Vitamins Flashcards
Is Vitamin A water soluble or fat soluble?
fat
All vit A are classified as
retinoids
What are the 3 pre-formed forms of Vit A?
-Retinol
-Retinal
-Retinoic acids
Which form of Vit A is important in vision?
Retinal
What is the active form of Vit A in transcriptional regulation?
retinoic acid
What are precursors to Vit A?
carotenoids
What form of Vit A can carotenoids be cleaved in to?
retinal
What are the two forms of retinoic acid?
all-trans retinoic acid and 9-cis-retinoic acid
What form of vit A is only found naturally in animal products?
pre-formed retinoids
where are all the provitamin A found?
carotenoids are found in plants
What must occur before vit A can be absorbed?
-provitamin a are cleaved into retinal via carotene dioxygenase
-retinal is reduced to retinol, esterified and secreted into chylomicrons together with dietary retinol
Why must retinoids be packaged into chylomicrons?
because they are fat soluble so they must be attached to a lipoprotein in order to cross the intestinal membrane
In what form is retinol stored?
as retinyl esters
Where is retinol stored?
the liver
How is retinol transported in blood?
via retinol binding proteins
What happens to retinol once it is carried to tissues via RBPs?
it is oxidized to retinoic acid (active form)
Explain the role of retinal in vision
- In the retina, when light strikes rhodopsin (contains retinal) it isomerizes 11-cis-retinal to 11-trans-retinal, signal then passes to a g-protein (transducin) triggering a series of events. the rod hyper polarizes which leads to the perception of light
What is the mechanism of action of retinoic acid?
both all-trans and 9-cis-retinoic acid bind to nuclear receptors, which then alters gene expression
What are the two retinoic acid receptor families?
retinoic acid receptor and retinoic acid x receptors
Which receptor binds BOTH all-trans and 9-cis- retinoic acid?
retinoic acid receptors
Which receptor binds ONLY 9-cis-retinoic acid?
retinoic acid x receptor
although not common, list 5 results of vit A deficiency
-blindness
-increased susceptibility to infectious diseases
-maternal mortality and poor pregnancy outcomes
-decreased growth rates and bone development in young
-reptiles and birds: conjunctivitis, periocular inflammation
True/false: vit a deficiency is more of a problem/common than toxicity?
false
What is the main result of Vit. A toxicity?
cell lysis and tissue damage
What is hypervitaminoisis A usually related to?
Dietary reasons
What is the most common sign of hypervitaminosis A?
skeletal abnormalities/ bone issues
Is Vit D water or fat soluble?
fat
Is Vit D strictly a vitamin? if not, why not?
No, because it can be synthesized in the skin with UV light exposure.
What is the main biologic function of the active form of Vit D
It acts as a hormone in the regulation of calcium absorption and homeostasis
What is the active form of Vit D?
calcitriol
What are the major class of enzymes that active Vit D?
cytochrome proteins (hydroxylases)
What two organs are involved in the activation of Vit D?
liver and kidney
What are the two dietary sources of Vit D?
Ergocalciferol (D2): found in some plants and fungi
Choleocalciferol (D3): animal sources
Where is dietary vit D absorbed?
intestine
How is both dietary and synthesized vit D transported in the blood?
Vitamin D binding proteins (DBP)
What are the 3 target organs of vit D?
kidney, intestine, bone
How are calitriol actions carried out/mediated?
the nuclear receptor (VDR)
How does calcitriol regulate calcium homeostasis?
Maintains serum concentration by:
-Increases calcium absorption in the intestine
-reduces excretion of calcium by stimulating reabsorption in the distal renal tubules
-mobilization of calcium from bone
What are the 4 other biologic actions of calcitriol outside of calcium mediation?
-cell differentiation and proliferation
-synthesis and secretion of parathyroid and thyroid hormones
-immune function
-bone development and remodeling
What are the key points of calcitriol production (aka Vit D activation)?
-up-regulation of low serum calcium and phosphate
-self regulation by stimulating 24-hydroxylase (inactivation) and inhibiting 1-hydroxylase
What are the main signs of Vit D deficiency?
hypocalcemia, muscle weakness, immune dysfunction, bone issues
What are the signs of hypervitaminosis D?
Hypercalcemia, calcification of soft tissues, kidney disease, uroliths
Calculate a toxic dose of Vit D
toxic dose: >100ug/kg
40IU=1ug
most supplements are 400IU
Is Vit E water or fat soluble?
fat
Describe the antioxidant action of Vit E
Acts as a lipid soluble antioxidant in cell membranes and for serum lipoproteins by free radical scavenging, it will donate an H atom to radicals, this in turn forms an oxidized radical which can be reduced by other antioxidants
What is the active form name of Vit E
Tocopherol
How do ROS affect the phospholipid bilayer?
affects the structure and permeability
Which fatty acids are sensitive to oxidative damage?
unsaturated fatty acids
Why would you supplement vit E if an animal routinely is supplemented omega- 3 fatty acids?
Since unsaturated fatty acids are more susceptible to free radical damage, vit. e supplementation will help prevent degradation.
List two ways tocopherol radicals (post antioxidant actions) can be addresses?
-reduced back by other antioxidants
-can be conjugated to then be excreted in bile
Why is Vit E less likely to result in toxicity compared to other fat soluble vitamins?
Because it can be routinely conjugated and excreted in bile
What disease in lambs and calves can be caused by vitamin E deficiency?
white muscle disease
Describe white muscle disease
because of the deficiency, free radicals produced by muscle use will build. free radials will bind to calcium. Calcium will then deposit and cause white streaks in the muscles
Is vitamin K water or fat soluble?
fat
How was vitamin K discovered?
result of investigation into the cause of a bleeding disease in cattle and chickens
What is the main function of vit K?
required for blood clotting
What is the active form of vit k?
hydroquinone
is the active form of vit k water or fat soluble?
water!
What is the role of hydroquinone in clotting protein formation?
It is required for the post-translational modification of glutamate residues in clotting proteins
carboxylated glutamate (Gla) has the ability to do what?
chelate calcium
What does binding calcium permit clotting proteins to do?
promotes the binding of the proteins to to phospholipid surfaces inside blood vessels
What are two vit k antagonists?
Dicumarol and Warfarin
What important information do you need to you treat rodenticide poisoning?
Which type of rodenticide it is
How does warfarin inhibit clotting?
It inhibits 2,3 epoxide reductase (VitK reductase)
Describe the hepatic vit k cycle
Vit K -> hydroquinone-> 2,3 epoxide via 2,3 epoxide reductase -> vitamin K
What kind of inhibitor is warfarin and dicumarol?
competative
For what species is Ascorbic acid a vitamin?
primates, guinea pigs, bats, most fish, songbirds
What pathway synthesizes ascorbic acid?
Uronic acid pathway
What are the 3 main actions of vitamin C?
-Cofactor for hydroxylation reactions
-Powerful reducing agent
-Enhances intestinal absorption of iron
What reactions is ascorbic acid needed for?
-Dopamine hydroxylase
-proline and lysine hydroxylases
-carnitine synthesis
How does ascorbic acid enhance the absorption of iron?
It redices Fe3+ to the more easily absorbed Fe2+ form
Is Ascorbic acid water or fat soluble?
water
What is the main antioxidant activity of ascorbic acid?
It is the primary defense against aqueous radicals in the blood?
What enzyme converts L-ascorbate back to ascorbic acid?
glutathione peroxidase
What is the main disease associated with vit c deficiency?
scurvy
What are the main signs of scurvy?
-gum recession and bleeding
-bruising
-fragility of capillaries
-bone fracture
-psychological changes
Is thiamine (B1) water or fat soluble?
water
What is the key role of thiamin?
plays a key role in carbohydrate metabolism
What are the two main reactions that require thiamin?
-Oxidative/reduction reactions
-Transketolase reactions (ex HMS)
What typically causes thiamin deficiency?
thiamases
What are thiaminases and where are they mainly found?
They degrade thiamin and they are found in raw rish/shellfish (produced by microbes)
Is riboflavin (B2) water or fat soluble?
water
What are the two coenzymes riboflavin is a precursor for?
FMN and FAD
What are the roles of flavin coenzymes?
they are electron carries in oxidation/reduction rxns
What enzyme is uric acid formation is dependent on a rioboflavin derivative?
xanthine oxidase
Why are there no serious signs of riboflavin deficiency?
Because the body is very efficient in its use. Once it is release by catabolism of enzymes it is quickly incorporated into new ones
Is niacin water or fat soluble?
water
What are the two forms of vit B3
Niacin and niacinamide
Why is niacin so critical?
It is a component of NAD and NADP
What reactions are niacin derivatives part of?
oxidation/reduction rxns
Where is niacin mainly absorbed?
small intestine
Why is niacin not strictly a vitamin?
niacinamide can be synthesized from tryptophan in the liver of most mammals
What amino acid is niacin a derivative of?
tryptophan
what species CAN NOT synthesize niacin?
cats
Which vitamin and what form would you use as a treatment for inflammatory or autoimmune skin conditions in dogs such as cutaneous lupus or pemphigus
niacin, specifically niacinamide
Why would you NOT use specifically niacin as a supplement in animals?
Because it has a different profile to niacinamide and can cause signs such as skin flushing, dizziness, tachycardia, nausea, liver damage at high doses
What are the 2 main coenzymes derived from pentothenic acid?
CoA
4-phosphopentatheine
Is pentothenic acid (Vit B5) water or fat soluble?
water
What component provides coenzyme A with its sulfur group?
cysteine
What 2 types of pathways utilize CoA? give examples
-Carbohydrate metabolism: Acetyl CoA, Succinyl CoA, Propionyl CoA
-Lipid metabolism: Acyl-CoA, HMG-CoA
Is pentothenic acid deficiency common or rare?
rare
Is Biotin (B7) water or fat soluble?
water
What rxns is biotin a coenzyme in? (3)
-Acetyl CoA carboxylase (fatty acid biosynthesis)
-Propionyl CoA carboxylase (propionate to succinyl coa)
-Pyruvate carboxylase (pyruvate to OAA)
Where can biotin be synthesized?
microflora in the intestine
Why can raw egg white ingestion be a problem?
It contains avidin which will bind to biotin in the gut and prevent absorption
Which vitamin can be used as a reagent in biochemical assays to detect proteins and nucleic acids?
Biotin
What has to happen to biotin before it can be used as a coenzyme in carboxylation rxns?
it must be carboxylated itself
What is the active form of biotin?
carboxybiotin
What is the most common active form of B6
Pyridoxal phosphate
What rxns (4) require vit B6 (pyridoxal phosphate)
-Glycogen phosphorylase
-AA metabolism
-Heme/porphyrin metabolism (delta-ALA synthase)
-Niacin synthesis from tryptophan
What neurotransmitter synthesis requires pyridoxal phosphate?
GABA
Formation of N5,N10 methylene THF requires what coenzyme?
Vit B6
Where does cobalamin get its name?
the cobalt in the center of the porphyrin ring
Where do you get cobalamin (Vit B12)?
Animal sources only
What synthesizes Vit B12
microorganisms
What causes the color of cobalamin?
the porphyrin ring
Where is Vit B12 absorbed?
distal intestine
What glycoprotein is required for cobalamin absorption?
Intrinsic factor
Where is intrinsic factor made?
gastric parietal cells and by pancreatic ductular cells in dogs and cats
What protein allows B12 uptake by the liver?
transcobalamin II (TCII)
Where can cobalamin be stored?
the liver
What must cobalamin be bound to to be stored?
transcobalamin I (TCI)
What two rxns require cobalamin?
-proprionate->methylalonyl CoA ->succinyl CoA
-homocysteine -> methionine which releases THF which is needed for nucleic acid synthesis
What are 5 causes of B12 deficiency?
-Dietary
-Gastric disease
-Pancreatic disease
-Ileal disease
-Liver Disease
What are the main diseases that in turn cause B12 deficiency
-Resection or IBD
-Overgrowth of cobalamin binding bacteria
What disease can result from vit B12 deficiency
Megaloblastic anemia
