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why do water-soluble vitamins have less risk of toxicity
- because they dissolve in water
- are readily excreted
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what is an apoenzyme
inactive enzyme form
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what is a holoenzyme
active enzyme, formed when apoenzyme and coenzyme come together
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enrichment vs fortification
- enrichment - addition of nutrients that were lost during processing
- fortification - addition of nutrients into processed foods whether they were part of the food or not
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4 function of thiamin (B1)
- thiamin pyrophosphate (TPP) is a coenzyme in the metabolism of carbohydrates, branched chain AAs, and pentoses
- helps convert pyruvate to acetyl CoA for citric acid cycle
- synthesis of neurotransmitter acetylcholine
- helps with synthesis of RNA
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sources of thiamin
- pork
- sunflower seeds
- legumes
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how is thiamin absorbed, transported, stored, excreted
- A - in the jejunum by carrier mediated system
- T - by RBC in the blood in its coenzyme form
- S - small reserve in liver and muscles, poor storage
- E - excess quickly excreted in urine
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2 main deficiency diseases of thiamin
- Beriberi - dry, wet, infantile. occurs where polished rice is the only staple, occurs within 7 days, neuro/cardiovasc problems
- Wernicke-Korsakoff syndrome - aka cerebral beriberi, alcohol diminishes absorption and increases thiamin excretion
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structure of riboflavin
three linked 6-membered rings with sugar alcohol attached to middle ring
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3 functions of riboflavin
- energy metabolism in citric acid cycle
- helps activate other B vitamins to their active forms
- antioxidant
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co-enzymes of riboflavin
- flavin monoculeotide (FMN)
- flavin adenine dinucleotide (FAD)
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sources of riboflavin
- a quarter from milk products
- enriched grains
- eggs
- meat
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what destroys riboflavin
UV light and radiation, but it is stable in heat
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how is riboflavin digested, absorbed, transported, stored, and excreted
- D - Hcl in stomach releases riboflavin from its bound form
- A - active or facilitated transport during low to moderate intake, but passive absorption during high intake
- T - by protein carrier in the blood
- S - small amount stored in lover
- E - excess secreted can cause urine to turn bright yellow
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main riboflavin deficiency disease
- ariboflavinosis
- alcoholics, users of phenobarbital, avoidance of milk products
- symptoms - glossitis, stomatitis, seborrheic dermatitis, affects mouth, skin, RBCs
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what is B3 and its two forms
- niacin
- nicotinic acid (niacin)
- nicotinamide (niacin amide)
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function of niacin/B3
- synthesizes NAD+ and NADP+
- coenzyme in oxidation-reduction reactions (glycolysis, CTA, fatty acid synthesis)
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food sources of niacin
poultry, meat, fish, mushrooms
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what can niacin be synthesized from
- tryptophan
- found in protein rich foods
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1 mg niacin = _____ mg tryptophan
60 mg
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1 gram of protein = _____ mg tryptophan
10 mg
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what is NE (the unit)
niacin equivalents
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how is niacin absorbed, transported, stored, and excreted
- A - readily absorbed from stomach and SI, active and passive
- T - from liver to all of the tissues where it is converted to coenzymes
- E - excess excreted in urine
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niacin diseases, 3 D’s, susceptible populations
- pellagra - diarrhea, dementia, dermatitis
- can be prevented with adequate protein diet
- those who consume corn as main staple are susceptible + alcoholics
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what is hartnup disease
rare genetic disorder where tryptophan to niacin pathway is blocked
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toxicity effects of niacin
- flushing of skin
- itching
- nausea
- liver damage
- UL = 35 mg
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functions of pantothenic acid
- part of coenzyme A (for formation of acetyl coA for citric acid cycle)
- forms acyl carrier protein involved in fatty acid elongation
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food sources of pantothenic acid
- meat, milk, many veggies
- freezing, canning, refining will destroy PA
- unprocessed foods are better sources
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deficiency for pantothenic acid
rare
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ATSE of pantothenic acid
- A - absorbed as pantothenic acid from SI
- S - minimal storage as coenzyme in liver
- E - readily excreted in urine
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pantothenic acid deficiency diseases
- rare
- burning foot syndrome
- fatigue
- HA
- alcoholics at risk
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function of biotin
- cofactor in carboxylase reactions (adds CO2 to compounds)
- formation of oxalacetate
- fatty acid synthesis and breakdown
- allows for breakdown of AA for use as energy
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ATSE for biotin
- A - exists in free and protein bound forms (biocytin), which has to be cleaved from protein by biotinidase before being absorbed in SI
- S - stored in small amounts in muscle, liver, and brain
- E - excreted via urine and bile
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what can cause biotin deficiency
- rare
- high intake of raw eggs bc it has Avidin -> which inhibits absorption
- alcoholism
- anticonvulsant drug use
- biotinidase deficiency
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what are the 3 forms of Vitamin B6 and how are they activated
- pyridoxal
- pyridoxine
- pyridoxamine
- the 3 forms can be phosphorylated to become active vitamin B6 coenzyme
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main coenzyme form of B6
pyridoxal phosphate (PLP)
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function of Vitamin B6
- decarboxylation of AA
- transamination reaction
- rearrangement of AA
- conversion of tryptophan to niacin
- helps regular blood glucose level
- needed to make red blood cells and hemoglobin
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food sources of B6
- meat
- fish
- poultry
- carrots, potato, oatmeal
- spinach
- more readily absorbed from animal foods
- lost during resining of grains
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ATSE of vitamin B6
- A - passively, all 3 forms phosphorylated in liver
- T - binds to albumin for transport in blood
- S - stored in liver and muscle tissue
- E - through urine
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B6 deficiencies
- rare
- microcytic hypochromic anemia - small, pale RBCs that have decreased oxygen carrying abilities
- reduced immune function
- peripheral nerve damage
- susceptible to alcoholics, ppl with genetic defect for anemia, medication interactions
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function of folate
- influences DNA methylation
- DNA synthesis
- AA metabolism
- neurotransmitter synthesis
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sources of folate
- liver
- legumes
- leafy greens
- susceptible to heat, oxidation, UV light
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what is DFE and how is it calculate
- dietary folate equivalents
- DFE = (total synthetic folate x 1.7) + total food folate intake
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ASE for folate
- A - to be absorbed has to be broken down into mono glutamate in GI tract with the help of folate conjugase
- S - mainly liver, once transported into cell it is converted into polyglutamate form so it is trapped in cell
- E- in ruine and bile
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2 main folate deficiencies
- megaloblastic anemia - larger than normal RBCs, unable to divide or make it out of bone marrow, aka macrocytic anemia
- neural tube defects -> spina bifida or anencephaly
- susceptible ppl = alcoholics and pregnant women bc increased rate of cell division and DNA synthesis in mother and baby
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3 forms of vitamin B12
- cyanocobalamin (free vitamin B12)
- methylcobalamin (coenzyme form)
- 5-deoxyadenosylcobalamin (coenzyme)
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only vitamin that contains cobalt
B12
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functions of vitamin B12
- formation of methionine and homocysteine AAs
- coenzymes move 1-carbon groups in CTA, oxidation of FAs, folate metabolism
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sources of B12
- animal products
- vulnerable to heat
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ATSE for B12
- A - free vitamin B12 binds to R-protein from salivary gland, released by HCL and pepsin in stomach, binds to IF, this complex binds to boarder cell receptors for absorption
- about 50% absorbed
- T - transcobalamin II binds to absorbed vitamin B12, transports it through portal vein, taken up by liver, bone marrow, RBCs
- S - 50-90% of body’s supply is stored in liver
- E - very little through bile, reabsorbed by enterohepatic circulation
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what can disrupt vitamin B12 absorption
- absence or defective synthesis of R-protein, IF, or pancreatic proteases
- defective binding to IF
- removal of ileum or stomach
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2 vitamin B12 deficiency diseases + treatment
- pernicious anemia - decrease in RBS when body cant properly absorb B12 bc of lack of production of IF
- macrocyctic anemia - too much homocysteine can damage endothelial cells
- treatment = monthly injections, nasal gel, oral doses
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why is choline not a B vitamin
bc it does not have coenzyme function
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function of choline
- precursor for compounds that enable cell membranes to form
- involved in export of VLDL from liver -> prevents it from accumulating in liver
- assists in conversion of homocysteine to methionine -> another way to decrease homocysteine levels
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what is lecithin
component of cell membranes that helps make myelin for nervous system
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food sources of choline
- in form of lecithin
- milk
- liver
- eggs
- peanuts
- animal sources are largest sources
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deficiency of choline
rare
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ASE for choline
- absorbed from SI via transport protein
- all tissues store and contain choline
- some excreted in urine
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two forms of vitamin C
- ascorbic acid (reduced)
- dehydroascorbic acid (oxidized)
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functions of vitamin C
- antioxidant
- collagen synthesis
- enhances non heme iron absorption
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sources of vitamin C
- fruit
- veggies
- fortified cereals
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ASE of vitamin C
- A - by specific energy dependent transport system in SI, passive if intake is high, decreased absorption if intake is high
- S - high content stored in pituitary and adrenal glands, WBC, brain, eyes
- E - via kidneys
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vitamin C deficiency disorder
scurvy
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what inhibits vitamin C absorption
pectin and zinc
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