cleaved in intestine to produce two moles of retinal. B carotene possesses about one-sixth vitamin A activity compared to that of retinol.
ABSORPTION, TRANSPORT AND MOBILIZATION
Dietary retnyl esters are hydrolyzed by pancreatic of intestinal brush border hydrolyses in intestine, releasing retinol and free fatty acids. Carotenes are hydrolyzed by B-carotene 1s-1s- deoxygenate of intestinal cells to release 2 moles of retinal which is reduced to retinal. In intestinal mucosal cells, retinol is reesterified to long chain fatty acids incorporated into chylomicrons and transferred to lymph. The retinol esters of chylomicrons are taken up by liver and stored. As per needed Vitamin A is released from liver as free retinol, zinc playing major role in retinol mobilization. Retinol is transported in circulation by plasmaretional dinding protein (RBP: mol wt 21000) in association with pre-albumin. The retinol- RBP complex binds to specific receptors on cell membrane of peripheral tissue and enters the cells. Many cells of target tissues contain a cellular rational binding protein that carries tetinol to nucleus and binds to chromatin(DNA). It is here that rational exerts its function in manner analogous to that of a steroid hormone
Vitamin A is required for variety of function such as vision, proper growth and differentiation, reproduction and maintenance of epithelial cells.
Vitamin A and vision: - Biochemical function of vitamin A is process of vision was 1st elucidated by George weld (Nobel Prize 1968). The events occur in cyclic process klas Rhodesian cycle or weld's visual cycle.
The human eye has about 10million rods and 5 millions cones. The rods are in periphery while cones are at centre or retina. Rods are involved in dim light vision whereas lines are involved in color vision and bright light.
Wald’s Visual cycle
Rhodesian is conjugated protein present in rods. It contains 11-cist retinal and protein opsin. The alder Hyde group (Of retinal) is linked to E-amine group of lysine (of posing).
When expose to light, isomexization of ii-cist retinal to all Trans retinal occurs. This leads to conformational change in opsin which is responsible for generation of nerve impulse. The all-trans retinal is immediately isomerizes by retinal isomerasel of retinal is immediately isomerized by retinal isomerasel of rational epithelium) to 11-cis-retinal. This combines with posing to regenerate rhodopsin and complete visual cycle. However conversion of all trans-retinal to 11-cist retinal is incomplete. Therefore most of all-trans-retinal is transported to liver and converted to all-trans retinal by alcohol dehydrogenates. The all-Tran-retina of undergoes isomerization to 11-cis rational which is then oxidized to 11-cist retinal to participate in visual cycle.
Visual cascade and CGMP: - When light strike to retina no. of biochemical changes leading to membrane hyper polarization occurs resulting in genesis of nerve impuse. When a photon is absorbed by rhodopsin, metarhodopsin 2 is produced which activates transduction protein. This involves exchange of GTP for GDP on inactive transduction. The activated transduction activates cyclic GMP Phosphodiesterase. This enzyme degrades cyclic GIMP closer Na channels in membranes of rod cells. This result in hyperpolyarization which is excitatory response transmitted through neuron network to visual cortex of brain
DAT: - when person shifts from bright light to dim light rhodopsin stores depleted and vision is impaired for few minutes but rhodopsin is resynthesized and vision is improved. DAT is more in vitamin A deficient individual.
Color vision: - Color vision is governed by color sensitive pigments (porphuropsinlred), iodeosin (Green) 2 lyanopsin (blue)
RDA of Vitamin A in adults.
Man-1,000 retinol (3,500 IU)
Women 800 retinol (2, 5000)
One international unit (IU) equals to 0.3mg or retinol.
Vitamin A deficiently: - The deficiency systems of vitamin A are not immediate, since the hepatic stores can meet the body requirement for quite some time (2-4. Months.
Exophthalmia or xerosis: - It is major cause of blindness in childhood and few in adult. It is characterized by drying of eyes. Lachrymal gland is keratinized and ceases to produce tears. This makes external surface dry and dull ulcers develops and bacteria aren’t flushed which leads to swelling and sickness or eyelid. Causing exudation or blood causing infection of eye which when hot traded cause blindness.
Keratomalcia: - It is corneal dzs occurring maxmto pre-school children. Maximum to those suffering from kwashiorkor ESP after an episode of diarrhea or infection
Phrynoderma: it is skin lesion and is characterized by follicular hyperkeratosis.Other than this vitamin a deficiency also cause growth retardation, sterility in males, drying of skin formation of urinary stones, hair loss
Hypervitamosis A: - Excessive consumption of vitamin A leads to toxicity. Symptoms being dermatitis, enlargement of liver, skeletal decalcification tenderness of long bone, loss of wt, hair irritability joints pains etc
Vitamins a level is elevated in vitamin A toxicity. Free rational and retinol bound to plasma lipoprotein is actually harmful to the body. It is believed that toxicity occurs when retinol binding capacity of retinol binding protein exceeds.
However higher consumption of B-carotene has no toxic effect moreover it helps to decrease heart attack, skin and lung cancers risks.
History: - the existence of vitamin D was shown by Elmer McCollum in 1922 who found that cod liver oil was effective in preventing rickets, a dzs induced in rat by providing low calcium diet. Vitamin D is often called as antirachitic factor. It is also kolas sunshine vitamin as its provitamin form present in human skin is easily converted to active form by irradiation with ultraviolet rays. Vitamin D was isolated by august (1931) who named it calciferol. Vitamin D is a fat soluble vitamin which resembles sterols in S TR and function like a hormone.
Chemistry: - Ergocalciferol (vitamin D2) is formed from ergo sterol and is present in plant cholecalcirerol (vitamin D3) is found in animals. Both the sterols are similar in STR except that ergocalciferal has an additional methyl group and a double bond.