Introduction: Vitamin A, in its various forms, is an essential component of mammalian health. In addition to its well-documented role in vision, Vitamin A contributes to several other important biological functions including nuclear transcription, skin cell differentiation, growth, and immunity. As animals are not capable of synthesis, vitamin A and its metabolites (collectively know as the retinoids) must be obtained through the diet (Goodman 1984). Two major forms of vitamin A are found in food: retinol and carotenoids. All of these fat-soluble vitamins contain two distinct structural features that contribute to all of their activity. The first is a β-ionone ring to which the second critical motif, an isoprenoid chain, is attached. Retinol, the major circulating form of vitamin A, is not biologically active. Rather, it serves as the metabolic precursor for the active retinoids (Chapman 2012). Oxidation at C-15 converts retinol to the visual pigment retinal, while subsequent oxidation of the aldehyde produces retinoic acid, which is involved in gene transcription (Figure 1). It is important for the body to maintain plasma retinol homeostasis to serve as a precursor reservoir for these active retinoids. Mobilization of Vitamin A from the liver and its circulation to peripheral tissues is a highly regulated process. Delivery without appreciable loss of retinol requires it be bound tightly to plasma retinol-binding protein (RBP). RBP, first described by Goodman and colleagues in 1968, is synthesized in the endoplasmic reticulum of hepatocytes and contains a single binding site for only all-trans-retinol (Goodman 1980). Upon secretion into the plasma, Retinol-RBP circulates as a complex with a larger protein, transthyretin (TT... ... middle of paper ... ... retinol release may function near the membrane surface at near-neutral bulk pH (Ptitsyn et.al. 1993). Conclusion Through its specific interaction with trans retinol, RBP allows this vital nutrient to circulate without appreciable loss. In addition to ligand-binding, RBP interacts with the carrier protein transthyretin (TTR). This protein complex prevents the loss of RBP through glomerular filtration and is also suggested as a vehicle for specific interactions with alleged cell-surface receptors that mediate retinol uptake. In conclusion, retinol-binding protein provides a comprehensive model for the role of proteins as carrier molecules. Structural features such as a characteristic up-and-down beta barrel, disulfide bonds, salt bridges and a hydrophobic core are essential in influencing the complex interactions that are essential to RBP function.
Heaney RP. The vitamin D requirement in health and disease. J Steroid Biochem Mol Biol. 2005;97(1-2):13-19.
Vitamin B12 is an essential water soluble vitamin that must be carefully regulated to prevent deficiency related complications in the nervous, gastrointestinal, and cardiovascular systems (e). This review begins with a discussion of B12 absorption and role as a cofactor for L-methylmalonyl-CoA mutase and methionine synthase (e). Laboratory findings are interpreted along with associated disease conditions. Finally, assay methods are discussed including blood smear and complete blood count, B12 competitive-binding immunoenzymatic assay, homocysteine tandem mass spectrometry, methylmalonic acid liquid chromatography tandem mass spectrometry, and the Schilling test.
Duerbeck, N., & Dowling, D. (2012). Vitamin A: Too much of a good thing?. Obstetrical & Gynecological Survey, 67(2), 122-128. doi:10.1097/OGX.0b013e318244c52d
The data presented in this table supports the conclusion of Purdy et al. (2005) that the inclusion of cholesterol to the CHO cell membranes will result in significant changes to the membrane, confirming the established function of cholesterol as a regulator of membrane fluidity.
Vitamin D3 (ergocalciferol) originates from 7-dehydrocholesterol, a precursor of cholesterol when synthesized in the skin.3
Noble, J., & Chaudhary, V. (2010). Diabetic retinopathy. Canadian Medical Association Journal, 182(15), 1646. doi: 10.1503/cmaj.090536.
Vitamin B12 is an essential nutrient that plays an important role in DNA synthesis and nerve function. It is contained in high amounts in animal derived foods such as milk, eggs, and meat. The vitamin is stored in the liver long-term. Individuals with vegetarian, vegan, or other forms of restricted diet may develop the condition after approximately 6 months as liver stores of vitamin B12 become depleted. Some individuals develop the condition due to autoimmune destruction of cells in the stomach that produce intrinsic factor. Intrinsic factor is necessary for proper absorption of vitamin B12 in the small intestine.
The body can manufacture only vitamin D; all others must be derived from the diet. Lack of them causes a wide range of metabolic and other dysfunctions. In the U.S., since 1940, the Food and Nutrition Board of the National Research Council has published recommended dietary allowances (RDA) for vitamins, minerals, and other nutrients.
Vitamin E in all its forms, functions predominantly as an antioxidant by protecting cells from free radicals in the body. Vitamin E works as an antioxidant by donating a hydrogen atom from a hydroxyl group to a free radical within the body. Vitamin E also plays a role in immune system function and protects cell membranes and regulation of gene expression. Vitamin E has been studied to uncover other medical usages, including prevention or treatment of many health conditions [1].
When one hears the three words: vitamins, nutrients, and minerals, they think of one thing-being healthy and noticing what your intake is daily. Nutrition is all about vitamins and nutrients. Firstly, vitamins are an organic compound required by the body in small amounts of metabolism, to protect health, and for proper growth of children. Vitamins also assist in the formation of hormones, blood cells, nervous systems chemicals, and genetic material. There are 13 well-identified vitamins. Some examples of the 13 well-identified vitamins are: A, D, E, and K-fat contained foods, B, C-consumed immediately. A well known and commonly used in commercials for orange juice vitamin is vitamin C. Vitamin C or ascorbic acid is important in the synthesis and maintenance of connective tissues. The lack of vitamin C will result in a sickness called scurvy. Scurvy harms the gums, mucous membranes, and the skin. Another well-known vitamin and is also used to commercial to give more information about this beverage is the vitamin in milk. The vitamin in milk is vitamin D. If you do not drink milk and obtain this vitamin, your bones and teeth will become soft and weak. Lacking one or more of the 13 well-identified vitamins will cause sickness and weakness to your body. Secondly, nutrients are how the body assimilates certain compounds. Nutrients are classified in 5 major groups: proteins, carbohydrates, fats, vitamins, and minerals. One of the five nutrients is carbohydrate. The carbohydrate group principally consists of sugar, starch, dextrin, cellulose, and glycogen. In more basic terms, carbohydrates are sugars needed by human and other living organisms. Some types of foods that contain carbohydrates would be candies, ice cream, fruit juice, soda, chocolate bars etc. Lastly, vitamins are connected to minerals. Minerals are also a very important part of a healthy person. There are 11 major groups of minerals. They are: calcium, chromium, copper, iodine, iron, magnesium, manganese, phosphorous, potassium, selenium, and zinc. All these terms look very familiar if one has taken chemistry. These are the elements of our world. One of the more common minerals that most people have heard of is calcium. Calcium also helps with the structure and strength of teeth and bones. Vitamins and minerals work together to help humans maintain a healthy body. For example, vitamin D works with calcium to help for and maintain the strength of teeth and bones.
Transferring dietary lipids (fats) - Lipids as well as lipid soluble are similar substance vitamins which are captivated meaning absorbed from the diet and are passed to the blood within the lymphatic system to a certain extent rather than by the venous drainage of the small intestine.
Vitamin D can often be obtained with two different methods. The main method is the conversion of 7-dehydrocholesterol in the skin into Vitamin D3 via sun exposure to absorb ultraviolet B radiation with a wavelength of 290-315nm (Holick 2007). The other method, is through consumption in diets through plants in the form of Vitamin D2; or fatty fishes, supplements or fortified vitamin D products in the form of Vitamin D3 (Lavie, Lee & Milani 2011). Vitamin D undergoes hydroxylation twice; first with the enzyme 25-hydroxylase to form 25-hydroxyvitamin D (Calcidiol) (Al Mheid et al. 2013). Then, Calcidiol is converted to the most active form of Vitamin D, 1,25-dihidroxyvitamin D Hormone (Calcitriol) with the help of renal 1--hydroxylase in the kidney (Al Mheid et al. 2013). Vitamin D2 and D3 are relatively similar since share the same hydroxylation pathway to produce Calcitriol (Tripkovic 2013), however, D3 has shown to have a greater influence on Calcidiol levels and thus more effective in maintaining Vitamin D health (Heaney et al. 2011).
If we examine the detailed structures of many transmembrane proteins, we see that they often have three different domains, two hydrophilic and one hydrophobic .(fig 1&2) A hydrophilic domain (consisting of hydrophilic amino acids) at the N-terminus pokes out in the extracellular medium, a hydrophobic domain in the middle of the amino acid chain, often only 20-30 amino acids long, is threaded through the plasma membrane, and a hydrophilic domain at the C-terminus protrudes into the cytoplasm. The transmembrane domain, because it is made of amino acids having hydrophobic side chains, exists comfortably in the hydrophobic inner layers of the plasma membrane. Because these transmembrane domains anchor many proteins in the lipid bilayer, these proteins are not free-floating and cannot be isolated and purified biochemically without first dissolving away the lipid bilayer with detergents. (Indeed, much of the washing we do in our lives is necessitated by the need to solubilize proteins that are embedded in lipid membranes using detergents!)
Vitamins are essential aids in many body processes, converting food the energy, building and maintaining cells, and other functions.
These vitamins are fat soluble, which means they can only be absorbed with the help of fat.