Water Soluble Vitamins Flashcards
Thiamin characteristics
. Vit B1
. Absorbed in small intestine
. Metabolized to coenzyme thiamin pyrophosphate by thiamine pyrophosphokinase 1
. Expression highest in liver and brain
. Sources: meats, grains, legumes, fortified foods
Thiamin functions
. Role in TCA cycle and other glucose metabolism
. Necessary coenzyme for 3 critical dehydrogenase and other enzymes (pyruvate dehydrogenase, alpha-ketogenic-glutarate dehydrogenase, branched chain keto acid dehydrogenase, transketolase)
, transmission of n. Impulses
Thiamin Hypovitaminosis
. Rare
. When severe (only rice diet) causes advanced neuromuscular symptoms, atrophy, and weakness of mm., edema, and HF
Moderately severe thiamine deficiency
. Mental confusion
. Ataxia
. Ophthalmoplegia (loss of eye coordination)
. Common in chronic alcoholics (Wernicke’s-Korsakoff syndrome)
Less severe thiamin deficiency
. More common in elderly
. Earliest symptoms: loss of appetite, constipation, nausea, mental depression, peripheral neuropathy, irritability, and fatigue
Riboflavin characteristics
. B2
. Metabolized to coenzymes FAD and FMN
. Sources: milk, eggs, liver, green leafy vegetables, fortified food
. Decomposes when exposed to visible light
Riboflavin function
Redox for 70 enzymes
Riboflavin hypovitaminosis
. Rare, but alcoholics can be deficient
. Causes angular cheilitis, glossitis, and scaly dermatitis
Niacin (nicotinic acid) characteristics
. B3
. Humans can synthesize small amount from Trp
. Metabolized to coenzymes NAD/NADP
. Function: redox for 50 enzymes , pharmacological doses(2-4gm/day) produce vasodilation, dec. mobilization of FAs from adipose, dec. levels of cholesterol and lipoproteins (esp. LDL), attenuate hyperlipidemias
. Sources: meats, grains, fortified foods
Niacin hypovitaminosis
.severe: pellagra
. Dermatitis, diarrhea, dementia
. Rare in developing world but alcoholics can develop it
Niacin moderate deficiency
. Lethargy
. Irritability
. Nervousness
. Depression
Pyridoxine characteristics
. Metabolized to coenzyme pyridoxal phosphate
. Sources: meats, grains
. B6
Pyridoxine functions
. Coenzyme in pathways hat catalyze transaminations, deaminaions, decarboxylations, condensations
. Involve AA and glycogen catabolism, neurometabolism, myelin and sphingolipid biosynthesis, heme biosynthesis, and conversion of Trp to niacin
Pyridoxine hypovitaminosis
. Severe: peripheral neuropathy, sideroblastic anemia in presence of adequate Fe
. Early deficiency symptoms: lethargy, irritability, nervousness and depression
. Women taking oral contraception should double RDA
Pantothenic acid
. Metabolized to CoA and phosphopanotheine (prosthetic group of FA synthase)
. Function: CoA or acyl transfers in over 70 enzymes
. Sources: liver, egg, milk
Panothenic acid hypovitaminosis
. Rare bc it is abundant in most foods
. No recognized disease
Biotin
. Linked to amino group of Lys in apoenzyme but can exist free
. Digestion of dietary protein w/ linked biotin initially yields biotinyl lysine (biocytin) that has to be hydrolyzed to yield free biotin
. Function: carboxylation rxns
Biotin hypovitaminosis
. Rare
. Symptoms: dermatitis, anorexia, mm. Pain. Glossitis, nausea, hyperesthia (obnormal sensitivty of skin)
. Deficiency cause: eating over 20 raw egg whites/day bc the protein avidin binds biotin and it can’ be absorbed by intestine
. Intestinal flora produces half of daily supply
Vitamin B12
. 2 active forms: adenosyl cobalamin and methyl cobalamin, 5’-deoxyadenosyl group replaced w/ methyl group
. Ingested version: hydroxy-cobalamin, OTC talent version: cyano-cobalamin, both need to be metabolized to active forms
. Sources: organ meats, oysters, cheddar cheese
Absorption of B12
. Requires intrinsic factor (synthesized/secreted by parietal cells)
. R-proteins bing cobalamin and are secreted by salivary glands and stomach
. When acidic: R-proteins bind cobalamin more strongly than IF and are degraded by pancreatic proteinases
. In ileum, IF binds to ideal receptor the cross the ideal mucosa where IF is released and B12 is transferred to plasma transport proteins
B12 in pancreatic disease
. Less cobalamin available to bind IF w/ loss of absorptive capacity for this vitamin
Activation and function of B12
. W/in cells B12 is converted to 2 active forms
. Only 2 metabolic pathways in the body require cobalamin coenzymes
Hypovitaminosis of B12
. Deficiency won’t happen for years bc liver holds enough for 6-12 yrs
. Deficiency causes neurologic damage from progressive demyelination of nerve cells from inc. methyl Malonyl CoA
Methyl malonyl coa
, competitive inhibitor of malonyl CoA in FA biosynthesis
. Causes eventual destruction of the myelin sheath
Pernicious anemia
. Deficiency or inability to utilize B12
. Most common cause: lack of intrinsic factor from autoimmune rxn that destroys parietal cells
T/F plans do not contain B12
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Folic acid absorption
. Has up to 7 glutamic acid residues attached to each other via peptide bonds btw gamma-carboxylase of 1 residue and amino group of another
. Humans absorb monoglutamate form, all other hydrolyzed by enzyme conjugase at brush border
. Mono form transferred to tissues where it is again polyglutamated by another intracellular enzyme system and is active then
. Reduced to tetrahydro form before it can be a carrier of 1C units
Folic acid function
. Tetrahydrofolate acts as 1C transfer agent
Methyl—folate trap hypothesis
. If rxn From homocysteine to met. Is blocked by B12 deficiency, then N5-methyl-FH4 accumulates causing functional deficiency of FH4
. Interferes w/ nuclei acid biosynthesis
Folic acid hypovitaminosis
. Results in anemia of macrocytic type
Sources of folic acid
. Green leafy vegetables . Liver . Whole grain cereals . Nuts . Legumes . Orange juice . It is easiest to become deficient, alcoholics frequently deficient
Ascorbic acid
. Vit. C
. Active in form that its ingested
. Functions: hydroxylation of prolyl and lysyl residues in collagen, promote non-heme iron absorption in intestine, water-soluble antioxidant in aq. Compartments, may prevent senile cataracts
. Sources: citrus fruits, tomatoes, potatoes, green veggies
Ascorbic acid hypovitaminosis
. Scurvy (sore gums, loose teeth, fragile vessels, swollen joints, dec. wound healing, hemorrhaging. Anemia) from impaired collagen production
. Smoking, oral contraceptives and corticosteroids lower serum levels so you need more
. Stress may also require higher RDA
