Chemistry - Vitamins

Which disorder is associated with thiamin deficiency? A. Beriberi B. Pellagra C. Riskets D. Dermatitis

A. A deficiency in thiamin (vitamin B1) is associated with beriberi and Wernicke-Korsakoff syndrome. In general, thiamin deficiency affects the nervous and cardiovascular systems. Thiamin deficiency is sometimes seen in chronic alcoholics and in the elderly.

In the United States, most cases of scurvy occur in children between the ages of 7 months to 2 years. Scurvy is a disease caused by a deficiency in which of the following? A. Vitamin A B. Vitamin C C. Vitamin D D. Vitamin K

B. Ascorbic acid is commonly known as vitamin C. Because humans are unable to synthesize ascorbic acid, it is necessary that it be taken in through the diet. If ascorbic acid is not ingested in a sufficient amount, a deficiency develops that leads to the disease known as scurvy. Scurvy is characterized by bleeding gums, loose teeth and poor wound healing.

Which vitamin is a constituent of two redox coenzymes? A. Vitamin A B. Vitamin B2 C. Vitamin B6 D. Vitamin C

B. Riboflavin (vitmain B2) is a constituent of two redox coenzymes, flavin mononucleotide (FMN) and flavin-adenine dinucleotide (FAD). These coenzymes, in combination with appropriate proteins, form the flavoprotein enzymes, which participate in tissue respiration as components of the electron-transport system. The property that enables them to participate in electron-transport is their ability to exist in the half-reduced form (FADH) and in the fully reduced form (FADH2).

Which of the following techniques is more commonly used to measure vitamins? A. High-performance liquid chromatography B. Spectrophotometry C. Nephelometry D. Microbiological

A. HPLC is a commonly used technique for the measurement of vitamins. Measurement by HPLC tends to be rapid, sensitive and specific. Other techniques employed include spectrophotometric, fluorometric and microbiological assays.

Which of the following tissues is important in vitamin D metabolism? A. Skin B. Spleen C. Pancreas D. Thyroid

A. The designation "vitamin D" applies to a family of essential fat-soluble sterols that includes vitamin D3 or cholecalciferol. This compound can either be absorbed directly or synthesized in the skin from 7-dehydrocholesterol with the help of ultraviolet irradiation. For physiological functioning, vitamin D3 must be metabolized first by the liver to 25-hydroxyvitamin D3 and then by the kidney to the final hormonal product, 1,25-dihydroxyvitamin D3 (calcitriol). The kidney also synthesizes 24,25-dihydroxyvitamin D3 by an alternate pathway. This compound does not have the hormonal activity of calcitriol, but because of its similar structure and relatively high concentration in the serum, it has complicated the determination of serum calcitriol.

Which of the following is not associated with vitamin B12? A. Insoluble in water B. Intrinsic factor C. Schilling test D. Pernicious anemia

A. Vitamin B12 is a water-soluble vitamin. It is absorbed in the gastrointestinal tract by way of a substance called intrinsic factor. Deficiency of vitamin B12 produces a megaloblastic anemia. Anemia caused by a deficiency of vitamin B12 because of a lack of intrinsic factor (IF) is called pernicious anemia. The Schilling test (with and without IF) is used to diagnose pernicious anemia. It is helpful in distinguishing pernicious anemia form other malabsorption syndromes. A positive Schilling test indicates low absorption of B12 without IF and normal absorption with IF. However, in diseases of the small bowel, low absorption occurs with and without IF.

The term "lipid" encompasses a wide variety of compounds characterized as being insoluble in water but soluble in nonpolar solvents. Which of the following vitamins is not classified as fat soluble? A. Vitamin A B. Vitamin C C. Vitamin D D. Vitamin E

B. The term "lipid" encompasses a large group of compounds, including the sterols, fatty acids, triglycerides, phosphatides, bile pigments, waxes and fat-soluble vitamins. Vitamins A, D, E, and K are classified as fat-soluble vitamins. Thiamine (B1), riboflavin (B2), pyridoxine (B6), cyanocobalamin (B12), niacin, pantothenic acid, lipoic acid, folic acid, inositol, and ascorbi acid (C) are classified as water-soluble vitamins and as such are not lipid compounds.

Measuring which of the following compounds is useful in the diagnosis of steatorrhea? A. Vitamin B12 B. Vitamin C C. Carotenoids D. Folic acid

C. The definitive test for the diagnosis of steatorrhea (fat malabsorption) is the fecal fat determination that usually is done with a 72-hour collection. Carotenoids are a group of fat-soluble compounds that are precursors of vitamin A (retinol). The carotenoids are not synthesized in humans, and their absorption depends on intestinal fat absorption. Therefore, the serum carotene level is sometimes used as a simple screening test for steatorrhea. In addition to steatorrhea, other conditions, such as poor diet, liver disease adn high fever can result in below-normal carotene levels. Folic acid and vitamins C and B12 are water soluble and would not be useful for determining fat absorption.

Which of the following is another name for vitamin B12? A. Retinol B. Pyridoxine C. Cyanocobalamin D. Riboflavin

C. Vitamin B12 (cyanocobalamin) is a cobalt-containing vitamin that is necessary for normal erythropoiesis. Intrinsic factor is a gastric protein that specifically binds vitamin B12 and carries it to the ileum for absorption. The transcobalamins are a group of plasma proteins, some of which bind vitamin B12 and some of which bind both vitamin B12 and cobalamin analogs. The cobalophilins (R proteins) are those transcobalamins that can also bind the cobalamin analogs.

A deficiency in which of the following leads to increased clotting time and may result in hemorrhagic disease in infancy? A. Riboflavin B. Pyridoxine C. Tocopherols D. Menaquinone

D. Adequate amounts of vitamin K are required for the synthesis of prothrombin by the liver. Because prothrombin is an essential component of the clotting system, a deficiency of vitamin K leads to a deficiency of prothrombin, which results in a delayed clot formation. Several closely related compounds having vitamin K properties include phylloquinones, which are synthesized by bacteria. Because the intestinal flora may not be developed sufficiently in the newborn, vitamin K (menaquinone) deficiency can occur. This leads to increased clotting time, which may result in hemorrhagic disease in infancy.