Vitamin C

Question 1

Vitamin C (ascorbic acid) is not a vitamin for many animals because most animals have the ability to convert glucose to vitamin C. But man and other primates, bats, guinea pigs and some birds have lost ability to synthesize this vitamin. Why are we unable to synthesise vitamin C from glucose?

Answer 1

The dehydrogenation step is lacking due to absence of the enzyme L-gulonolactone oxidase.

Note:
~ Gulonic acid can be converted to a cyclic lactone, which in a two-step process involving dehydrogenation and enolization is converted to L-ascorbic acid (Vitamin C).

Question 2

State the dietary sources of vitamin C.

Answer 2

Lemons, citrus fruits, oranges, tangerines, vegetables

Question 3

State the role of vitamin C.

Answer 3

• Ascorbate is a major antioxidant, protecting cells and tissues from damage by free radicals, peroxides, and other metabolites of O2. It probably functions in cooperation with glutathione and α- tocopherol (vitamin E). [Remember that vitamin E prevents lipid membranes from oxidative attack and from peroxidation hence the reason].
• Vitamin C is required in the hydroxylation of proline and lysine residues to 4-hydroxyproline and hydroxylysine of procollagen which stabilizes fibers of newly synthesized collagen, a fibrous protein found in connective tissue and bone.
• Vitamin C is also required in synthesis of catecholamines and L-carnitine. [Catecholamines, such as dopamine, adrenaline (epinephrine), and noradrenaline, are hormones produced by the brain, nerve tissues, and adrenal glands. They play a key role in the body’s “fight-or-flight” response. L-carnitine is an amino acid derivative that plays a crucial role in the production of energy within the body. L-carnitine transports fatty acids into mitochondria.]

Question 4

Outline the deficiency effects of vitamin C.

Answer 4

• Lack of vitamin C causes scurvy. This is characterized by bleeding gums, sore mouth and hyperkeratosis (i.e thickening of the outer horny layer of the skin).
• A deficiency of vitamin C results in insufficient hydroxylation of collagen and the abnormal collagen fibers that as a result are unable to maintain normal tissue strength.
• Folate synthesis requires vitamin C for its synthesis hence lack of vitamin C leads to anemia.