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The role of vitamins in metabolism. Dr. Samah Kotb Nasr Eldeen. What is a vitamin???. A vitamin is both : An organic compound (contains carbon ). An essential nutrient, the body cannot produce enough of on its own, so it has to get it (tiny amounts) from food. Classification of vitamins.
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The role of vitamins in metabolism Dr. Samah Kotb Nasr Eldeen
Avitamin is both: • An organic compound (contains carbon). • An essential nutrient, the body cannot produce enough of on its own, so it has to get it (tiny amounts) from food.
Types of vitamins 1) Fat-soluble vitamins are stored in the fat tissues of our bodies, as well as the liver. Fat-soluble vitamins are easier to store than water-soluble ones, and can stay in the body as reserves for days, some of them for months. • Fat-soluble vitamins are absorbed through the intestinal tract with the help of fats (lipids) • Vitamins A, D, E and K are fat-soluble. 2) Water-soluble vitaminsdo not get stored in the body for long - they soon get expelled through urine. • Water-soluble vitamins need to be replaced more often than fat-soluble ones. • Vitamins C and all the B vitamins are water-soluble.
Introduction • Water-soluble vitamins are alike in that, with the exception of B12, they can be supplied by plants in the diet. These vitamins are not stored in the body for very long and therefore need to be consumed regularly. • Primarily the water-soluble vitamins serve as coenzymes in metabolic reactions. • The majority of the water-soluble vitamins are 'B' vitamins and these play a major role in energy metabolism.
Thiamin : vitamin form Pyrimidine ring Thiazole ring Thiamin pyrophosphate: coenzyme form
Function • Thiamin, or vitamin B1, plays a major role in carbohydrate metabolism. • Thiamin acts as a coenzyme along with phosphorus in important cellular reactions such as decarboxylation and transketolation. • Thiamin pyrophosphate (TPP),a coenzyme, allows pyruvate to enter the citric acid cycle (Krebs' cycle) to produce energy for cellular functions. TPP acts in fat synthesis by transketolation, providing glyceraldehydefor the conversion of glucose to fat. • Thiamin is thought to be involved in neurotransmission and nerve conduction
Absorption and excretion • Thiamin is absorbed quite easily in the jejunum and ileum. • Thiamin is transported to the liver in the blood. • High amounts of thiamin are stored in the skeletal muscles, heart, liver, kidneys, and brain. Approximately one-half of the thiamin is stored in the muscles.
Clinical conditions • Thiamin deficiency, called beribericaused by dietary deficiency of thiamine (vitamin B1 ). It affects the nerves to the limbs, producing pain, paralysis), • Insufficient thiamin can result in diminished alertness and reflexes, apathy, and fatigue. • Thiamin deficiency affects lipogenesis and results in degeneration of the lipid myelin sheaths covering the nerve fibers. • Clinical symptoms include pain and prickly sensations, and in a severe deficiency paralysis can result.
Gastrointestinal symptoms include indigestion, constipation, gastric atony, deficient hydrochloric acid secretion, and anorexia. • Thiamin deficiency also can weaken the heart muscle, leading to cardiac failure and edema in the extremities. • A disease called Wernicke-Korsakoff syndrome results in ocular motor signs, ataxia, and derangedmental function. Most patients with Wernicke-Korsakoff syndrome are alcoholics, but few alcoholics actually develop the disease.
Food Sources • Sources include beef, liver, yeast, whole grains, enriched grains, and legumes. yeast, sunflower seeds, brown rice, asparagus, cauliflower, potatoes, oranges and eggs.
Thiamin therapy • Thiamin therapy is used in the treatment of alcoholics. • Malnutrition often develops from alcohol and a poor diet, leading to neurological disorders. Infections increase cellular energy requirements and therefore thiamin requirements.
Home work Complete the following:- 1) Thiamin deficiency, called ……………disease caused by dietary deficiency of thiamine (vitamin B1 ). It affects the ............, producing ..............., ...................... 2) ………………………………, a coenzyme, allows …………. to enter the citric acid cycle (Krebs' cycle) to produce energy for cellular functions. TPP acts in fat synthesis by ……………….., providing …………………… for the conversion of ……………….. to ……………. .
True or False and rewrite the false :- • 1) Water-soluble vitamins are alike in that, with the exception of B12 ( ). • 2) Infections decrease cellular energy requirements and therefore thiamin requirements ( ).
Function • Riboflavin, or B2, is a constituent of enzymes called flavoproteins. • Flavin mononucleotide(FMN) and flavin-adenine dinucleotide(FAD) are vital in the respiratory chain of cellular energy metabolism. • FMN is used in deamination, which is the process of removing the amino group from amino acids. • FAD is used in the deamination of glycine, an amino acid. FAD is also involved in the oxidation of some fatty acids.
Absorption and excretion of Riboflavin
Absorption and excretion • Riboflavin is absorbed in the proximal small intestine. • In human blood, riboflavin is primarily bound to proteins. The immunoglobulin IgG binds readily to the free form of riboflavin. • Conversion of riboflavin to coenzymes occurs in cellular cytoplasm of tissues, primarily in the small intestine, liver, heart, and kidney. • Lactoflavin is contained in the milk of lactating women. • Little riboflavin is actually stored in the body; it is excreted through the urine.
Mechanism of action as cofactors and flavoproteins • Flavoproteins play important roles in the electron transport chain . • Decarboxylationof pyruvate and α-ketoglutaraterequires FAD. • FAD is required to the production of pyridoxic acid from pyridoxal(vitamin B6) • The primary coenzyme form of vitamin B6 (pyridoxal phosphate) is FMN dependent.
FAD is required to convert retinol (vitamin A) to retinoic acid. • Synthesis of an active form of folate is FADH2 dependent. • FAD is required to convert tryptophan to niacin (vitamin B3). • Reduction of the oxidized form of glutathione (GSSG) to its reduced form (GSH) is also FAD dependent
Clinical conditions • Riboflavin deficiency, also known as ariboflavinosis, occurs in areas with long periods of low intake. • Deficiency is usually accompanied by deficiency of other B vitamins. • Symptoms include the inflammation and breakdown of tissue, swollen and cracked lips, swollen tongue, and red, itchy eyes. • Newborn infants with jaundice that are treated with phototherapy have shown signs of riboflavin deficiency. • Toxicity is non-existent. Excess riboflavin is readily excreted in the urine.
Food Sources • Milk is the most abundant source of riboflavin. Other sources include organ meats, whole grains, enriched grains, and broccoli. • Asparagus, bananas, persimmons, okra, chard, cottage cheese, yogurt, eggs, fish, and green beans. • Riboflavin is easily lost in cooking due to its water solubility.
Home work Complete the following:- 1)…………….. is the most abundant source of riboflavin. Other sources include …………., …………, …………., and ……… 2)……………… is contained in the milk of lactating women.
True or False and rewrite the false :- • 1) Riboflavin is easily lost in cooking due to its fat solubility ( ). • 2) FAD is required to convert retinol (vitamin A) to retinoic acid ( ).
