vitamins2 Flashcards
vit K1=
phylloquinone, from plants
vit K2=
menaquinone, from fish
menadione=
synthetic form of vit K that is water soluble- converted to active form via prenylation in the liver
role of vit K in clotting
cofactor for the carboxylation of glutamate to make g-carboxyglutamate, that binds Ca
role of vit K in bone development
acts on osteocalcin (bone protein), to help it bind Ca
2 enzymes that help to recycle vit K via reduction
- vit K epoxide reductase
- vit K reductase
inhibitors of the bit K reductases
warfarin
reason that most newborns have vit k def
bc intestinal bacteria is a major source of vit K and neonates are not yet colonized
excess menadione will cause-
hemolytic anemia and jaundice d/t liver toxicity
is intestinal synthesis of vitamin K sufficient?
no, also need from the diet
form of vitamin a that is part of visual pigment
11-cis retinal
enzyme that converts retinol –> all-trans retinal
retinol dehydrogenase
enzyme that converts all-trans retinal –> 11-cis-retinal
retinal isomerase
enzyme that converts all-trans retinal–> retanoic acid
retinal dehydrogenase
which forms of vitamin a participate in gene transcription?
all-trans retanoic acid (RXRs and RARs)
9-cis-retinoic acid (RXRs only)
what is unique about the conversion of retinal to retinoic acid?
rxn is irreversible, thus retinoid acid is NOT involved in the visual cycle
what 2 elements combine to forms rhodopsin?
- opsin
- 11-cis-retinal
describe the process of light transmission in vision
- light energy converts rhodopsin to all-trans-retinal and opsin
- transducin will activate cGMP phosphodiesterase the results in closure of Na channels
- hyperol results = signal to brain
- dehydrogenase converts all-trans back to 11-cis
what “super family” is retinoid acid part of?
steroid, all have intracellular receptors with a DNA binding domain
which form of retinoic acid receptor can form heterodimers? what can it heterodimerize with?
RXRs; vit D receptor, thyroid hormone receptor, PPAR receptor
where is vitamin a stored?
as retinal esters in stellate cells of the liver
how is vitamin a released from the liver?
bound to retinal binding protein in a “trimolecular” complex with transthyretin (pre albumin) and T4
how is excess vitamin a excreted?
add b-glucuronate and excreted in bile
first sx of vitamin a def
night blindness (due to lack of 11-cis-retinal)
xerophthalmia occurs due to the lack of ___ (specifically)
retinoic acid
what is the processing that happens with b-carotene? where?
b-carotene –> retinal –> retinol
mainly in intestine
some b-carotene is not cleaved before it is absorbed, what happens to that?
it functions as an antioxidant, but has no vitamin a activity
excess vitamin a vs. excess b-carotene
excess vitamin a = liver damage, teratogen
excess b-carotene= yellow skin
lycopene can decrease ___
colon CA
lutein can help with prevention of ___
age related macular degeneration because it inhibits oxidation of cell membrane
how is cholecalciferol formed?
reaction of 7-dehydroxycholesterol and UV light
D2=
ergocalciferol (plant form)
major circulating form of vitamin D is-
25-hydroxy vit D
where is 25-hydroxy vitamin D made?
liver by 25-hydroxylase
what is the active form of vitamin D?
1,25-dihydroxy vitamin D, made by 1a-hydroxylase in kidney, aka calcitrol
what is the inactive form of vitamin D?
24,25-dihydroxy vitamin D
roles of calcitriol (5)
- ca absorption in gut
- Calcium/phosphate balance
- bone growth/remodeling
- neuro/immune function
- gene expression (cell proliferation/death)
at risk for vitamin D def (6)
- decreased sun exposure/sunscreen
- darker skin pigments
- over 50 (dec ability to synthesize in skin/dec activation by kidney)
- breastfed infants
- CKD or liver dz
- taking meds that induce CYP450 (inactivate 1,25)
what is the form of vitamin D supplement that must be given to pts with CKD or liver disease?
active form (calcitrol/1,25-dihydroxy vitamin D)
active form of vitamin E
a-tocopherol
what is aTTP?
a-tocopherol transfer protein, transferstocopherol from liver into VLDL for transport to other tissues
what is the main action of vitamin E?
acts as free radical scavenger and protects PUFA in membrane
what is a cofactor in regeneration of the reduced form of a-tocopherol?
vitamin C
consequence of vitamin E def
hemolytic anemia due to increased RBC fragility; nerve degeneration in hands and feet
