Biochemistry Lecture Notes on Vitamins PDF

E C K B3 P B6 Ca BIOCHEMISTRY B2...

E C K B3 P B6 Ca BIOCHEMISTRY B2 Mg VITAMINS B1 Na A Fe Dr: Wael Sobhy Darwish K Zn PhD Biochemistry 52 ENERGY Per 100g/kcal Lect-1  Introduction Biochemistry can be defined as the science concerned with the study of chemical reactions that occurs in living organisms Vitamins are organic nutrients that are required in small quantities for a variety of biochemical functions and which generally cannot be synthesized in the body and must be supplied by the diet.  Vitamins also assist in the formation of hormones, blood vessels, nervous system chemicals, and genetic materials. They generally act as catalysts, combining with proteins to create metabolically active enzymes that are essential for life reactions. Classification of vitamins  Difference between water& fat-soluble vitamins Water soluble vitamins Fat soluble vitamins Solubility Water soluble Fat soluble Absorption Simple Along with lipids Storage *No storage Stored in liver Excretion Excreted Not excreted Excess intake Nontoxic Toxic Deficiency Manifests rapidly Manifests slowly Treatment Regular dietary supply Single large dose Fat-soluble vitamins Vitamin A ❖ Vitamin A occurs in two forms in food: ❑ Retinoids (preformed vitamin A, found only in foods of animal origin). ❑ Carotenoids: ▪ Found in plants ▪ Comprise carotenes and related compounds ▪ known as provitamin A, as they can be cleaved to yield retinaldehyde, retinol, and retinoic acid. ▪ The α, β, and γ carotenes are the most important provitamin A carotenoids.  VITAMIN A FUNCTION ▪ Vision. ▪ Antioxidant. ▪ Regulation of gene expression & and tissue differentiation. ▪ Essential for health and growth ▪ Essential for the formation and calcification of bone ▪ More important is that retinoic acid is a gene regulator during early fetal development. Women who are or who may become pregnant should not consume vitamin A in amounts above the safe upper limit (3,000 micrograms) because birth defects are a risk Vitamin A toxicity A dose of more than 200 mg of retinol or retinal, or chronic consumption of more than 40 mg/day causes nonspecific signs of toxicity. Signs and symptoms of chronic vitamin A toxicity can include: Gastrointestinal symptoms: hepatomegaly, splenomegaly Neurological symptoms: severe headache Dermatological symptoms: rash, thin and coarse hair, itch, and dry or cracked lips Musculoskeletal: weakness, easy fractures  VITAMIN A DEFICIENCY Night blindness. Xerophthalmia. Infections. keratinization of skin. Impairment of immune responses.  Vitamin D Vitamin D is not strictly a vitamin since it can be synthesized in the skin, and under most conditions that is its major source. Only when sunlight is inadequate is a dietary source required.  Vitamin D is present in two forms Ergocalciferol (vitamin D2), Found in plants. Cholecalciferol (vitamin D3), Found in animal tissues. Vitamin D is present in only a few natural foodstuffs, including liver, egg yolk, and saltwater fish The main function of vitamin D is in the regulation of calcium absorption Synthesis of vitamin D Vitamin D is synthesized in the skin by the action of ultraviolet radiation. The product of this reaction, cholecalciferol (vitamin D3), has no biological activity. It must first be hydroxylated to 25-hydroxycholecalciferol in the liver, followed by hydroxylation to 1,25- dihydroxycholecalciferol (calcitriol) in the kidney. The function of vitamin D  Vitamin D deficiency Rickets (in children). Osteomalacia (in adults). Osteoporosis: bone loss disease Hypervitaminosis D, which is caused by overuse of vitamin D supplements, leads to hypercalciuria, and metastatic calcification (abnormal calcification of soft tissues)  Toxicity of vitamin D Vitamin D toxicity most often occurs from taking supplements Symptoms of toxicity: Anorexia, Weight loss Irregular heart beat Hardening of blood vessels and tissues due to increased blood levels of calcium, potentially leading to damage of the heart and kidneys  Vitamin E Vitamin E is the generic descriptor for two families of compounds: The tocopherols and The tocotrienols. the most active is D-α-tocopherol. The main function of vitamin E is as a chain-breaking, free radical-trapping antioxidant in cell membranes and plasma lipoproteins.  Vitamin E is an antioxidant and scavenger of free radicals. It protects membranes, fat depots, and lipoprotein from lipid peroxidation. vitamin E has a reputation for reducing the risk of cancer, coronary heart disease, and age-related degenerative diseases. Vitamin E deficiency leads to Hemolytic anemia. Good sources for vit E include vegetable oils, various oil seeds, and wheat germ. Vitamin E is non toxic Vitamin K Vitamin K forms: -In plants as phylloquinone (K1). - In intestinal bacterial flora as menaquinone (k2). -A synthetic form of vitamin K, menadione. It is required for synthesis of blood clotting proteins. Deficiency signs: blood loses its power to clot or the time needed for clotting is longer and serious hemorrhages can result from slight wounds or bruises. Sources: green leafy forages, fish meal, liver, soybeans, rumen and intestinal synthesis, and the synthetic compounds.