Metabolism II > Vitamin C > Flashcards

Vitamin C Flashcards

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1
Q

What was written by James Lind in 1753, that showed that scurvy was easily treated with citrus fruits?

A

Treatise of the Scurvy

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2
Q

What do plants synthesize Vitamin C from?

A

glucose & fructose

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3
Q

Most mammals can synthesize Vitamin C from glucose in their…

A

liver or kidneys

  • Most mammals: dogs, cats, mice, cows, horses
  • Reptiles
  • Amphibians
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4
Q

Why can’t mammals synthesize Vitamin C?

A

Lack the enzyme to convert glucose to Vitamin C

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5
Q

Where is fat soluble Vitamin C stored in the body? (3)

A
  • Adrenal gland
  • Pituitary gland
  • Eyes
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6
Q

Vitamin C = ________ = ascorbate

A

L-ascorbic acid

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7
Q

L-ascorbic acid (ascorbate) is what kind of acid?

A
  • Weak acid

- 6 carbon alpha-ketolactone

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8
Q

Vitamin C can donate what to other compounds which are at risk of becoming oxidized.

A

2 electrons

  • Vitamin C is an electron donor, which makes it a reducing agent
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9
Q

Why is Vitamin C known as an outstanding antioxidant?

A
  • Its reduction potential as an electron donor is very high.

- Readily “gives up” electrons

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10
Q

How is Vitamin C assessed?

A

Serum Ascorbic Acid levels

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11
Q

Serum Ascorbic Acid levels are …

A

Dose-dependent

*No further increase following additional doses of VIt. C

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12
Q

What is Serum Ascorbic Acid levels lowered by? (7)

A
  • Smoking
  • Oral contraceptive use (birth control)
  • Cold
  • Fever
  • Acute or chronic stress
  • Infection
  • Inflammatory Bowel Disease
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13
Q

What 2 ways can Vitamin C be absorbed?

A

Active transport & Simple diffusion

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14
Q

Where does the active transport of Vitamin C occur?

A

Active transport occurs through out the small intestine.

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15
Q

Simple diffusion of Vitamin C occurs with?

A

Simple diffusion occurs with higher intake of Vitamin C

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16
Q

Absorption of Vitamin C is modulated by what?

A

Glucose transporters (GLUT)

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17
Q

What form of Vitamin C is typically absorbed more in the lumen?

A

Dehydroascorbate

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18
Q

Dehydroascorbic acid (DHAA) is converted to ascorbate in enterocytes via?

A

DHAA reductase

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19
Q

In what form does Vitamin C circulate?

A

Freely, unbound to any proteins

*Water-soluble nutrient available for cellular transport and accumulation inside tissues.

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20
Q

Vitamin C is uptaken into cells via?

A

SVCT1 & SVCT2 - sodium-dependent Vitamin C transporters

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21
Q

Both SVCTs are dependent on what?

A

Na & ATP

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22
Q

Neither of the SVCTs transport …

A

Dehydroascorbic acid

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23
Q

In what forms is Vitamin C excreted as?

A

intact or in form of metabolites

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24
Q

Where does the metabolism of Vitamin C occur?

A

Liver & also kidney

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25
What are the final excretory products of Vitamin C metabolism? (2)
Oxalic acid & 4-C threonic acid
26
Vitamin C can also be excreted as ...
A variety of 5-C sugars | - Xylose, xylonate, lyxonate
27
Ascorbic acid concentrations in plasma are tightly regulated by what?
Kidney
28
What patients is Vitamin C excretion problematic?
End-stage renal disease
29
Why is Vitamin C excretion problematic in patients with end-stage renal disease?
Due to lack of glomerular filtration
30
In patients with end-stage renal disease Vitamin C doses higher than 200mg can accumulate and produce?
hyperoxalemia
31
Why do dialysis patients often have chronically low plasma Vitamin C concentrations?
To prevent to much oxalate formation in the blood. | * hyperoxalemia
32
Vitamin C is required as a cofactor for how many different enzymes?
8
33
What are the 2 families of enzymes that require Vitamin C as a cofactor?
Monooxygenases & Dioxygenases
34
What incorporates a single oxygen molecule into a substrate?
Monooxygenases
35
What enzyme is responsible for: | Dopamine -> Norepinephrine synthesis
Dopamine Beta-monooxygenases
36
What incorporates molecular oxygen (O2) into a substrate?
Dioxygenases
37
Dioxygenases adds hydroxyl groups to ____ or ____.
Proline or lysine
38
Adding hydroxyl groups to proline or lysine for the ...
formation of collagen molecule
39
Dioxygenases are used in the biosynthesis of ...
Carnitine
40
What is carnitine is essential for?
Fatty acid transport into mitochondria
41
Dioxygenases are used in the metabolism of?
Tyrosine
42
What symptoms are related to the impaired function of these two families of enzymes? * (Especially in impairment of collagen formation)
Scurvy symptoms
43
Vitamin C acts as an antioxidant by preventing intracellular?
Protein oxidation
44
The prevention of intracellular protein oxidation is relevant in which tissues with high oxidant production?
- Neutrophils - Monocytes - Macrophages
45
The prevention of intracellular protein oxidation is relevant in which tissues with high oxygen concentrations?
- Lungs | - Tissues of the eye exposed to light
46
Vitamin C acts as an antioxidant extracellularly by preventing?
Oxidant-mediated damage extracellularly
47
Vitamin C prevents oxidant-mediated damage extracellularly by quenching ... (2)
- Aqueous peroxyl radicals | - Lipid peroxidation products (rancid fats)
48
Vitamin C is preferentially used before what? (3)
- Tocopherols (Vit. E) - Bilirubin - Uric acid
49
Vitamin C affects several pathways involved in what?
Atherogenesis
50
Vitamin C protects LDL from what?
Metal catalyzed oxidation * Hypothesized to be an initiating factor in atherogenesis
51
Vitamin C can regenerate oxidized ...
alpha - tocopherol (Vitamin E)
52
Vitamin C affects several pathways involved in atherogenesis, and can decrease ...
Lipid peroxidation
53
Vitamin C can decrease adhesion of ______ to endothelium of vascular system?
Monocytes
54
Vitamin C can decrease aggregation of ______ & _______.
Platelets and leukocytes
55
Vitamin C can quench oxidants that 'leak' from activated ______ or ______, which prevents damage to supporting tissues such as collagen and surrounding fibroblasts.
Neutrophils or macrophages
56
Vitamin C is involved in cholesterol degradation for ...
Bile acid synthesis
57
What retards cholesterol transformation into bile acids?
Vitamin C deficiency
58
What has been implicated as a risk factor in CVD?
Hypovitaminosis C
59
Vitamin C is involved in the conversion of folacin to
Tetrahydrofolate (THF)
60
Vitamin C is involved in the synthesis of
adrenal tissue steroids (noradrenaline)
61
Vitamin C helps iron absorption by ...?
- reducing ferric to ferrous form | - and is involved in transfer from plasma transferrin to liver ferritin
62
Vitamin C improves immune response by increasing? (4)
- Immunologic activity of leukocytes - Interferon production - Integrity of mucous membrane - Processes of inflammatory reactions
63
What was found to be lower in HIV subjects?
Plasma ascorbate
64
What treatment is commonly used in HIV subjects?
Interferon treatment
65
Tolerable upper limit was set due to what at higher doses?
Gi adverse affects
66
Who is at risk for deficiency? (3)
- Smokers - Individuals with limited food variety - Females using oral contraceptives
67
Smokers have lower ____ & _____ vitamin C levels, and require additional 35mg/day of vitamin C.
plasma & leukocyte
68
What are the best sources of vitamin C?
Fruits and vegetables
69
What are the earliest symptoms of scurvy?
Weakness & lassitude (a state of physical or mental weariness; lack of energy)
70
A symptom of vitamin C deficiency results in an autoimmune disease in which sufferers experience dry mouth & dry eyes.
Sjogren's Syndrome
71
Ingestion of 3g of Vitamin C or more per day can cause what? (4)
- Osmotic diarrhea - Bloating - Hyperuricosuria - Iron overload in certain cases
72
Presence of excessive amounts of uric acid in urine, associated with kidney stones.
Hyperuricosuria
Metabolism II
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