Science of Nutrition Study Guide for Final: Chapters 10, 11, 12, and 1Cole FriedesChapter 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 AntioxidantsVitamin 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.
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