Lecture 53 & 54 Flashcards
What are vitamins?
1) Vitamins are organic compounds required in the diet in small amounts
2) They are conveniently classed as fat soluble (A, D, E, & K) or water soluble (C & the B complex)
What is the recommended daily dietary allowance for Ascorbic Acid?
60 mg
What is the recommended daily dietary allowance for Niacin?
19 mg
What is the recommended daily dietary allowance for Vitamin E?
10 mg
What is the recommended daily dietary allowance for Pyridoxine?
2 mg
What is the recommended daily dietary allowance for Riboflavin?
1.7 mg
What is the recommended daily dietary allowance for Thiamine?
1.5 mg
What is the recommended daily dietary allowance for Vitamin A?
1 mg
What is the recommended daily dietary allowance for Folic acid?
400 micro g
What is the recommended daily dietary allowance for Vitamin K?
80 micro g
What is the recommended daily dietary allowance for Vitamin D?
15 micro g
What is the recommended daily dietary allowance for Vitamin B12?
3 micro g
What is the function of Vitamin A?
1) Retinol is a precursor for tinal that is used in the visual cycle and for retinoic acid that is required for maintenance of epithelial cells
2) In the visual cycle, opsin binds the 11-cis isomer of retinal. Light causes the conversion to the all-trans isomer which is only weakly bound to opsin
What occurs in Vitamin A deficiency?
1) Night blindness
2) Keratinization of epithelial cells
From what sources is Vitamin A obtained?
1) Vegetables
2) Fish liver oil
(Note: Beta-carotene is a precursor of retinol, a form of Vitamin A)
What is the RDA of Vitamin A?
1) 1000 retinol equivalents (corresponds to 1000 micro g retinol or 6000 micro g beta-carotene)
2) Excess Vitamin A is toxic
How is retinal formed?
Beta-Carotene + O2 –> 2 Retinal (Beta-Carotene dioxygenase)
How is retinoic acid converted to the all-trans form?
Retinoic acid is converted by photoisomeration
Where is retinol stored?
Retinol is stored as retinyl esters mainly in liver & adipose tissue
What is Rhodopsin?
Rhodopsin, also known as visual purple, is a biological pigment in photoreceptor cells of the retina that is responsible for the first events in the perception of light
Describe the cyclic process between 11-cis retinal & all trans retinal
11-cis retinal + Opsin –> Rhodopsin
Rhodopsin –> light + opsin + All trans retinal
What are actions in target tissues for retinol?
1) Retinol is oxidized to retinoic acid, which binds to nuclear receptors
2) Activated retinoic acid receptor stimulates responsive genes
What can retinol be obtained from?
1) Meat –> Retinol-esters –> Retinol (in lumen)
2) Retinol (in lumen) –> Retinol (in intestinal mucosal cells with help of bile acids)
3) Retinol + NAD+ –> Retinal + NADH
4) Retinal –> Retinoic acid (Oxidation)
Where can Beta-carotene be obtained from?
Vegetables –> Beta Carotene (lumen) –> Beta Carotene (intestinal mucosa with help of bile acids) + O2 –> Retinal –> Retinoic Acid
What is retinol?
1) Retinol is one of the animal forms of vitamin A
2) When converted to the retinal (retinaldehyde) form, vitamin A is essential for vision, and when converted to retinoic acid is essential for skin health, teeth remineralization and bone growth.
3) Retinol is a lipid and requires assistance in transport
4) All-trans retinoic binds to RAR receptors and 9-cis retinoic acid binds to RXR receptors
What is the function of thiamine (vitamin B1)?
Thiamine is converted to thiamine pyrophosphate which is a cofactor for oxidative decarboxylation of alpha-keto acids and for transketolase
What effect does a deficiency of thiamine (vitamin B1) have on the body?
1) Beri-beri & Wernicke-Korsakoff syndrome
2) Polyneuritis
3) Cardiac pathology
4) Edema
What are dietary sources of thiamine?
1) Beans
2) Nuts
3) Fruits
What is the recommended daily allowance of thiamine?
1.5 mg/day
What is the function of Riboflavin (vitamin B2)?
Riboflavin is a precursor for the coenzymes, FMN & FAD
What effect does a deficiency of riboflavin (vitamin B2) have on the body?
Skin lesions
What are dietary sources of riboflavin?
1) Milk
2) Liver
3) Green vegetables
What is the recommended daily allowance of riboflavin?
1.7 mg/day
Describe the formation of flavin mononucleotide (FMN) & Flavin adenine dinucleotide (FAD) from riboflavin
1) Riboflavin + ATP –> Flavin mononucleotide (FMN) + ADP
2) Flavin mononucleotide (FMN) + ATP –> PPi + Flavin adenine dinucleotide
What is the function of niacin (nicotinic acid)?
Nicotinic acid or nicotinamide are precursors for the coenzymes NAD & NADP
What effect does a deficiency of niacin have on the body?
Pellagra (dermatitis, diarrhea, dementia, and if severe, death)
What are two sources of niacin?
1) Legumes
2) Meat
What is the recommended daily allowance of niacin?
19 mg/day
What is the function of pantothenic acid?
Pantothenic acid is a precursor of pantotheine. This structure forms part of coenzyme A
What effect does a deficiency of pantothenic acid have on the body?
A deficiency is practically unknown. There may be nausea and fatigue
What are dietary sources of pantothenic acid?
Pantothenic acid is widely distributed and is synthesized by some intestinal bacteria
What is the recommended daily allowance of pantothenic acid?
An RDA has not been established, but 5-10 mg/day might be used
What is the function of pyridoxine (Vitamin B6)?
Pyridoxine (pyridoxol) is a precursor of pyridoxal phosphate (PLP) which is a coenzyme for enzymes catalyzing transamination, deamination, decarboxylation and for glycogen phosphorylase
What effect does a deficiency of pyridoxine (vitamin B6) have on the body?
1) Dermatitis
2) Convulsions
3) Microcytic anemia
What are dietary sources of pyridoxine?
1) Liver
2) Fish
3) Nuts
4) Whole grain cereals
What is the recommended daily allowance of pyridoxine?
2 mg/day
What is the function of biotin?
Biotin acts as a coenzyme in carboylation reactions in covalent linkage to lysine side chains of enzymes
What effect does a deficiency of biotin have on the body?
1) Dermatitis
2) Anorexia
3) Nausea
4) Muscle pain
What are dietary sources of biotin?
1) Intestinal microorganisms
2) Liver
3) Vegetables
What is the recommended daily allowance of biotin?
An RDA has not been established. Not avidin in raw eggs has tight binding for biotin and in high amounts can cause a biotin deficiency
What is the function of folic acid?
Folic acid is a precursor for tetrahyhdrofolate that is used as a carrier of one carbon units at different levels of oxidation
What effect does a deficiency of folic acid have on the body?
1) Megaloblastic anemia
2) GI disturbances
What are dietary sources of folic acid?
1) Intestinal bacteria
2) Liver
3) Yeast
4) Green vegetables
What is the recommended daily allowance of folic acid?
400 micrograms/day
Note: Before supplementation, folic acid deficiency was the most common vitamin deficiency in the US
What is the function of sulfanilamide?
Sulfanilamide and its derivatives competitively inhibit the synthesis of folic acid in micro organisms and, thereby, decrease the synthesis of nucleotides needed for the replication
What is the function of methotrexate?
1) Dihydrofolate reductase is competitively inhibited by methotrexate, a folic acid analogue used to effect the remission of acute leukemia in children
2) Dihydrofolate reductase normally reduces folic acid to tetrahydrofolic acid by oxidizing NADPH to NADP+
3) Tetrahydrofolic acid can then be used for Amino acid synthesis, purine synthesis, & thymidine synthesis
What is the structure vitamin B12 (Cobalamin) entail?
Vitamin B12 is a complex multiple ring structure which includes a cobalt atom
What is the function of Vitamin B12 (cobalamin)?
Derived cofactors are used for two important reactions:
1) Methylmalonyl CoA isomerase requires 5-deoxyadenosyl cobalamin
2) Homocysteine: Tetrahydrofolate methyl transferase requires methyl cobalamin
How is Vitamin 12 absorbed by the body?
Vitamin B12 is absorbed from the ileum as a complex with intrinsic factor which is produced by the gastric mucosa
What effect does a deficiency in Vitamin B12 have on the body?
1) Pernicious anemia
2) Degeneration of spinal cord neurons
What are dietary sources of Vitamin B12?
1) Meat
2) Milk
What is the RDA for Vitamin B12?
3 micrograms/day
What is the function of Vitamin C (Ascorbic acid)?
1) Ascorbic acid is a water soluble antioxidant and it promotes the hydroxylation of proline residues of collagen
2) Ascorbic acid is also required in the synthesis of carnitine, dopamine and bile acids
What effect does a deficiency of vitamin C have on the body?
Scurvy (hemorrhage, impaired wound healing, and bond formation)
What are dietary sources of vitamin C?
1) Fruits
2) Vegetables
What is the RDA for vitamin C?
60 mg/day
What is the function of vitamin D?
1) Regulation of calcium levels through actions on intestine, kidney & bone
2) Vitamin D3 (cholecalciferol) requires conversion to 1,25-dihydroxy vitamin D3 to form the active compound
What effect does a deficiency of vitamin D have on the body?
1) Rickets
2) Osteomalacia
What are dietary sources of Vitamin D?
1) UV irradiation of 7-dehydrocholesterol in the skin
2) fish liver oils
3) supplemented milk
What is the RDA for vitamin D?
600 international units (15 micrograms of cholecalciferol)
What is the function of Vitamin E (Tocopherol)?
It is a lipid-soluble antioxidant and helps to prevent lipid damage
What effect does a deficiency of vitamin E have on the body?
In humans, deficiency is associated with lysis of erythrocytes
What are dietary sources of Vitamin E?
1) Vegetables
2) Wheat germ oil
What is the RDA for Vitamin E?
15 international units. Greater amounts may be beneficial but there is conflicting data
What is the function of Vitamin K?
It is a coenzyme for the carboxylation of glutamic acid side chains of some blood clotting factors (prothrombin, factors 7, 9, & 10)
What effect does a deficiency in vitamin K have on the body?
A deficiency of vitamin K is rare, but can be associated with prolonged blood clotting times
What are dietary sources of Vitamin K?
Vitamin K is produced by intestinal bacteria
What is the RDA for vitamin K?
No RDA has been established, but 70-140 micrograms may be appropriate
What is a consequence of folic acid deficiency?
Spina bifida
