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25 Cards in this Set
- Front
- Back
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What is the active form of Vitamin C?
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Ascorbate
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Give the sound byte for Vitamin C.
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Vit C is a reductant that participates in hydroxyalse reactions
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What is a hydroxylase reaction?
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One that transfers an O to a substrate (can transfer or one two O's)
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What are the forms in which Vit C is found?
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Ascorbic acid (all OH)
Monodehydroascorbate (one O•) Dehydroascorbate (both =O) |
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In bird/mammals, what is Vit C derived from? What animals cannot make Vit c?
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Glucose
Cannot: humans, primates, guinea pigs, indian fruit bat |
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What enzyme are humans lacking in the pathway to synthesize Vit c?
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Gulanolactone Oxidase
(gulanolactone -> ketogulanoloactone) |
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How is Vit C absorbed?
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Active transport: SVCTI and SVCTII (sodium dependent Vitamin C Transporters): 80-90% depending on dose. Different transporters in diff. locations. #1: instine, liver, kidney
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SVCT I absorbs what?
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Ascorbic acid; low affinity for dehydroascorbate
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In what form is Vit C found in blood?
How is it taken up into a cell? |
Ascorbate•albumin complex (bound to proteins)
SVTC transporters absorb it in ascorbic acid form and then dehydroascorbate reductase reduces it again into ascorbate. |
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How is Vit C extreted?
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Pee: 3 common forms, ascorbate/dehydroascorbate; one oxidized form of dehydroascorbate (diketogulonic acid) and 50% as oxalate
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How does the body handle high doses of Vit C?
What is the renal threshold? |
Renal thershold of 1mg/100ml - once this is exceeded, excess pours into urine
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What is the main biochemical function of Vit C?
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Acting as a reductant in hydroxylase reactions.
Monooxygenase and dioxygenase rxns. |
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What are two important monooxygenase reactions?
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Dopamine --> Norephinephrine
and a-amidation reactions that activate peptide hormones/ hormone releasing factors. Some include CCK, calcitonin, gastrin, vasopressin. NOTE!!! Ascorbate only participates in ONE (1st?) step of reaction |
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Besides Vit C, what is required for monooxygenase reactions?
What about for dioxygenase reactions? |
Mono: Cu and O2
Di: Fe and a-ketoglutarate and O2 |
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What form does Vit C participate in monooxygenase reactions?
What is its role? |
Ascorbate
It reduces Cu again (enzyme of rxn is Cu dependent) Ascorbate -> monodehydroascorbate |
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Name the two enzymes that participate in monooxygenase reactions
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dopamine b-hydroxylase
and peptidyl glycine hydroxylase |
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What do a-amidation reactions do?
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1st stage in overall reaction that activates peptide hormones (CCK, gastrin, calcitonin) & hormone releasing factors by replacing COOH end with NH2.
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Enzyme for a-amidation reaction?
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Peptidyl glycine hydroxylase
(at least remember hydroxylase) |
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What are two examples of dioxygenase reactions?
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Prolyl and Lysyl hydroxylases
In general, these reactions are involved in stabilizing collagen and pro-collagen, for example. |
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Why is ascorbate not used stoicheometrically in dioxygenase reactions?
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Because it reduces only the ferrous form of iron, which doesn't always get produced
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What are signs of Vit C deficiency?
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Capillary fragility due to high histidine levels - hemmoraging
Impaired wound healing Weakening of collagenous structures in bones, teeth lethargy pithed frog |
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How quickly can sign of Vit C deficiency appear?
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45-80 days
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Assesment of Vit C levels?
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No functional test; plasma ascorbate measured
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Vit C in foods? Losses?
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Citrus fruits, leafy greens.
Oxidation during storage and losses during cooking (via H20) |
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Why is hemorrhaging common with Vit C def?
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Because the breakdown of histadine requires Vit C. High levels of histidine cause capillary fragility.
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