Term
|
Definition
| inborn error of metabolism that affects all humans & doesnt allow us to endogenously synthesize vit. C |
|
|
Term
|
Definition
| citrus fruit, guava, red pepper, strawberries |
|
|
Term
| which stereoisomer of vit. C is the active form? |
|
Definition
|
|
Term
| what are the transporters of vit. C? |
|
Definition
| SVCT1 & SVCT2 (Na+ coupled) |
|
|
Term
| what substances/molecules affect vit. C absorption? |
|
Definition
pectin & zinc may impair absorption
excessive iron also, and copper
.. degree of vit. C absorption is inversely related to amount of intake |
|
|
Term
| where is the highest concentration(s) of vit. C in the body? |
|
Definition
| adrenal and pituitary gland .. liver has most vit. C based on total weight |
|
|
Term
| vit. C enhances the absorption of what substance? |
|
Definition
|
|
Term
| what drugs interfere with vit. C levels in the body? |
|
Definition
estrogen-containing contraceptives = lower vit. C levels in plasma & white blood cells
aspirin = increases excretion |
|
|
Term
| what disease arises from vit. C deficiency? |
|
Definition
|
|
Term
| what are risk factors for scurvy? |
|
Definition
being a pirate
babies fed only cow's milk
alcoholics & cigarette smokers (pirates)
elderly or those w/poor dietary habits
those w/limited access to fresh fruits/veggies
pregnant & lactating women
type I diabetics
Hb2 polymorphism |
|
|
Term
| what are symptoms of vit. C toxicity? |
|
Definition
abdominal pain & osmotic diarrhea (occurs when unabsorbed water-solutes remain in the bowel where they retain water)
kidney stones (one of the metabolites of vit. C is oxalate which is a main component of kidney stones)
interference of iron & copper metabolism |
|
|
Term
| what are the functions of vit. C as a cofactor? |
|
Definition
| collagen synthesis, carnitine synthesis, tyrosine catabolism, neurotransmitter synthesis, amidation of peptides, microsomal metabolism |
|
|
Term
| what are 2 functions of vit. C? |
|
Definition
| water-soluble antioxidant, pro-oxidant |
|
|
Term
|
Definition
| major structural protein present in tendons, skin, bones, cartilage, teeth, blood vessels.. |
|
|
Term
| what type of reaction does vit. C assist in for collagen synthesis? |
|
Definition
| hydroxylation of proline and lysine |
|
|
Term
| what 3 enzymes in collagen synthesis require vit. C? |
|
Definition
| prolyl 3-hydroxylase, prolyl 4-hydroxylase, lysyl-hydroxylase |
|
|
Term
| what happens to collagen synthesis with vit. C deficiency? |
|
Definition
| collagen triple helix formation is reduced |
|
|
Term
| what are the functions of carnitine? |
|
Definition
| transport of long chain fatty acids across the mito membrane, maintenance of adequate free CoA, protection of cells against toxic accumulation of acyl-CoA compounds by shuttling acyl groups out of mito, storage and transport of energy |
|
|
Term
| what two enzymes require vit. C in carnitine synthesis? |
|
Definition
| trimethyllysine hydroxylase, 4-butyrobetaine hydroxylase |
|
|
Term
| what is a consequence of reduced carnitine production due to vit. C deficiency? |
|
Definition
|
|
Term
| could vit. C deficiency cause sleep disorders? |
|
Definition
yes, involved in synthesis of serotonin, melatonin from tryptophan
scurvy pt's exp. fatigue |
|
|
Term
| vit. C is critical for function of what gland? |
|
Definition
|
|
Term
|
Definition
a molecule that is easily oxidized that prevents other molecules from being oxidized (eg. reducing agent)
antioxidants donate electrons and quench free radicals(molecule w/unpaired e-) |
|
|
Term
| how do free radicals cause damage? |
|
Definition
| attack DNA, attack enzymes and proteins (disrupt normal cell activities or membranes [if arterial epithelial cells could lead to heart attack]) |
|
|
Term
| does vit. C promote wound healing? |
|
Definition
| yes b/c of role in collagen synthesis |
|
|
Term
|
Definition
| mutation in DNA helicase - defects in DNA repair |
|
|
Term
| does vit. C impact cataract formation? |
|
Definition
| yes! high vit. C intake may reduce cataracts & age-related macular degeneration |
|
|
Term
| what are good sources of thiamin? |
|
Definition
| whole grains, meat, legumes/nuts/ green veg |
|
|
Term
| what are the forms that thiamin exists in? |
|
Definition
| free thiamin, thiamin monophosphate/pyrophosphate/triphosphate |
|
|
Term
| what are two anti-thiamin factors? |
|
Definition
thiaminases (cleaves thiamin, making it inactive)
thiamin antagonists (inactivate thiamin by oxyreductive process -> forming adducts |
|
|
Term
| how is thiamin trasported in the bloodstream? |
|
Definition
| 90% transported by RBCs, 10% is bound to albumin or as TMP |
|
|
Term
| what is the distribution of thiamin in its different forms? |
|
Definition
free thiamin is taken up by the liver & phosphorylated
TPP ~80% of total body thiamin
TTP <10%, mostly in brain & nervous system |
|
|
Term
| what does TPP (thiamin) act as a coenzyme for? |
|
Definition
| pyruvate dehydrogenase, a-ketoglutarate dehydrogenase, branched chain a-keto acid dehydrogenase, transketolase (PPP) |
|
|
Term
| why is severe metabolic acidosis caused by high levels of lactate often associated with thiamin deficiency? |
|
Definition
| thiamin is required for PDH, thus pyruvate is built up and reduced to lactate |
|
|
Term
| why does thiamin utilization increase among cancer pts? |
|
Definition
| b/c DNA replication is increased out of control, thus need for increase in nucleotides via PPP |
|
|
Term
| what happens if PDH, a-KG dehydrogenase, BCKAD are inhibited due to TPP deficiency? |
|
Definition
| accumulation of pyruvate, a-KG, BCAAs in blood which could lead to ketoacidosis |
|
|
Term
| what type of correlation exists between the need for thiamin and the amount of fat in the diet? |
|
Definition
| negative, b/c thiamin is a co-factor in the PPP more fat in diet, less need for NADPH b/c dont need to be making fat (NADPH does this) |
|
|
Term
| Symptoms of BeriBeri & deficiency of what vitamin lead to it? |
|
Definition
thiamin..
early symptoms- fatigue, irritability, poor memory, loss of appetite, sleep disturbances, abdominal discomfort & weight loss
as deficiency worsens, cardiovascular system & neurological symptoms appear |
|
|
Term
| What are three different methods to test for thiamin levels in body? |
|
Definition
1. erythrocyte transketolase activity
2. blood pyruvate, a-KG, or thiamin
3. thiamin in urine (<40ug/d) |
|
|
Term
| what are the characteristics of dry beriberi? |
|
Definition
| found predominantly in older adults as a result of chronic low thiamin intakes.. nerve and muscle abnormalities.. prickling sensation in toes, burning sensation in feet, muscle wasting, & leg cramps & pain |
|
|
Term
| what are the characteristics of wet beriberi? |
|
Definition
| heart abnormalities, heart pumps more blood & beats faster.. edema in legs/lungs which leads to decrease blood pressure & shock & death if untreated |
|
|
Term
| what are the characteristics of acute beriberi? |
|
Definition
occurs in infants (3-4wk old) who are breastfed by a mother who has a thiamin deficiency
symptoms include- anorexia, vomiting, lactic acidosis, altered HR, lack of reflexes |
|
|
Term
| Wernicke-Korsakoff syndrome |
|
Definition
thiamin deficiency associated with alcoholism .. due to decrease in food intake, liver damage & decreased thiamin absorption
causes brain abnormalities-
opthalmoplegia, nystagmus, loss of short-term memory & confusion |
|
|
Term
| What are some good sources of Riboflavin (B2)? |
|
Definition
| milk/dairy, legumes & green veggies, & grains |
|
|
Term
| is there a toxicity for riboflavin? |
|
Definition
|
|
Term
| What water soluble vitamin contributes to "intracellular cement" in the formation of scar tissue and wound healing? |
|
Definition
| vitamin C, Collagen chains are synthesized and then require a Vitamin C-dependent hydroxylation reaction to cross-link the into a triple-helix configuration. |
|
|
Term
| A primary function of Vitamin C is to act as an |
|
Definition
| antioxidant, helps to maintain copper and iron atoms in metalloenzymes |
|
|
Term
|
Definition
| Small purple or red spots on the body caused by ruptured blood vessels, these hemorrhages are one of the signs and symptoms of scurvy. |
|
|
Term
| Which classical vitamin deficiency is known for the four Ds: dermatitis, dementia, diarrhea, and death? |
|
Definition
| niacin, This vitamin was also once called the 'anti-black tongue' factor, due to the finding that black tongue in dogs and cats whose owners formulate their own food, or try to convert their pets to vegetarians. |
|
|
Term
Riboflavin deficiency results in all of the following symptoms, except:
Glossitis
Dermatitis
Cheilosis
Migraine headaches |
|
Definition
| Migraine headaches, Riboflavin has been used by some to treat migraine headaches. |
|
|
Term
| Synthesis of coenzyme A starts with the phosphorylation of which of these vitamins? |
|
Definition
| pantothenic acid, The enzyme pantohexate kinase phosphorylates pantothenic acid. |
|
|
Term
| A patient tells you they are experiencing hallucinations and a skin rash. What vitamin deficiency do you suspect is the cause? |
|
Definition
| Biotin deficiency, other symptoms would include alopecia, muscle pain and lethargy. |
|
|
Term
| A consequence of thiamin deficiency is |
|
Definition
| beriberi, it's usually associated with alcoholism in the US, most likely due to poor eating habits accompanying this condition. |
|
|
Term
| Although excess absorbed ascorbic acid is excreted in urine, the body has an estimated maximal body pool of (fill in), which can be maintained with intakes of at least 100 mg of vitamin C per day |
|
Definition
| 1500mg, The liver contains most of the vitamin C pool in the body. |
|
|
Term
| T/F: The active form of a vitamin is usually the form that has the greatest bioavailability |
|
Definition
| False, The active form usually needs to be modified from its parent form for absorption. See pages 323-324 for more information. |
|
|
Term
| Folate is made up of what components, all of which must be present for full activity of this vitamin. |
|
Definition
| Glutamic Acid, Pteridine, and Para-aminobenzoic acid .. In the body, folate has multiple glutamic acid residue attached when metabolically active. |
|
|
Term
Which of the following water-soluble vitamins is found so widely distributed in all plant and animal foods that deficiencies are unlikely?
Riboflavin
Folic Acid
Panthothenic Acid
Vitamin B1 |
|
Definition
| Panthothenic Acid, This is easy to remember, if you know that the Greek word "pantos" means "everywhere" |
|
|
Term
Which of the following vitamins has an established "Tolerable Upper Intake Level", and why?
Niacin
Riboflavin
Vit B6
Vit B12 |
|
Definition
| Vitamin B6, due to possible sensory neuropathy, The upper limit is 100 mg/day for adults. |
|
|
Term
| A good source for Vitamin B6 is muscle meats because PLP is predominantly bound to which enzyme? |
|
Definition
| Glycogen Phosphorylase, Pyridoxal phosphate (PLP) are high in sirloin steaks, salmon and chicken breast. |
|
|
Term
| True/False: Biotin and Vitamin B12 are both required for the synthesis of odd-chain fatty acids. |
|
Definition
| False, They are both required for the oxidation, not the synthesis of odd chain fatty acids. |
|
|
Term
| Which three vitamins are involved in the synthesis of fatty acids? |
|
Definition
| Niacin, biotin, and pantothenic acid, |
|
|
Term
| Water-soluble vitamins are not stored, but readily excreted--with the one exception to this being the storage of folate by the liver. |
|
Definition
| False, It is not folate, but vitamin B12 which can be stored by the liver. |
|
|
Term
| Which of the following would you find under B12-deficient conditions and the methyl trap hypothesis? |
|
Definition
| accumulation of 5-methyl THF, This is because there is a synergistic relationship between vitamin B12 and folate, in which without vitamin B12, the methyl group from 5-methyl THF can't be removed, and is "trapped" |
|
|
Term
| Folate is vitally important for dividing cells during growth and cancer because of its essential role in the synthesis of _____. |
|
Definition
|
|
Term
| what coenzyme/vitamin is needed for ACC? |
|
Definition
|
|
Term
| what coenzyme is needed for aldehyde dehydrogenase? |
|
Definition
|
|
Term
| what coenzyme is needed for glutathione reductase? |
|
Definition
| flavin adenine dinucleotide |
|
|
Term
| what coenzyme is needed for pyruvate dehydrogenase? |
|
Definition
|
|
Term
| what coenzmye is required for alanine aminotransferase? |
|
Definition
|
|
Term
| Niacin (B3) was discovered through which condition? |
|
Definition
| pellagra, prevalent in regions where corn is a staple |
|
|
Term
| what are good sources of niacin? |
|
Definition
| fish, meat, enriched grains, coffe & tea, supps |
|
|
Term
|
Definition
| deficiency of niacin; affects skin, digestive tract, and brain.. develops if tryptophan is also deficient.. |
|
|
Term
| what are the symptoms of pellagra? |
|
Definition
| the 4 D's: Dermatitis, Dementia, Diarrhea & Death |
|
|
Term
| what are the two terms for the niacin derivatives? |
|
Definition
| Nicotinic acid and nicotinamide |
|
|
Term
| what derivative of niacin is used to form NAD, NADP? |
|
Definition
|
|
Term
| what are the characteristics of Hartup disease and what vitamin is it associated with? |
|
Definition
| Niacin.. its an autosomal recessive disorder, affects AA transport in intestine/kidneys, SLC6A19 is Na+ dependent AA transporter, poor nutrition precedes onset of disease, pellagra-like sympoms |
|
|
Term
| When nicotinamide enters cells what is it converted to? |
|
Definition
| NAD then phosphorylated to make NADP.. [NAD] > [NADP] in the cell.. NAD+ and NADPH are the predominant forms |
|
|
Term
| where does the metabolism of niacin take place? |
|
Definition
| liver with conversion of N-methyl nicotinamide .. & excretion by the kidneys |
|
|
Term
| what type of reactions is Niacin involved in? |
|
Definition
oxidative rxns (glycolysis, TCA, B-oxidation, EtOH)
catabolic rxns (catabolism of B6)
non-redox (ribosylation)
reductive biosynthesis (FAS, chol hormone synthesis, DNA precursors, regeneration of vit. C)
Folate metabolism |
|
|
Term
| as it relates to niacin, what is the consequence of a diet poor in this vitamin/alcoholism? |
|
Definition
| slower metabolism of EtOH b/c NAD/NADPH involved in alcohol dehydrogenase pathway & microsomal ethanol system |
|
|
Term
| what are good sources of pantothenic acid (B5)? |
|
Definition
| all plant and animal foods, lost in highly processed foods |
|
|
Term
| Is there a deficiency with Pantothenic acid and what are the symptoms if so? |
|
Definition
yes, but rare. has been reported with severe malnutrition
symptoms include: vomiting, fatigue, weakness, irritability |
|
|
Term
| what conditions may increase the need for pantothenic acid? |
|
Definition
| alcoholism, diabetes mellitus, and inflammatory bowel disease .. |
|
|
Term
| where is pantothenic acid principally absorbed? |
|
Definition
jejunum.. passive diffusion at high conc. Na+-dependent SMVT at low concentrations .. which is used by the heart, muscle, brain, kidney & liver cells
biotin also uses the SMVT transporter |
|
|
Term
| where is pantothenic acid stored? |
|
Definition
| in all mitochondria containing cells.. small amounts are stored in RBCs and adipose tissue.. mostly used to resynthesize CoA |
|
|
Term
| what are the functions of the pantothenic derivative CoA? |
|
Definition
| fatty acid synthesis, fat/carb/AA oxidation, ketone metabolism |
|
|
Term
| what form of pantothenic acid links directly to form Acyl Carrier Protein (ACP)? |
|
Definition
| 4'-phosphopentetheine, ACP is needed for FAS |
|
|
Term
| does redundancy of a gene (ex. 4 PANK genes in humans) equate to importance of the process? |
|
Definition
| yes, not clear however.. ex, PANK gene encodes enzyme in 1st step of CoA synthesis from Pantothenic Acid.. if faulty, death by early adulthood |
|
|
Term
| folic acid is the ___ form of vitamin B9 |
|
Definition
|
|
Term
| folate is the ____ form of vitamin B9 |
|
Definition
|
|
Term
| what are good sources of folate? |
|
Definition
| mushrooms, green veg, legumes, fruits, and liver.. higher in raw foods, where it is primarily found as 7,8 dihydrofolate polyglutamates |
|
|
Term
| lack of folate fortification is associated with what kind of defects? |
|
Definition
|
|
Term
| processing, food prep and cooking results in an increase or decrease of the bioavailability of folate? |
|
Definition
|
|
Term
| what are the different assessments for folate levels in the body? |
|
Definition
plasma, serum or RBC folate levels
FIGLU (N-formiminoglutamate) urinary excretion
-formed during catabolism of histidine, needs THF to break down
-given oral histidine & measure FIGLU excretion in urine
**folate deficiency = increased FIGLU excretion |
|
|
Term
| what is a functional marker of folate and B12 deficiencies? |
|
Definition
| plasma homocysteine concentration |
|
|
Term
| what form must folate be in to be absorbed? (polyglutamate or monoglutamate) |
|
Definition
| polyglutamate must be hydrolyzed to monoglutamate |
|
|
Term
| how does chronic alcohol intake affect folate digestion? |
|
Definition
| it impairs the hydrolase activity leading to decreased digestion of polyglutamate to mono.. thus decreased folate absorption |
|
|
Term
| Where does folate absorption occur? |
|
Definition
| jejunum, active Na+ dependent at low concentrations, passive at high conc. |
|
|
Term
| what are the 5 inborn genetic errors associated with folate? |
|
Definition
hereditary folate malabsorption
glutamate formiminotransferase deficiency (FTCD gene)
methylenetetrahydrofolate reductase deficiency (MTHFR gene)
functional methionine synthase deficiency (MTR/MTRR gene) |
|
|
Term
| what should be a dietary recommendation for a female carrier of the TT genotype for the MTHFR gene who is trying to conceive? |
|
Definition
| she should take double the folate supp's of the CC genotype |
|
|
Term
| list the THF derivatives from most oxidized to most reduced 1-5 |
|
Definition
1. 5- and 10-formyl THF
2. 5-forminino THF
3. 5,10-methenyl THF
4. 5,10-methylene THF
5. 5-methyl THF |
|
|
Term
| what are the main storage forms of folate in the body? |
|
Definition
| polyglutamate THF & 5-methyl THF |
|
|
Term
| what part of the cell is folate found in? |
|
Definition
| mitochondria and cytoplasm |
|
|
Term
| what are the coenzyme functions of folate? |
|
Definition
1-carbon metabolism
AA metabolism (histidine catabolism, interconversion of Serine & Glycine, Methionine regeneration from homocysteine
purine & pyrimidine synthesis (important in DNA & RNA synthesis) |
|
|
Term
| is the conversion of Gly to Ser ir/reversible? |
|
Definition
| it is reversible and uses THF & PLP (B6) |
|
|
Term
| what vitamin does glycine degradation require? |
|
Definition
|
|
Term
| where does the synthesis of glycine from choline occur and what vitamins are needed? |
|
Definition
| occurs in the mitochondria of liver & kidney cells & requires folate & niacin |
|
|
Term
| what is a metabolic consequence of trapping folate at methyltetrahydrofolate? |
|
Definition
| reduced folate availability, megablastic anemia, reduced methionine |
|
|
Term
| what two enzymes are active during cell division? |
|
Definition
| thymidylate synthase (TS) and dihydrofolate reductase (DHFR) |
|
|
Term
| what form of THF is needed for purine (A & G) ring formation? |
|
Definition
|
|
Term
| what are the symptoms of folate deficiency? |
|
Definition
| anemia, fatigue, paleness, irritability, shortness of breath.. a severe deficiency may result in depression, dementia, peripheral neuropathy, megaloblastic anemia, hyperhomocysteinemia |
|
|
Term
| What is folate deficiency associated with? |
|
Definition
| increased cancer risk(esp colon) & neural tube defects.. folate is needed for DNA synthesis & repair |
|
|
Term
| what population groups are at risk of folate deficiency? |
|
Definition
| chronic alcohol abusers, elderly, pregnant women, people with anticonvulsant meds |
|
|
Term
| how does methotrexate work as a cancer treatment? |
|
Definition
| it competes with DHFR which inhibits the conversion of DHF to THF which is required for the synthesis of DNA.. thus stopping cancer proliferation |
|
|
Term
| is there a toxicity of folate? |
|
Definition
| yes, but rare.. sypmtoms include insomnia, irritability, GI distress |
|
|
Term
| what is the primary active form of folate? |
|
Definition
|
|
Term
| what 3 roles does folate play in the body? |
|
Definition
| AA metabolism, hematopoiesis, and DNA synthesis |
|
|
Term
| what population has a critical need for folate? |
|
Definition
|
|
Term
| what type of deficiency can folate supplementation mask? |
|
Definition
|
|
Term
| what are good sources of Biotin (B7)? |
|
Definition
| egg yolks, liver, soybeans, yeast |
|
|
Term
| what glycoprotein irreversibly binds to biotin and prevents its absorption? |
|
Definition
| avidin, which is heat liable |
|
|
Term
| what types of research procedures use tthe avidin-biotin interaction? |
|
Definition
| western blots, immunohistochemistry, immunoprecipitation |
|
|
Term
| define a biotinidase deficiency. |
|
Definition
| autosomal recessive genetic disorder of metabolism, neurocutaneous disorder.. can use a molecule of biotin only once-biotin cannot be recycled.. results in seizures, ataxia, skin rash, hair loss |
|
|
Term
| how would you differentiate between a genetic or a nutritional biotin deficiency? |
|
Definition
| use biotin supps, then sequence their genome |
|
|
Term
| where is biotin absorbed and what transporter is utilized? |
|
Definition
| jejunum and ileum (where SMVT is used) .. passive diffusion at high conc. Na+ dependent at low doses |
|
|
Term
| what can inhibit biotin absorption? |
|
Definition
|
|
Term
|
Definition
| excreted in the urine. absorbed biocytin not metabolized by biotinidase is excreted in the urine.. unabsorbed biotin & biotin produced by intestinal bacteria not absorbed excreted in feces |
|
|
Term
| what are the two main functions of biotin? |
|
Definition
coenzyme for carboxylases
non-coenzyme in gene expression & cell signaling |
|
|
Term
| what four key carboxylases is biotin a coenzyme for? |
|
Definition
| pyruvate carboxylase, ACC, propionyl CoA carboxylase, B-methylcrotonyl CoA carboxylase |
|
|
Term
| what roles does histone biotinylate (noncoenzyme of biotin) play? |
|
Definition
| cell proliferation, gene silencing, DNA repair .. |
|
|
Term
| in what circumstances does biotinylation of histones appear to increase? |
|
Definition
| in response to cell proliferation and in response to DNA damage |
|
|
Term
| what are deficiencies for biotin? |
|
Definition
|
|
Term
| is there a toxicity for biotin? |
|
Definition
|
|
Term
| is biotin found in animal, plant, or both sources? |
|
Definition
|
|
Term
| does biotin have conenzyme, noncoenzyme function or both? |
|
Definition
|
|
Term
| what are 3 functions of cobalamin (vit B12)? |
|
Definition
| RBC formation, neurological function, and DNA synthesis |
|
|
Term
| what are the primary sources of B12? |
|
Definition
| animal products ex. meat, poultry, fish, shellfish, eggs.. plants dont have B12 |
|
|
Term
| what populations would you expect to have lower levels of B12? |
|
Definition
|
|
Term
| what are the two pathways of vit B12 absorption? |
|
Definition
intrinsic factor and R proteins
passive diffusion |
|
|
Term
| what is cobalamin usually bound to when ingested? |
|
Definition
|
|
Term
| what causes impaired absorption of B12? |
|
Definition
| gastric atrophy, achlohydria (lack of HCl in stomach), inadequate protein digestion, lack of Intrinsic Factor (IF) production, loss of IF-B12 receptors in the ileum, and parasitic infections |
|
|
Term
| what are causes of gastric atrophy, achlohydria |
|
Definition
-less pepsin activated -> less B12 released from food proteins
-chronic antacid use
-zollinger-ellison syndrome (increase gastrin -> excess HCl production) |
|
|
Term
| what causes inadequate protein digestion? |
|
Definition
| pancreatic insufficiency, which is a major cause of B12 deficiency since pancreatic proteases are needed to release B12 from R-protein |
|
|
Term
| what decreases IF production? |
|
Definition
destruction of parietal cells, due to aging
also autoimmune condition that antibodies attack gastric parietal cells and reduced IF production - causes pernicious anemia |
|
|
Term
| what causes a loss of IF-B12 receptors in the ileum? |
|
Definition
| removal of ileum or inflammation |
|
|
Term
| is reabsorption of B12 thru the enterohepatic circulation (EC) dependent on IF? |
|
Definition
|
|
Term
| how is vit B12 reabsorbed? |
|
Definition
| enterohepatic circulation.. liver -> gall bladder -> small intestine & absorbed again |
|
|
Term
| what is the main form of cobalamin in the blood? |
|
Definition
| 60-80% methylcobalamin & 20% adenosylcobalamin .. usually bound to R-proteins |
|
|
Term
| does B12 have a long or short storage time? |
|
Definition
|
|
Term
| where in the body is B12 primarily stored? |
|
Definition
| liver.. some in muscle, bone, kidneys, heart, brain, and spleen |
|
|
Term
| how is most of the B12-R complex excreted? |
|
Definition
in the bile (feces) if unabsorbed bile B12, sloughed intestinal cells & secretions, B12 from intestinal bacteria
if excess B12 in blood, then excreted in urine |
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Term
| what are the two coenzyme forms of cobalamin in humans? |
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Definition
| methylcobalamin, adenosylcobalamin |
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Term
| Resynthesis of _____ from ___ is dependent on folate and B12 |
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Definition
| methionine from homocysteine |
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Term
| what enzyme is required for regeneration of methionine from homocysteine? |
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Definition
| methionine synthase, which uses B12 |
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Term
| what types of reactions/stuff is B12 needed for? |
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Definition
| DNA synthesis, oxidation of odd-chain fa's, RBC formation |
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Term
| what enzyme requires B12 in the transformation of L-methylmalonyl CoA to succinyl CoA? |
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Definition
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Term
| what age group should have a B12 supp? |
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Definition
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Term
| how is B12 status assessed? |
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Definition
| Blood/Serum tests.. insufficient vit B12 leads to decrease in enzyme actvity and increase in methylmalonyl CoA, methylmalonic acid, & homocysteine |
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Term
| what is the Schilling test? |
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Definition
| determines whether the problem with low blood B12 is related to IF insufficiency by administering tracer-labeled Vit B12 and measure urinary excretion over various times (clinically diagnoses pernicious anemia |
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Term
| what is a vit B12 deficiency? |
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Definition
| megaloblastic anemia.. decreased plasma B12, decreased DNA synthesis, increased homocysteine and methylmalonic acid in serum, which leads to the meg. anemia |
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Term
| what is pernicious anemia and what vit. is it associated with? |
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Definition
| B12, its a form of megaloblastic anemia, caused by atrophic gastritis & parietal cell loss.. autoimmune condition in which antibodies attack gastric parietal cells reducing IF production and impairing B12 absorption |
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Term
| what are the main disease states related to B12 deficiency? |
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Definition
| megaloblastic anemia, pernicious anemia, hyperhomocysteinemia, inadequate absorption |
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Term
| who is at risk of inadequate B12 absorption? |
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Definition
| elderly, alcoholics, vegan vegans, people w/o stomach or ileum.. can be corrected with supp |
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Term
when comparing folate and B12 deficiency elevated/normal levels of what 2 compounds indicate a deficiency of..
1. B12
2. Folate |
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Definition
1. B12 = elevated methylmalonate and homocysteine
2. folate = normal methylmalonate and elevated homocysteine |
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Term
| absorption of B12 requires which organs to be functional? |
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Definition
| stomach, pancreas, and ileum |
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Term
| what pathway conserves B12? |
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Definition
| enterohepatic circulation |
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Term
| what are good sources vitamin B6? |
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Definition
| whole grains, starchy veg, bananas, nuts fortified cereals, meat, fish poultry.. can be lost thru processing |
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Term
| what must happen to vit B6 vitamers to be absorbed? |
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Definition
| they must be dephosphorylated to PN, PL, or PM |
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Term
| what is the difference between the vit. B6 vitamers PL/PM and PN absorption? |
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Definition
PL & PM are absorbed primarily in jejunum via passive diffusion
PN is absorbed by Na+-dependent carrier system |
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Term
| what are PL, PN, and PM converted to when they enter the liver? |
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Definition
| PLP which is the main form found in systemic blood.. bound to albumin in plasma .. PL, PN & PM can be taken up by RBCs, converted to PLP & bound to Hgb |
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Term
| what is the main organ that takes up and metabolizes B6? |
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Definition
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Term
| what must happen to PLP before it can be taken up by tissue? |
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Definition
| hydrolyzed by alkaline phosphatase |
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Term
| how is B6 (PL) trapped in the cell? |
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Definition
| phosphorylated by pyridoxal kinase to PLP |
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Term
| where is most body PLP found? |
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Definition
| ~75% in skeletal muscle bound to glycogen phosphorylase |
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Term
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Definition
| mostly thru urine by being oxidized to 4-pyridoxic acid in liver, little thru feces |
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Term
| what are the major forms of B6 in the blood? |
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Definition
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Term
| what forms of B6 can enter cells? |
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Definition
| PL, PN, PM.. PLP must be dephosphorylated |
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Term
| what kinase phosphorylates PL, PN and PM in the cell? |
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Definition
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Term
| when does PLP remains phosphorylated? |
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Definition
| when it is bound to protein |
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Term
| what happens to excess PL in the cell? |
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Definition
| it is oxidized to pyridoxic acid and excreted in urine |
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Term
| what are some of the different types of reactions that involve PLP? |
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Definition
| transaminations, decarboxylations, transulfhydrations/desulfhydrations, dehydration/deamination, cleavage, racemizations .. also involved in various synthesis rxns |
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Term
| what is an example of a transamination rxn that PLP may be used in? |
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Definition
1. corresponding a-KA of the AA is produced along with PMP
2. transamination is completed as a new a-KA substrate receives the amino group from the PMP generating the corresponding AA, along with regeneration of PLP |
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Term
| how is PLP used in a decarboxylation reaction? |
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Definition
| removal of carboxy group from a compound.. PLP is a coenzyme for glutamate decarboxylase in rxn of glutamate to GABA |
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Term
| How is PLP used in transulfhydration? |
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Definition
| PLP is required as coenzyme for rxns transforming cysteine from methionine |
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Term
| how is PLP involved in dehydration or elimination rxns? |
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Definition
| PLP-dependent threonine dehydratase removes water & NH2 from threonine, for ex |
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Term
| how is PLP used in cleavage? |
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Definition
| PLP is coenzyme for a transferase that transfers the hydroxymethyl group of Ser to THF generating glycine |
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Term
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Definition
| interconversion of D & L-amino acids |
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Term
| ___ is required for the synthesis of heme |
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Definition
| PLP.. vit B6 also helps increase the amount of O2 carried by Hgb |
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Term
| __ is required for the synthesis of NAD |
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Definition
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Term
| __ is involved in the synthesis of carnitine |
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Definition
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Term
| how is PLP used in glycogen degradation? |
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Definition
| glycogen is catabolized by PLP-dependent glycogen phosphorylase in the liver and muscle to form G1P |
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Term
| how is vit. B6 assessed for nutritional status? |
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Definition
| plasma PLP, xanthurenic acid excretion following a Trp load test, urinary B6 & 4-pyridoxic acid |
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Term
| ___ has a role in threonine DH, glycogen phosphorylase, formation of NAD, conversion of methionine to cysteine |
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Definition
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Term
| What are the symptoms of B6 deficiency? |
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Definition
| rare, but sleepiness, fatigue, cheilosis, glossitis, stomatitis, neurological problems, low thyroid hormone levels |
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Term
| what happens with hyperhomocysteinemia? |
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Definition
| insufficient PLP accumulates homocysteine which leads to decreased cystathione and cysteine |
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Term
| who is at risk for a B6 deficiency? |
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Definition
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Term
| what are the symptoms of B6 toxicity? |
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Definition
| unsteady gait, neuropathy (due to loss of myelination & sensory fibers in nerves) .. doses of vit B6 have been used to treat several conditions including hyperhomocysteinemia, carpal tunnel syndrome, premenstrual syndrome, muscular fatigue, numbness.. but controversial |
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Term
| what is the active form of vit B6? |
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Definition
| PLP.. required coenzyme for many rxns, particularly AA metabolism |
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Term
| how many vitamers does B6 have? |
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Definition
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