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Metabolism II > Vitamin C > Flashcards

Vitamin C Flashcards

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
Q

What are the final excretory products of Vitamin C metabolism? (2)

A

Oxalic acid & 4-C threonic acid

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26
Q

Vitamin C can also be excreted as …

A

A variety of 5-C sugars

- Xylose, xylonate, lyxonate

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27
Q

Ascorbic acid concentrations in plasma are tightly regulated by what?

A

Kidney

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28
Q

What patients is Vitamin C excretion problematic?

A

End-stage renal disease

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29
Q

Why is Vitamin C excretion problematic in patients with end-stage renal disease?

A

Due to lack of glomerular filtration

30
Q

In patients with end-stage renal disease Vitamin C doses higher than 200mg can accumulate and produce?

A

hyperoxalemia

31
Q

Why do dialysis patients often have chronically low plasma Vitamin C concentrations?

A

To prevent to much oxalate formation in the blood.

* hyperoxalemia

32
Q

Vitamin C is required as a cofactor for how many different enzymes?

A

8

33
Q

What are the 2 families of enzymes that require Vitamin C as a cofactor?

A

Monooxygenases & Dioxygenases

34
Q

What incorporates a single oxygen molecule into a substrate?

A

Monooxygenases

35
Q

What enzyme is responsible for:

Dopamine -> Norepinephrine synthesis

A

Dopamine Beta-monooxygenases

36
Q

What incorporates molecular oxygen (O2) into a substrate?

A

Dioxygenases

37
Q

Dioxygenases adds hydroxyl groups to ____ or ____.

A

Proline or lysine

38
Q

Adding hydroxyl groups to proline or lysine for the …

A

formation of collagen molecule

39
Q

Dioxygenases are used in the biosynthesis of …

A

Carnitine

40
Q

What is carnitine is essential for?

A

Fatty acid transport into mitochondria

41
Q

Dioxygenases are used in the metabolism of?

A

Tyrosine

42
Q

What symptoms are related to the impaired function of these two families of enzymes?
* (Especially in impairment of collagen formation)

A

Scurvy symptoms

43
Q

Vitamin C acts as an antioxidant by preventing intracellular?

A

Protein oxidation

44
Q

The prevention of intracellular protein oxidation is relevant in which tissues with high oxidant production?

A
  • Neutrophils
  • Monocytes
  • Macrophages
45
Q

The prevention of intracellular protein oxidation is relevant in which tissues with high oxygen concentrations?

A
  • Lungs

- Tissues of the eye exposed to light

46
Q

Vitamin C acts as an antioxidant extracellularly by preventing?

A

Oxidant-mediated damage extracellularly

47
Q

Vitamin C prevents oxidant-mediated damage extracellularly by quenching … (2)

A
  • Aqueous peroxyl radicals

- Lipid peroxidation products (rancid fats)

48
Q

Vitamin C is preferentially used before what? (3)

A
  • Tocopherols (Vit. E)
  • Bilirubin
  • Uric acid
49
Q

Vitamin C affects several pathways involved in what?

A

Atherogenesis

50
Q

Vitamin C protects LDL from what?

A

Metal catalyzed oxidation

  • Hypothesized to be an initiating factor in atherogenesis
51
Q

Vitamin C can regenerate oxidized …

A

alpha - tocopherol (Vitamin E)

52
Q

Vitamin C affects several pathways involved in atherogenesis, and can decrease …

A

Lipid peroxidation

53
Q

Vitamin C can decrease adhesion of ______ to endothelium of vascular system?

A

Monocytes

54
Q

Vitamin C can decrease aggregation of ______ & _______.

A

Platelets and leukocytes

55
Q

Vitamin C can quench oxidants that ‘leak’ from activated ______ or ______, which prevents damage to supporting tissues such as collagen and surrounding fibroblasts.

A

Neutrophils or macrophages

56
Q

Vitamin C is involved in cholesterol degradation for …

A

Bile acid synthesis

57
Q

What retards cholesterol transformation into bile acids?

A

Vitamin C deficiency

58
Q

What has been implicated as a risk factor in CVD?

A

Hypovitaminosis C

59
Q

Vitamin C is involved in the conversion of folacin to

A

Tetrahydrofolate (THF)

60
Q

Vitamin C is involved in the synthesis of

A

adrenal tissue steroids (noradrenaline)

61
Q

Vitamin C helps iron absorption by …?

A
  • reducing ferric to ferrous form

- and is involved in transfer from plasma transferrin to liver ferritin

62
Q

Vitamin C improves immune response by increasing? (4)

A
  • Immunologic activity of leukocytes
  • Interferon production
  • Integrity of mucous membrane
  • Processes of inflammatory reactions
63
Q

What was found to be lower in HIV subjects?

A

Plasma ascorbate

64
Q

What treatment is commonly used in HIV subjects?

A

Interferon treatment

65
Q

Tolerable upper limit was set due to what at higher doses?

A

Gi adverse affects

66
Q

Who is at risk for deficiency? (3)

A
  • Smokers
  • Individuals with limited food variety
  • Females using oral contraceptives
67
Q

Smokers have lower ____ & _____ vitamin C levels, and require additional 35mg/day of vitamin C.

A

plasma & leukocyte

68
Q

What are the best sources of vitamin C?

A

Fruits and vegetables

69
Q

What are the earliest symptoms of scurvy?

A

Weakness & lassitude (a state of physical or mental weariness; lack of energy)

70
Q

A symptom of vitamin C deficiency results in an autoimmune disease in which sufferers experience dry mouth & dry eyes.

A

Sjogren’s Syndrome

71
Q

Ingestion of 3g of Vitamin C or more per day can cause what? (4)

A
  • Osmotic diarrhea
  • Bloating
  • Hyperuricosuria
  • Iron overload in certain cases
72
Q

Presence of excessive amounts of uric acid in urine, associated with kidney stones.

A

Hyperuricosuria

Metabolism II (7 decks)

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