Ascorbic Acid (Vitamin C)

Question 1

What are the two forms of vitamin C and which is active?

Answer 1

Dehydroascorbic acid is found in food

Must be reduced to ascorbic acid to be in active form

Question 2

How is ascorbic acid absorbed?

Answer 2

In small intestine

• dehydroascorbic acid: facilitated diffusion
• ascorbic acid: active transport

Best absorbed in small doses, larger doses = less absorption

Question 3

How is vitamin C transported through the body?

Answer 3

free in the blood as ascorbic acid

Question 4

Where is Vitamin C stored?

Answer 4

Not in a particular organ, is in body ‘pool’ of 300-400mg

Question 5

What is the function of Vitamin C?

Answer 5

• electron donor to free radicals (reducing agent)
• cofactor to metalloenzymes (e.g. glutathione peroxidase)
  this is bc when metalloenzymes are used the metal ion is often oxidised and ascorbic acid reduces it back to be reused
• Collagen synthesis

Question 6

Explain the role of vitamin C in collagen synthesis?

Answer 6

For strong collagen, the 3 protein strands need to form a tight triple helix

For this proline and lysine need to be hydroxylated (by prolylhyroxylase and lysinehydroxylase). These are metalloenzymes which require Fe3+ ion

This hydroxylation allows the twisting and binding into the helix structure

Ascorbic acid reduces iron to keep it in the Fe2+ form so that the enzymes can continue

Question 7

What is caused by an ascorbic acid deficiency?

Answer 7

• Scurvy (inadequate collagen synthesis, bleeding gums, poor wound healing, fatigue)

Question 8

What are sources of Vitamin C?

Answer 8

• Capsicum
• Kiwi
• Guava
• Strawberries