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Chapter 16 Amino Acids, Proteins, and Enzymes 16.9 Enzyme Cofactors 1 Function of Coenzymes A coenzyme prepares the active site for catalytic activity. 2 Water-Soluble Vitamins Water-soluble vitamins are • soluble in aqueous solutions. • cofactors for many enzymes. • not stored in the body. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 3 Fat-Soluble Vitamins Fat-soluble vitamins • are A, D, E, and K. • are soluble in lipids, but not in aqueous solutions. • are important in vision, bone formation, antioxidants, and blood clotting. • are stored in the body. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 4 Learning Check Identify each compound as a 1) water-soluble vitamin 2) fat-soluble vitamin. A. B. C. D. E. Folic acid Retinol (Vitamin A) Vitamin C Vitamin E Niacin 5 Solution Identify each compound as a 1) water-soluble vitamin 2) fat-soluble vitamin. A. 1 Folic acid B. 2 Retinol (Vitamin A) C. 1 Vitamin C D. 2 Vitamin E E. 1 Niacin 6 Thiamin (Vitamin B1) Thiamin • was the first B vitamin identified. • is part of the coenzyme thiamin pyrophosphate (TPP), required in the decarboxylation of -keto carboxylic acids. • deficiency results in beriberi (fatigue, weight loss, and nerve degeneration). 7 Riboflavin (Vitamin B2) Riboflavin is • made of the sugar alcohol ribitol and flavin. • part of the coenzymes flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN). • needed for good vision and healthy skin. O H3C N H3C N N N H O D-Ribitol CH2 CH CH CH CH 2 OH OH OH OH 8 Niacin (Vitamin B3) Niacin • is part of the coenzyme nicotinamide adenine dinucleotide (NAD+) involved in oxidationreduction reactions. • deficiency can result in dermatitis, muscle fatigue, and loss of appetite. • is found in meats, rice, and whole grains. O C OH N 9 Pantothenic Acid (Vitamin B5) Pantothenic acid • is part of coenzyme A needed for energy production as well as glucose and cholesterol synthesis. • deficiency can result in fatigue, retarded growth, cramps, and anemia. • is found in salmon, meat, eggs, whole grains, and vegetables. CH 3 OH O HO CH2 C CH 3 O CH C N CH 2 CH2 C OH H 10 Cobalamin (Vitamin B12) Cobalamin • consists of four pyrrole rings with a Co2+. • is a coenzyme for enzymes that transfer methyl groups and produce red blood cells. • deficiency can lead to pernicious anemia and nerve damage. 11 Ascorbic Acid (Vitamin C) Vitamin C • is required in collagen synthesis. • deficiency can lead to weakened connective tissue, slow-healing wounds, and anemia. • is found in blueberries, citrus fruits, tomatoes, broccoli, red and green vegetables. CH2OH O HO O CHOH OH 12 Folic Acid (Folate) Folic acid (folate) • consists of pyrimidine, p-aminobenzoic acid, and glutamate. • forms the coenzyme THF used in the transfer of carbon groups and the synthesis of nucleic acids. • deficiency can lead to abnormal red blood cells, anemia, and poor growth. 13 Vitamin A Vitamin A • is obtained from meats and beta-carotenes in plants. • has beta-carotenes that are converted by liver enzymes to vitamin A (retinol). H3C CH3 CH3 Beta-carotene CH3 CH3 CH3 H3C H3C CH3 CH3 CH3 CH3 H3C CH3 CH3 CH2OH Retinol (vitamin A) 14 Vitamin D Vitamin D (D3) • is synthesized in skin exposed to sunlight. • regulates the absorption of phosphorus and calcium during bone growth. • deficiency can result in weakened bones. • sources include cod liver oil, egg yolk, and enriched milk. 15 Vitamin E Vitamin E • is an antioxidant in cells. • may prevent the oxidation of unsaturated fatty acids. • is found in vegetable oils, whole grains, and vegetables. CH 3 HO CH 3 H 3C O CH 3 CH 3 CH 3 CH 3 CH 3 16 Vitamin K • Vitamin K1 in plants has a saturated side chain. • Vitamin K2 in animals has a long unsaturated side chain. • Vitamin K2 is needed for the synthesis of zymogens for blood clotting. O O CH3 CH3 CH3 CH3 3 O CH3 CH3 Vitamin K1 (phylloquinone) n O CH3 CH3 Vitamin K2 (menaquinone) 17 Learning Check Identify the vitamin associated with each 1) Thiamin (B1) 2) Vitamin A 3) Vitamin K 4) Vitamin D 5) Ascorbic Acid A. B. C. D. E. Collagen formation Beriberi Absorption of phosphorus and calcium in bone Vision Blood clotting 18 Solution Identify the vitamin associated with each 1) Thiamin (B1) 2) Vitamin A 3) Vitamin K 4) Vitamin D 5) Ascorbic Acid A. B. C. D. E. 5 1 4 2 3 Collagen formation Beriberi Absorption of phosphorus and calcium in bone Vision Blood clotting 19