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Biochemistry > Water Soluble Vitamins > Flashcards

Water Soluble Vitamins Flashcards

1
Q

Thiamin characteristics

A

. 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

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2
Q

Thiamin functions

A

. 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

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3
Q

Thiamin Hypovitaminosis

A

. Rare

. When severe (only rice diet) causes advanced neuromuscular symptoms, atrophy, and weakness of mm., edema, and HF

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4
Q

Moderately severe thiamine deficiency

A

. Mental confusion
. Ataxia
. Ophthalmoplegia (loss of eye coordination)
. Common in chronic alcoholics (Wernicke’s-Korsakoff syndrome)

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5
Q

Less severe thiamin deficiency

A

. More common in elderly
. Earliest symptoms: loss of appetite, constipation, nausea, mental depression, peripheral neuropathy, irritability, and fatigue

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6
Q

Riboflavin characteristics

A

. B2
. Metabolized to coenzymes FAD and FMN
. Sources: milk, eggs, liver, green leafy vegetables, fortified food
. Decomposes when exposed to visible light

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7
Q

Riboflavin function

A

Redox for 70 enzymes

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8
Q

Riboflavin hypovitaminosis

A

. Rare, but alcoholics can be deficient

. Causes angular cheilitis, glossitis, and scaly dermatitis

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9
Q

Niacin (nicotinic acid) characteristics

A

. 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

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10
Q

Niacin hypovitaminosis

A

.severe: pellagra
. Dermatitis, diarrhea, dementia
. Rare in developing world but alcoholics can develop it

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11
Q

Niacin moderate deficiency

A

. Lethargy
. Irritability
. Nervousness
. Depression

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12
Q

Pyridoxine characteristics

A

. Metabolized to coenzyme pyridoxal phosphate
. Sources: meats, grains
. B6

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13
Q

Pyridoxine functions

A

. 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

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14
Q

Pyridoxine hypovitaminosis

A

. 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

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15
Q

Pantothenic acid

A

. Metabolized to CoA and phosphopanotheine (prosthetic group of FA synthase)
. Function: CoA or acyl transfers in over 70 enzymes
. Sources: liver, egg, milk

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16
Q

Panothenic acid hypovitaminosis

A

. Rare bc it is abundant in most foods

. No recognized disease

17
Q

Biotin

A

. 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

18
Q

Biotin hypovitaminosis

A

. 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

19
Q

Vitamin B12

A

. 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

20
Q

Absorption of B12

A

. 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

21
Q

B12 in pancreatic disease

A

. Less cobalamin available to bind IF w/ loss of absorptive capacity for this vitamin

22
Q

Activation and function of B12

A

. W/in cells B12 is converted to 2 active forms

. Only 2 metabolic pathways in the body require cobalamin coenzymes

23
Q

Hypovitaminosis of B12

A

. 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

24
Q

Methyl malonyl coa

A

, competitive inhibitor of malonyl CoA in FA biosynthesis

. Causes eventual destruction of the myelin sheath

25
Q

Pernicious anemia

A

. Deficiency or inability to utilize B12

. Most common cause: lack of intrinsic factor from autoimmune rxn that destroys parietal cells

26
Q

T/F plans do not contain B12

A

T

27
Q

Folic acid absorption

A

. 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

28
Q

Folic acid function

A

. Tetrahydrofolate acts as 1C transfer agent

29
Q

Methyl—folate trap hypothesis

A

. 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

30
Q

Folic acid hypovitaminosis

A

. Results in anemia of macrocytic type

31
Q

Sources of folic acid

A 
. Green leafy vegetables 
. Liver
. Whole grain cereals
. Nuts
. Legumes
. Orange juice 
. It is easiest to become deficient, alcoholics frequently deficient
32
Q

Ascorbic acid

A

. 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

33
Q

Ascorbic acid hypovitaminosis

A

. 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

Biochemistry (64 decks)

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