Vitamin B1-B3

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  1. 1. Very basically, what is the function of vitamin B1? (2)
    1.5 What are thiamin's specific functions? (3 main ones, 1-3, 2-1, 3-1)
    2. What are sources of B1?
    3. What are the vitamins and minerals added to enriched grains and products? (4, 1)
    • 1. Coenzyme in carb and BCAA metabolism
    • 1.5.
    • (1) A-keto acid dehydrogenases: PDH, a-ketoglutarate dehydrogenase (TCA), and BC a-keto acid DH
    • (2) transketolase (PPP and hexose monophosphate pathway) - formation of ribose.
    • (3) Biosynthesis of NTs.

    • 2. Enriched/fortified/whole-grain products
    • 3. B1, B2, B3, B9 and Fe
  2. 1. Where are vitamins in rice found?
    2. If someone's staple is polished rice, what might they be deficient in?
    3. What if someone's staple is corn? Why?
    • 1. Found in aleurone cell layer (polished rice is only the endosperm)
    • 2. B1 and B3
    • 3. B3, because corn contains a protein that tightly binds to niacin, vastly reducing its bioavailability.
  3. 1. What are the four forms of thiamin?
    2. Which is the active form?
    3. What is the IC form?
    4. What form can be found in EC?
    5. What is the predominant form?
    • 1. Thiamin mono/di/triphosphate and free thiamin.
    • 2. Thiamin pyrophosphate (TPP) aka thiamin diphosphate
    • 3. Thiamin monophosphate
    • 4. Free thiamin
    • 5. TPP
  4. Absorption of thiamin
    1. Transporters (2)
    2. Type of transport? (i.e., active, etc)
    3. What happens if you lose one or the other?
    4. Where else are these transporters found (3)
    5. What happens when someone consumes excess?
    • 1.THTR1 and THTR2 (Thiamin transporters 1 and 2)
    • 2. Active
    • 3. THTR1 doesn't matter, but THTR2 loss leads to impairment of intestinal uptake --> decreases B1 levels in blood.
    • 4. Many tissues, esp brain kidney heart
    • 5. Absorption declines rapidly
  5. 1. How is B1 transported in blood? (2)
    2. What transporters are used to uptake B1 into cells?
    3. What is IC form of B1? How is it usually found?
    4. How is B1 stored? (5)
    • 1. 90% bound to RBCs; albumin
    • 2. THTR1 and 2.
    • 3. P'lated form - bound to proteins.
    • 4. Essentially no storage - 25-30 mg stored mostly in kidney, liver, brain, heart, and skeletal muscle
  6. 1. Where are thiamin transporters found?
    2. What are signs of deficiency? 4 - What are there increased levels of? 3
    3. What is the history of this fine deficiency?
    • 1. Intestines, brain, kidney, heart.
    • 2. Loss of appetite, cardiac/neurological problems, metabolic effects (increased plasma pyruvate, lactate, a-ketoglutarate)

    3. Japanese ship, nobel prize, first time accessory factors were described, first time deficiency syndrome described.
  7. Beriberi
    1. Where is it most common? Why?
    2. What are the 3 types of Beriberi? Name 3 symptoms of each.
    1. SE Asia - polished rice (def in thiamin) is a staple there.

    • 2. (1) Dry (peripheral nervous system) - neuropathy - partial paralysis, ataxia, loss of muscle function.feeling in hands and feet.
    • (2) Wet (heart) - edema, tachycardia, congestive heart failure
    • (3) Infant - rapid onset - occurs in breastfed infants with B1-def moms. Cardio/neurological systems & death due to heart failure.
  8. What are all of the possible thiamin deficiency diseases? (4)
    • 1. Beriberi (dry, wet, infant)
    • 2. Wernicke-Korsakoff's Syndrome
    • 3. Thiamin-responsive Maple Syrup Urine Disease
    • 4. Thiamin-responsive megaloblastic anemia
  9. 1. What is another name for Wernicke-Korsakoff's Syndrome?

    2. What part of world is it seen in? What is it associated with? (4)
    3. How can 1/4 of patients be treated? What's another word for this?
    4. What are symptoms of Wernicke's encephalopathy?  Name 3 out of 5
    5. What are symptoms of Korsakoff's psychosis? Name 3 out of 6
    • 1. Wet Brain Syndrome
    • 2. Developed countries - alcoholism, chemotherapy, dialysis, malabsorption
    • 3. Thiamin treatment (IV or IM) - banana bag.
    • 4. Wernicke's encephalopathy - confusion, ataxia, impaired/involuntary eye movement, paresthesia
    • 5. Korsakoff's psychosis - anterograde amnesia (can't form new memories), retrograde amnesia, hallucinations, confusion, aphonia (can't speak), confabulation (false memories/perceptions)
  10. 1. Why does chronic alcoholism lead to vitamin deficiency? (4)
    2. What is the cause of B1-responsive Maple Syrup Urine syndrome? What does this lead to --> What is the final syndrome called?
    3. Who is most often seen in? What is it characterized by? What happens if it isn't treated.
    4. How can it be treated? Why would this work?
    1. Poor nutrition, impaired vitamin absorption, impaired uptake of vitamins into cells, impaired use of vitamins

    2. Genetic mutation in BC a-keto acid dehydrogenase complex (decreased affinity of mutant for TPP leading to impaired oxidative carboxylation of branched chain AAs)

    Leads to build up BCAA (leucine, isoleucine, valine)--> leading to "branched chain ketoaciduria"

    • 3. Infants, sweet-smelling urine, coma/death.
    • 4. Large dose of B1, bc enzyme has SOME activity, just not a lot.
  11. What does a THTR mutation cause? can it be treated? If so, with what?

    Why is riboflavin called that?
    1. Thiamin-responsive megaloblastic anemia. Yes, with high dose of B1.

    2. Named for its yellow color (think flava flav)
  12. 1. What are the basic functions of B2? (4)
    2. What are the four activities of riboflavin in metabolism?
    3. What are two other activities of riboflavin outside of regular metabolism?
    • 1. Metabolism of CHOs, AAs, lipids, and antioxidant activity.
    • 2. B-oxidation of FAs (acyl CoA DH, NADH DH), TCA cycle, remove ammonia during AA deamination, coenzyme of PDH (FAD), and ETC (FMN is part of NADH DH and FADH2 delivers electrons to complex 2)
  13. 1. What are sources of B2? (4)
    2. What is it sensitive to?
    3. What are the 3 major forms and how do they differ from one another?
    4. Riboflavin in food is found in what form? Define this word
    • 1. Most animals/plants, DAIRY, enriched products
    • 2. B2 is sensitive to light.
    • 3. Free, FMN, FAD (each one has an extra phosphate group). FAD has 2.
    • 4. Riboflavins - protein complex of the coenzyme forms FMN and FAD
  14. 1. Describe bioavailability of riboflavin forms. How does this change when eating a large dose?
    2. Are animal sources or plant sources better?
    3. Describe the mechanism of transport (4)
    • 1. ~95% of all forms are absorbed regardless of ingested amounts.
    • 2. Animal
    • ____
    • 1. Flavoprotein undergoes proteolytic activity & phosphatases --> free riboflavin
    • 2. Free ribolfavin is transported into mucosal cell 
    • 3. P'lated into FMN via flavokinase (ATP DEP)
    • 4. B2 enters portal circulation as both free vitamin and FMN.
  15. 1. How is riboflavin transported in blood? (3) In what forms? (2)
    2. How does this change during pregnancy?
    3. How is riboflavin uptaken by cells? (2) What form?
    4. What happens once riboflavin is taken up?
    5. Where does most riboflavin uptake occur? Where is it tightly controlled?
    • 1. Free riboflavin and FMN via plasma proteins (globulins, fibrinogen, and weakly to albumin)
    • 2. In pregnancy, added riboflavin-binding protien (RfBP) that transports riboflavin across placenta.
    • 3. Free riboflavin is taken up by cells via Na+dep cotransporter or receptor-mediated endocytosis
    • 4. Immediately converted into coenzyme forms FMN and FAD
    • 5. Kidney, heart, liver - brain is tightly controlled.
  16. 1. How is riboflavin stored?
    2. How is riboflavin excreted? (what enzyme and what form?
    3. How does alcoholism affect this?
    • 1. No storage
    • 2. Free form via cytochrome P450
    • 3. Catabolism is accelerated in alcoholics
  17. 1. Is B2 def common in developed countries? Explain.
    2. What is often the cause of B2 def in adults?
    3. What does deficiency affect? (3)
    4. What is impaired as a result? (4) Explain last one.
    5. Why might subclinical B2 def be good
    • 1. Yes, but subclinical B2 deficiency is common - 27% of low SES teens have subclinical B2 def.
    • 2. Alcoholism and barbituates via cytochrome p450
    • 3. All tissues, but especially endothelial and neurological tissue.
    • 4. Metabolism of CHOs, AAs, lipids,  and anemia (from insufficient antioxidant defense)
    • 5. Protective against malaria and tryptophan deficiency-induced cataracts
  18. 1. What is the most common clinical presentation of B2? (1 - 3)
    2. Toxicity?
    • 1. Ariboflavinosis - inflammation of tongue, shiny, cracked lips, seborrheic dermatitis
    • 2. No
  19. 1. What are basic functions of B3? (2)
    2. What are specific functions of NADH (2) and NADPH(3)
    • 1. Biosynthesis of pyridine molecules NADH AND NADPH
    • 2. Coenzyme/substrate in many biological redox rxns in energy metabolism as electron carrier.

    • 1. ETC (donates electrons to ETC) and glycolysis
    • 2. Fatty acid synthesis, detox, antioxidant rxns
  20. 1. How does base and heat affect bioavailability of B3?
    2. Is bioavailability higher in plants or animals?
    3. What can happen if you only eat plants?
    4. What must happen to NADH and NADPH before absorption?
    5. What is the absorbed form?
    • 1. Base and heat destroy B3.
    • 2. Animals
    • 3. Deficiency
    • 4. Must be hydrolyzed by NADP+ glycohydrolase to release Nam (absorbed form)
    • 5. NAm
  21. 1. What are sources of B3?
    2. What is the form of B3 in plants and animals?
    3. What does B3 have to do with tryptophan? 4. Why is this important in the US?
    5. What else is needed to work with tryptophan? (3)
    6. What are the main forms of B3? (2) What does the backbone consist of?
    • 1. Meats (liver), fish, enriched grains, unpolished rice. Most in US comes from meat.
    • 2. NA in plants and NAm in animals in the form of NADH and NADPH
    • 3. Tryptophan can be used to synthesize niacin in human body.
    • 4. This method supplies 1/2 of niacin in US diet
    • 5. B2, B6 and Fe
    • 6. Nicotinic acid (NA) and nicotinamide (NAm) - pyridine (so requires B9).
  22. 1. How does B3 travel in blood? In what form?
    2. What is predominant form of B3 in blood?
    3. How is B3 taken up? (2) In what forms? What are special organs and why are they special? (3)
    4. How is B3 stored? (2)
    5. How is B3 excreted? Through what medium?
    • 1. Unbound as NA and NAm
    • 2. NAm
    • 3. Passive diffusion, but there are transport systems in certain organs (RBC, kidney, brain). Uptake as NA or NAm
    • 4. As NADH and NADPH
    • 5. Catabolized by NADP+ glycohydrolase and excreted in urine.
  23. 1. What are two problems that can occur from B3 def?
    2. What are 3 clinical uses of NA? How?
    3. 2 clinical uses of NAm?
    4. Why don't NA and NAm have same clinical functions?
    • 1. Pellegra and schizophrenia
    • 2. NA: antihyperlipidemic by inhibiting lipolysis (decreases VLDL, LDL and increases HDL), treating NAD-def schizphrenia, and Hartnup disease (malabsorption of tryptophan and other AAs)

    • 3. NAm = depression and anxiety
    • 4. Because they bind to different targets so will not have same effects
  24. 1. What causes pellegra?
    2. What is the course of action? (4Ds)
    3. Why did pellagra happen in the US in the 1900s?
    4. Where is pellegra still found?
    • 1. Niacin or tryptophan def
    • 2. Dermatitis, diarrhea, dementia, death
    • 3. Corn = staple and has protein that tightly binds B3 --> only 30% bioavailable
    • 4. SE Asia and Africa where polished rice = staple.
  25. 1. How does NAD def cause schizphrenia?
    2. How do affected individuals metabolize NAm differently from normal people? What is the result of this?
    3. What is a good treatment?
    • 1. Not enough pyridine nucleotides to critical areas of the brain
    • 2. They oxidize NAm more than healthy people  leading to increased excretion of an amide that is associated with hallucinations
    • 3. High doses of NA
Card Set:
Vitamin B1-B3
2013-03-06 06:45:07

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