Biochemistry 8 - Vitamins PDF

Vitamins: Biochemical Roles Vitamins “VITAMIN” means “vital for life” VITAMINS are *Micronutrients (*Nutrients required in very small amounts - mg or µg), which are necessary for everyday healthy functioning of the body VITAMINS cannot be synthesised in the body So they have to be su...

Vitamins: Biochemical Roles Vitamins “VITAMIN” means “vital for life” VITAMINS are *Micronutrients (*Nutrients required in very small amounts - mg or µg), which are necessary for everyday healthy functioning of the body VITAMINS cannot be synthesised in the body So they have to be supplied thru’ diet Vitamins are necessary components of healthy diets and play important roles in cellular metabolism Although these substances occur in only very small amounts within cells, they are critically important Their absence is usually manifested as some deficiency disease What are vitamins? Non-caloric organic nutrients Facilitators – help body processes proceed; digestion, absorption, metabolism, growth etc. Some appear in food as precursors or provitamins The term vitamin was first used to describe the “vital amine,” thiamine (B1), which is needed to prevent beriberi disease (once a common disease among people who depended upon white rice for their main source of food)  Vitamins are relatively small molecules that function most often as coenzymes Coenzyme: a small molecule that works with an enzyme to promote the enzymes activity - a coenzyme that is very tightly or even covalently bound to the enzyme protein is called a prosthetic group A complete, catalytically active enzyme together with its bound coenzyme is called a holoenzyme The protein part of such an enzyme is called the apoenzyme or apoprotein  Humans must consume at least 12 vitamins in their diet, because we lack the ability to synthesize them A well-balanced diet from a variety of food sources usually provides all these vitamins. However, many people supplement their diet with extra vitamins Most vitamins are chemically altered in some way so they can function in the body Some vitamins are measured in I.U.s (International Units), which is a measure of biological activity This measuring system is needed because these vitamins have several natural forms that have different activities on an equal weight basis Other vitamins are measured on the basis of weight (mg or μg) Vitamins - US FDA In the United States, the Food and Drug Administration (FDA) sets “Daily Reference Intakes,” which are the highest amounts of daily vitamins that are needed by 95% of the population Dietary Reference Intakes (DRI) and Recommended Dietary Allowances (RDA) The DRIs are actually a set of four reference values: Estimated Average Requirements (EAR), Recommended Dietary Allowances (RDA), Adequate Intakes (AI), and Tolerable Upper Intake Levels, (UL) that have replaced the 1989 Recommended Dietary Allowances (RDAs) http://www.nal.usda.gov/fnic/etext/000105.html Vitamins - categories Vitamins are categorized into two groups: Water soluble: The “B”-vitamins (Pantothenic acid, Biotin, Folic acid…) Vitamin C Fat-soluble Vitamins: Vitamins A, D, E, K Water vs. Fat soluble vitamins Cannot be stored in body - regular supply needed Excess is excreted in urine - no danger of toxic levels Unstable to heat and light, leach into cooking liquids Can be stored in body - regular supply not needed Can accumulate to toxic levels if large amounts ingested Fairly stable at normal cooking temperatures Water vs. Fat soluble vitamins Water soluble vitamins Found in vegetables, fruit and grains, meat Absorbed directly into the blood stream Not stored in the body and toxicity is rare Alcohol can increase elimination, smoking, etc. cause decreased absorption Dissolve in water Subject to cooking losses Generally readily excreted 50-90% of B vitamins are absorbed Marginal deficiency more common Function as a coenzyme In energy metabolism B - vitamins Do not give people energy, like energy yielding nutrients, but help to burn this fuel This class contain 8 B vitamins, each work as coenzyme Must be present in every cell continuously for the proper cell function Thiamin (B1) Riboflavin (B2) Niacin (B3) Pantothenic Acid(B5) Pyridoxine (B6) Catalysts in biochemical pathways! Biotin (B7) Folic Acid (B9) Cyanocobalamine (B12) Water soluble Vitamins 12 B-1 Thiamin Important in: Deficiency: Producing energy from carbohydrates Loss of appetite nerve function Weakness & Feeling tired appetite It is thought that thiamin can be Insomnia useful for motion sickness in air growth and sea travel, and that this Loss of weight Muscle function vitamin also repels insects Depression Sources: when excreted through the Heart & Gastrointestinal skin. In autism management. problems Fish Thiamin should be taken with the B group vitamins and beriberi Liver manganese Legumes Who is at risk? Nuts Malnourished Whole grain or enriched breads and Alcoholics cereals Malabsorption B-1 is nontoxic even at high dosages Beriberi disease Beriberi: Overview, Causes, and Symptoms (healthline.com) 15 B-2 Riboflavin Important in: Deficiency: energy production Itching and burning eyes carbohydrate, fat, and protein metabolism Cracks and sores in mouth and formation of antibodies and red blood lips cells Dermatitis cell respiration maintenance of good vision, skin, Oily skin nails, and hair Who is at risk? Sources: Malnourished Milk eggs Alcoholics meats People with sickle cell anemia leafy green vegetables enriched grains B-2 is nontoxic at recommended levels 17 B-3 Niacinamide & Niacin Important in: Deficiency: energy production Pellegra (4 D’s) maintenance of skin and tongue Dermatitis improves circulation maintenance of nervous system Diarrhea health of the digestive track Dementia Lowers cholesterol when used in Death higher doses Sources: Who is at risk? Milk eggs Most people get plenty of B-3 meats from their diet because it is leafy green vegetables added to white flour enriched grains In very high doses some times (“niacin flush”) occurs Pelagra disease Pellagra: Pictures, Symptoms, Causes, and Treatment (healthline.com) B6 - pyridoxine B9 - folate B-12 - cobalamine B5 and B7 Vitamin C Ascorbic acid (Toxic to viruses, bacteria, and some malignant tumor cells) Antioxidant Protects you body from free radicals Helps form connective tissue (Collagen) Helps healing of wounds Helps in absorbing iron Keep your gums healthy Immunity Prevention of heart disease Prevention of cancer  Harmful effects in larger doses: Deficiency: (over 1000mg/ dose) Weight loss Diarrhea fatigue and joint Avoid chewable tablets (may pain cause damage to teeth) scurvy (bruising Since Vitamin C is water- easily, bleeding soluble excess amounts that gums, and the body does not need will tendency for bones be excreted, but larger doses can cause some problems to fracture) reduced resistance Sources: to colds and Leafy Greens vegetables infections Citrus Fruits slow healing of wounds and fractured bones  Scurvy on the St. Lawrence River: Vitamin C “Some did lose all their strength, and could not stand on their feet… Others also had all their skins spotted with spots of blood of a purple colour: then did it ascend up to their ankles, knees, thighs, shoulders, arms, and necks. Their mouths became stinking, their gums so rotten, that all the flesh did fall off, even to the roots of the teeth, which did also almost all fall out. - Jacques Cartier, 1536 James Lind, a Scottish physician published a paper in 1747 that clearly linked the prevention of scurvy to the consumption of citrus fruits in the diet. Following his suggestions, The Royal Navy issued lime rations to sailors, resulting in their nickname, “limeys.” Seven years earlier, a British task force of six ships lost almost 1,000 sailors to scurvy during an extended sea voyage. Scurvy Scurvy: Symptoms, Risk Factors, Treatment, Recovery, and More (healthline.com) 29 Structures of Water-soluble Vitamins Water-soluble Vitamins Fat soluble vitamins Found in the fats and oils of food Absorbed into the lymph and carried in blood with protein transporters = chylomicrons *Stored in liver and body fat and can become toxic if large amounts are consumed Fat-soluble vitamins Note: There is a major error in this table. What is it? The function and deficiency of A and E are switched. The fat-soluble vitamins share some structural and solubility similarities. Fat-soluble Vitamins Vitamin A – Our visual pigment: Vitamin A Vitamin A - Retinol Vitamin A helps with our vision Too much Vitamin A can cause serious side effects, hence larger doses of this pure vitamin are controlled by prescription An excellent natural source of vitamin A is the pigment, β-carotene The body splits this molecule into two molecules of vitamin A. A person can consume so much β-carotene that their skin turns orange, but the body only converts enough of it into vitamin A to meet its needs, hence avoiding an excess of this vitamin and its deleterious effects Note: Eating carrots can actually help some low-light [“night”] vision problems by supplying vitamin A in the form of β-carotene Vitamin A from beta-Carotene Vitamin D Vitamin D acts as a Vitamin D hormone, helping regulate the uptake of calcium from the intestines by promoting the synthesis of calcium- binding protein in the mucosal cells. Deficiency of this vitamin causes “rickets,” a condition of low levels of calcium, which results in soft and pliable bones, leading to bending and distortion. Rickets Rickets: Symptoms, Diagnosis, and Treatments (healthline.com) Vitamin D Vitamin D is sometimes called the “sunshine vitamin.” This is due to its unique biosynthetic route that requires UV light to complete its synthesis. Vitamin D – The Sunshine Vitamin By law, milk sold in the USA must be fortified with Vitamin D. It is obtained primarily from irradiated yeast extracts. Fish oils are also a good source of vitamin D. You can synthesize your own vitamin D by simply exposing your skin to UV light. (This is always a good excuse to get some sunshine.) Russian children in the artic tundra were often afflicted with rickets, due to lack of sunshine and/or adequate dietary sources (e.g., availability of fish oils). Years ago, (and still today?) the Russian government sent UV lights to the elementary schools in this region and required students to absorb UV light from these lamps to help synthesize vitamin D and reduce the occurence of rickets. (A National Geographic story a few years ago showed a picture of the students getting their daily dose of UV light) Ultraviolet Bath, Russia (nationalgeographic.com) Vitamin E Vitamin E helps promote male virility in rats and enhances birth rates. Hence, many believe it must therefore be important for humans… Its role in humans is not completely understood, hence it is difficult to determine a minimum recommended daily intake. However, premature infants fed on formulas low in vitamin E often develop a form of hemolytic anemia that can be corrected by vitamin E supplementation. Most manufacturers of infant formulas fortify their preparations with this vitamin.