Vitamin C - Ascorbic acid

Question 1

absorption of vit C

Answer 1

glucose is passively absorbed into liver to be synth. into ascorbic acid there
(active glucose tp. in humans, primates and guniea pigs)

Question 2

excretion

Answer 2

oxidised form in kidney, in urine (dehydroascorbic acid)

Question 3

where is ascorbic synthesized

Answer 3

in liver except in birds: kidney

Question 4

what are the biochemical roles of vitamin C

Answer 4

1. hydroxylation
2. H-donor
3. electron donator
4. antioxidant

Question 5

hydroxylation activity of vit. C

- H- donator, reducing agent

Answer 5

• OH-pro/OH-Lys: needed in collagen synthesis
• steroid hormone synthesis: steroid hydroxylase (stress hormones)
• bile acid synthesis
• Trp -> OH-Trp -> serotonin
• Tyr degradation -> Tyr -> OH-tyr -> DOPA (stress)

Question 6

H-donor activity of vit. C

Answer 6

FH2 reductase

- FH2->FH4

Question 7

electron donator activity of vit. C

Answer 7

reducing agent: Fe³⁺ –> Fe²⁺ –> intestinal absorption for heme synthesis

Question 8

antioxidant activity of vit. C

Answer 8

H2O2 -> 2H2O (H-donator)

Question 9

role in steroid hormone synthesis

Answer 9

• role in various OH-enzymes in initial stage of hormonal synthesis
• from corticosteroid synthesis in mitochondrium: e.g. corticol, steroid OH-enzymes in adrenal gland

Question 10

deficiency: collagen synthesis

Answer 10

• scurvy disease: decrease OH-pro/Lys decreases collagen synthesis -> bleeding gums, vessel rupture/damage, less osteoid -> weak bone
• after burning skin: vitC needed to provide skin collagen!

Question 11

deficiency: stress

Answer 11

heat stress in poultry and swine decreases hormone synthesis of ascorbic acid, as the glucose is used for incr. the blood glucose conc.

Question 12

deficiency: anaemia

Answer 12

less Fe²⁺ -> less intestinal absorption of iron to produce hb
- less FH4 synthesis, as it needs vit. C to function, decr. DNA synthesis