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IHN: Biochemistry 2 > Vitamin C > Flashcards

Vitamin C Flashcards

1
Q

vitamin C aka

A

ascorbic acid or ascorbate

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2
Q

ascorbic acid (ascorbate) is synthesize from __ by many animals in __ or __

A

ascorbic acid (ascorbate) is synthesize from glucose by many animals in liver or kidney

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3
Q

is ascorbic acid produced by humans?

A

NO

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4
Q

2 food forms of vit C present in foods

A

ascorbic acid (AA)
dehydroascorbic acid (DHA)

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5
Q

best sources of vit c

A

fruits and veggies

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6
Q

other sources of vit c

A

animal organs (liver, kidney, brains)

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7
Q

__% AA, __% DHA

A

80-90% AA, 10-20% DHA

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8
Q

common sources of vit C

A

camu berry
tomato
peppers

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9
Q

tolerable upper limit (UL) is __ based on adverse effects of __

A

tolerable upper limit (UL) is 2 g/day based on adverse effects of osmotic diarrhea

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10
Q

can you reach UL from dietary vit C alone

A

no, it is only caused by excess supplementatin

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11
Q

excess vitamin c cause increased excretion of __ and __ which may increase __ formation

A

excess vitamin c cause increased excretion of oxalate and uric acid which may increase kidney stone formation

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12
Q

contraindications: people with __, __ anemia, or __ should aboid ascorbate supplements

A

contraindications: people with hemochromatosis, sideroblastic anemia (heme deficiency even with adequate iron), or thalassemia major (excess iron) should aboid ascorbate supplements

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13
Q

ascorbic acid acts as an __ (__ agent) and reacts with __

A

ascorbic acid acts as an electron donor (reducing agent) and reacts with oxidants

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14
Q

ascorbic acid can donate __ electrons
its free radical form is __

A

ascorbic acid can donate 2 electrons
its free radical form is stable

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15
Q

where is vit c absorbed

A

ileum and jejunum

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16
Q

2 methods of vit C absorption (overviews)

A
  1. ascorbate is coupled to sodium and transported directly by SVCT (sodium-dependent vit C transporter)
  2. GLUT requires extracellular oxidation of ascorbate to DHA
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17
Q

SVCT mechanism

A
  1. ascorbic acid goes through SVCT with NA+ and enters cell (against the gradient)
  2. Na+ leaves through ATPase
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18
Q

SVCT type of transporter

A

symporter: secondary active

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19
Q

why use SVCT and waste ATP

A

bc ascorbic acid is scarce in nature, so we must take advantage of it when available

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20
Q

vit C GLUT transport mechanism

A
  1. Asc –> DHA
  2. DHA is similar to glucose –> goes through GLUT into enterocyte
  3. enterocyte produces Asc
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21
Q

GLUT type of transport

A

facilitated diffusion

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22
Q

GLUT 1, 2, and 3 regulation

A

glucose
competitive inhibition

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23
Q

GLUT 4 regulation

A

insulin sitmulates

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24
Q

GLUT 1, 2, 3 location

A

osteoblasts
muscle
intestinal cells

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25
Q

GLUT 4 location

A

adipose
muscle cells

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26
Q

SVCT1 location

A

liver epithelial
intestine
kidney

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27
Q

SVCT 1 regulation

A

ascorbate: feedback inhibition of SVCT expression
more ascorbate absorbed, less activity of SVCT

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28
Q

SVCT2 location

A

broad distribution (brain, retinal, and placenta cells)

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29
Q

SVCT1 knockout

A

total loss of ascorbate resorption in kidneys BUT intestinal absorption is unchanged

30
Q

SVCT2 knock out

A

severe ascorbate deficiency in tissues
KO IS LETHAL
mice die at birth

31
Q

__ transporters must exist, but remain unidentified

A

efflux transporters must exist, but remain unidentified

32
Q

as more ascorbate is absorbed, __ has __ activity
__ feedback

A

as more ascorbate is absorbed, SVCT1 has less activity
negative feedback

33
Q

resorption of ascorbate in renal tubules by SVCT1 carrier is __

A

resorption of ascorbate in renal tubules by SVCT1 carrier is saturable

34
Q

at vit C intakes of above __mg, all vit C is usually __

A

at vit C intakes of above 500 mg, all vit C is usually excreted

35
Q

ascorbate in blood is __ soluble and free in __

A

ascorbate in blood is water soluble and free in plasma

36
Q

tissue concentrations of ascorbate are __ than plasma levels
SO, ascorbate is actively transported __ a gradient into cells via a transporter

A

tissue concentrations of ascorbate are way higher than plasma levels
SO, ascorbate is actively transported against a gradient into cells via a transporter

37
Q

white blood cells have a concentration of ascorbate that is up to __ times __ than plasma

A

white blood cells have a concentration of ascorbate that is up to 80 times higher than plasma

38
Q

RBC and WBC uptake (via GLUT1 and GLUT3) and transport __ in circulation

A

RBC and WBC uptake (via GLUT1 and GLUT3) and transport DHA in circulation

39
Q

degradative oxidation of ascorbate occurs primarily in __ but also to some extent in __

A

degradative oxidation of ascorbate occurs primarily in liver but also to some extent in kidneys

40
Q

oxalic acid is found mainly in

A

spinach, but also lots of other foods

41
Q

oxalic acid acts as a magnet for __ molecules (like __)

A

oxalic acid acts as a magnet for positively charged molecules (like Ca, Fe, Zn)

42
Q

degradation: vit C is __ to DHA, then destroyed by __

A

degradation: vit C is oxidized to DHA, then destroyed by opening the ring

43
Q

ascorbate enzymatic role

A

reducing agent, iron and copper containing enzymes

44
Q

ascorbate non-enzymatic role

A

anti-oxidant and, possibly, pro-oxidant (by reducing free Fe and Cu ions)

45
Q

2 non-enzymatic mechanisms of ascorbate

A
  1. antioxidant (free radical quenching)
  2. potential functions (pro-oxidant, ROS formation)
46
Q

enzymatic mehcanisms of ascorbate (6)

A
  1. collagen synthesis (structural)
  2. carnitine synthesis (metabolic energy)
  3. catecholamine synthesis (hormonal)
  4. peptide amidation (ie vasopressin)
  5. epigenetic regulation (DNA and histone methylation)
  6. transcriptional regulation (ie HIF)
47
Q

ascorbate in collagen synthesis role:

A

ascorbate reduces heme iron (ferric –> ferrous)
this restores enzyme activity

48
Q

what enzyme activity is restored by ascorbate in collagen synthesis

A

prolyl hydroxylase

49
Q

in collagen synthesis, ascorbate __ iron3+ to __

A

in collagen synthesis, ascorbate reduces iron3+ to iron2+

50
Q

vit C is essential for __ synthesis

A

vit C is essential for carnitine synthesis

51
Q

carnitine can be acquired from __ or synthesized from __ and __

A

carnitine can be acquired from diet or synthesized from lysine and methionine

52
Q

ascorbate’s role in __ synthesis explains the first sign of vit C deficiency: __

A

ascorbate’s role in carnitine synthesis explains the first sign of vit C deficiency: fatigue

53
Q

scurvy is associated with high circulating levels of __ and excretion of high levels of __

A

scurvy is associated with high circulating levels of tyrosine and excretion of high levels of 4-hydroxyphenyl pruvate

54
Q

premature infants also have high levels of __ and excretion of high levels of __
__ fixes this issue

A

premature infants also have high levels of tyrosine and excretion of high levels of 4-hydroxyphenyl pruvate
ascorbate fixes this issue

55
Q

alkaptonuria is a mutation that inactivates __
this causes __ to accumulate in __ and turn it __ color

A

alkaptonuria is a mutation that inactivates homogentisate dioxygenase
this causes homogentisate to accumulate in urine and turn it black color

56
Q

depleted ascorbate prevents us from making __ and __

A

depleted ascorbate prevents us from making catecholamines and dopamine

57
Q

epinephrine and norepinephrine are synthesized in __ and __
synthesis occurs in __ compartments

A

epinephrine and norepinephrine are synthesized in neurons and adrenal gland
synthesis occurs in vesicular compartments

58
Q

what is needed to convert norepinephrine to epinephrine?

59
Q

ascorbate plays a role in hormone activation via

A

alpha-amidation

60
Q

alpha-amidation is essential in __ activation

A

alpha-amidation is essential in hormone activation

61
Q

hormone activation: ascorbate provides electrons in __ dependent mechanism

A

hormone activation: ascorbate provides electrons in cytochrome b-561 dependent mechanism

62
Q

vitamin c reduces several oxygen-centered __ and __

A

vitamin c reduces several oxygen-centered radicals and reactive species

63
Q

vit C is an antioxidant due to the __ power of __

A

vit C is an antioxidant due to the reducing power of ascorbate

64
Q

antioxidant function of ascorbate (3 things work together)

A

glutathione + Vit C + Vit E

65
Q

assessment of vit C, best method

A

WBC content of vit C

66
Q

assessment of vitamin C problems

A

no functional measure other than scurvy

67
Q

vitamin C deficiency and symptoms

A

scurvy
4 Hs
hemorrhage
hyperkeratosis
hypochondriasis
hematologic abnormalities

68
Q

earliest manifestations of scurvy are

A

dermatologic

69
Q

some early signs of scurvy are

A

unspecific
decreased appetite, fatigure, weakness

70
Q

groups at risk

A

malnourished ppl:
1. cancer cachexia
2. low SES
3. drug and alcohol
4. elderly men
5. children
6. keto diet (no fresh fruits or veggies)

71
Q

3 vitamin c controversial treatments (aka it does not work as a treatment)

A

CVD
cancer
common cold

IHN: Biochemistry 2 (38 decks)

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