Science of Nutrition Study Guide for Final Chapters 10 11 12 and 1 Cole Friedes Chapter 10 Nutrients Involved in Antioxidant Function Antioxidants compounds that protect cells from the damage caused by oxidation Loss of electrons is called oxidations because it s fueled by oxygen Gaining electrons is called reduction Normally during redox reactions two atoms with unpaired electrons immediately pair up making new stabilized molecules When a molecule is formed and the valence electrons do not pair and there is a lone electron the molecule is called a free radical or a reactive oxygen species Free radicals can often be formed during metabolism when oxygen accepts a free electron Also formed from when our immune systems fight infections Free Radicals can Destabilize other Molecules Free radicals are the seductive outsider to the paired electrons They will exert a powerful attraction and steal an electron from stable compounds in turn generating more free radicals This produces a chain reaction If free radical forms in lipid membrane they destroy the integrity of the membrane making it no longer hydrophobic and they lose the ability to regulate fluid and nutrients Antioxidants Work by Stabilizing Free Radicals 3 main ways antioxidants function 1 Antioxidant vitamins work independently by donating their electrons or hydrogen molecules to FRs to stabilize them 2 Antioxidant minerals act as cofactors within complex antioxidant enzyme systems that convert the FRs to less damaging substances that can be excreted Examples of enzyme systems are superoxide dismutase converts FRs to hydrogen peroxide Catalase removes hydrogen peroxide from body Glutathione peroxidase removes hydrogen peroxide from body and stops productions of FRs 3 Other compounds like beta carotene and phytochemicals stabilize FRs and prevent damage to cells and tissues A Profile of Nutrients that Function as Antioxidants Vitamin E One of the fat soluble vitamins therefore dietary fats carry it from the intestines through the lymph system and eventually into the cells Part of both LDLs and VLDLs transported throughout the body by those lipoproteins There are two separate families of vitamin E tocotrienols and tocopherols All of the tocotrienols are inactive in the body Tocopherols are the active forms RDA is expressed in terms of ALPHA tocopherol in mg day The primary function of vitamin E is as an antioxidant It donates an electron to FRs stabilizing them and preventing them from destabilizing other molecules One it is oxidized it is either excreted from the body or recycled back into active vitamin E Since Vit E is a fat soluble vitamin it mainly protects polyunsaturated fatty acids and LDLs from being oxidized therefor lowering risk for cardiovascular disease CVD Also is critical antioxidant in protecting the cells in our lungs The RDA of vitamin E is 15 mg of ALPHA tocopherol this is to prevent erythrocyte hemolysis or the rupturing of the red blood cells which can lead to anemia Vitamin E food sources are vegetable oils and the products made from them almost all oils Deficiencies of vitamin E are uncommon because it is a fat soluble vitamin Can affect muscle coordination vision and speech impairments Vitamin C 2 main forms of vitamin C ascorbic acid and dehydroascorbic acid Vitamin C is most known for its role in preventing scurvy It does this by assisting in the synthesis of collagen Collagen is a protein that is a critical component of all connective tissues in the body Without adequate vitamin C the body cannot synthesize enough collagen and hemorrhaging and bleeding can occur Vitamin C is an extremely important antioxidant in the extracellular fluid It donates electrons to FRs Protects LDL cholesterols and enhances immune system function Vitamin C regenerates vitamin E after it ahs been oxidized This occurs when ascorbic acid donates electrons to vitamin E radicals becoming dehydroascorbic acid Dehydroascorbic acid is then reduced back to ascorbic acid by GSH glutathione which is a tri peptide composed of glycine cysteine and glutamic acid The RDA for vitamin C is 90 mg per day for men and 75 mg per day for women The UL is 2000 mg per day Smoking increases the need for vitamin C in the body Good food sources of vitamin C are fruits and vegetables the best sources Because vitamin C is water soluble typically we excrete any excess High amounts can be bad in people with hemochromatosis which causes accumulation of excess iron in the body Scurvy is really the only vitamin C deficiency Very rare in developed countries Beta Carotene It is not considered an essential nutrient but it is a provitamin which are inactive forms of vitamins that the body cannot use until they are converted to their active form Beta carotene is the precursor and inactive form of vitamin A Part of a phytochemical class called carotenoids which is a group of plant pigments 1 molecule of beta carotene can be split to form two molecules of active vitamin A Functions of BC as an antioxidant are enhancing the immune system protecting the skin from the sun s UV rays and protecting our eyes and preventing vision damage Since it is not an essential nutrient there is no RDA for BC but it is recommended to have 6 10 mg a day anyway Fruits and vegetables are and anything that is orange is a good source of the provitamin There are no toxic effects of too much BC but it can turn your skin orange or yellow There are also no known deficiencies Vitamin A Much more than an antioxidant nutrient Critical to vision and to the growth and differentiation of cells Three active forms of vitamin A in the body Retinol is the alcohol form Retinal is the aldehyde form Retinoic Acid is the acid form Collectively called the retinoids Vitamin A is presented in RAE or retinol activity equivalents Vitamin A functions as an antioxidant by scavenging FRs and protecting LDLs from oxidation Vit A affects our sight in two ways It enables us to react to changes in the brightness of light It enables us to distinguish between different wavelengths of light i e see color In the retina retinal Combines with a protein called opsin to from rhodopsin a light sensitive pigment Rhodopsin is found in the rod cells which are cells that react to dim light and interpret B W images When light hits the retina the rod cells go through a bleaching process Rhodopsin is split into retinal and opsin Both of these molecules change shape which triggers the brain to receive a nerve impulse that interprets
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