6

Question 1

Vitamin C (Ascorbic Acid):
-The active forms are :
-Absorption
-Storage

Answer 1

1-L-ascorbic acid. 2-Dehydro-ascorbic acid.
Absorption: § From small intestine. Undergoes oxidation prior to absorption.
§ Co-transport across intestinal membrane (sodium dependent) & transported into blood
§ Storage: stored almost in all tissues in the
oxidized form, dehydro-ascorbic acid.

Question 2

Stability: many factors can lead to rapid degradation of vitamin C into less active species as:

Answer 2

light, temperature, enzymatic oxidation, atmospheric oxygen, metal ions, and alkaline pH

Question 3

Vitamin C Excretion

Answer 3

main metabolite is excreted by the kidney as an oxalate
salt. So, megadose for long time may cause kidney stones in addition to
diarrhea.

Question 4

Functions of Vitamin C:

Answer 4

1-main function is as a reducing agent in many tissues.
-involved in cellular oxidation-reduction reactions, may serve as a hydrogen transport agent.
Vitamin C facilitates the absorption of dietary iron from
the intestine by reducing Fe 3+ iron to the Fe2+ state.
2-Role in Collagen Synthesis:
-acts as a coenzyme in hydroxylation reactions of proline & lysine of procollagen to be converted to mature collagen fibers. requires also the presence of molecular O2& Fe2
-crosslinking of the helical proteins post- translationally.
-maintenance of normal connective tissue &wound healing.
3-Antioxidant Effect of Vitamin C:
4- Involved in tyrosine metabolism: epinephrine, norepinephrine, serotonin, dopamine.
5- Role in formation of carnitine, ferritin, FH 4.
6-Maturation of glial cells in developing nervous system.
7-Bile acid formation / cholesterol degradation.
8-Vasodilation & anticlotting [via activation of nitric oxide (NO release)].
9-Aids in prevention of cancers of oral cavity and pancreas.

Question 5

Vitamin C Deficiency

Answer 5

scurvy
characterized by sore and spongy gums, loose teeth,
fragile blood vessels, swollen joints, fatigue and a
microcytic anemia due to ↓ absorption of iron.

Question 6

Effects of Excess Vitamin C :

Answer 6

GI problems including abdominal pain & diarrhea.
§ ↑risk of kidney stones* in susceptible individuals. It is metabolized to
oxalate → ↑ oxalate excretion → calcium oxalate stone.

↑risk of iron toxicity in susceptible individuals, with disorders of iron
metabolism, as hemochromatosis, thalassemia,

Question 7

Thiamine (Vitamin B1)

Source, biologically active form

Answer 7

dried yeast, wheat germ, whole grains, whole brown rice, fish, lean meats & milk, cereals, fortified, or enriched grain products.

Thiamine pyrophosphate (TPP)

Question 8

TPP acts as a coenzyme in:

Answer 8

§ Formation or degradation of α-ketols by transketolase (Figure A).
§ Oxidative decarboxylation of α-keto acids as pyruvate to acetyl CoA by pyruvate dehydrogenase (Figure B).
§ In keto-dehydrogenase complex.

branched-chain α-keto acid dehydrogenase of muscle.

Question 9

Clinical Importance of Thiamine

Answer 9

The oxidative decarboxylation of pyruvate and α ketoglutarate, which plays a key role in energy metabolism of most cells, is particularly important in tissues of the CNS.

Question 10

Thiamin or Vitamin B1 Deficiency :

Answer 10

Beriberi severe thiamine-deficiency syndrome found
in areas where polished rice is the major component of
the diet. There are two forms:
§ Dry Beriberi (Neuropathy): symptoms include muscle
weakness & atrophy, confusion, nystagmus, paralysis &
encephalopathy in severe cases.
§ Wet Beriberi (Cardiopathy): tachycardia, vomiting, convulsions, edema, abnormal ECG & if not treated,
death (infants).

Question 11

Causes of Thiamin or Vitamin B1 Deficiency:

Answer 11

§ Insufficient intake (polished rice mainly used). § Alcoholism. § Dialysis. § Genetic disorder.

Question 12

Vitamin B 3 , Niacin or Nicotinic Acid:

Sources, synthesized in the……from

The active forms are

Answer 12

meat, liver, poultry, tuna, salmon, cereal, beans, seeds, milk,
green leafy vegetables, yeast, unrefined & enriched grains and cereals, milk. Coffee & tea.

synthesized in the liver from tryptophan

nicotinamide adenine dinucleotide (NAD+) and
nicotinamide adenine dinucleotide phosphate (NADP+).

Question 13

Vitamin B 3acts as a

Answer 13

coenzyme in the redox reaction About 200 enzymes require NAD or NADP as a coenzyme; act as hydrogen donors or acceptors.

Question 14

Vitamin B 3Deficiency:

Answer 14

§ Fatigue, lack of concentration, restless, anxiety,
irritability.
§ Severe cases results in “Pellagra”: initially it presents
as red scaly rash on sun-exposed areas. As the red rash
improves, it leaves behind a dark brownish red rash.
Sy mptoms are Called 4D’s:
§ Dermatitis, Diarrhea, Dementia & Death if untreated.

Question 15

Pantothenic Acid; Vitamin B5:

Function, Pantothenic Acid Deficiency:

Answer 15

required for synthesis of Coenzyme A
CoA performs a vital role by transporting acetyl
groups from one substrate to another.

found everywhere, so isolated deficiency is unlikely § Symptoms are: Muscle weakness, Paresthesia of the limbs and burning feet
syndrome.

Question 16

Vitamin B6 is a collective term of

Sources

Answer 16

Vitamin B6 is a collective term of pyridoxine,
pyridoxal & pyridoxamine.
meat, fish, legumes, dried yeast & whole grains.

Pyridoxine occurs primarily in plants, whereas
pyridoxal & pyridoxamine are found in foods
obtained from animals.

Question 17

Vitamin B6:
Function:

Answer 17

All 3 compounds are precursors of the biologically
active coenzyme, pyridoxal phosphate (PLP).

coenzyme for a large number of enzymes, particularly those that catalyze reactions involving amino acids metabolism

Question 18

Vitamin B6 Deficiency:

Answer 18

Symptoms are:
§ Seborrhea-like skin lesions
§ Anemia.
§ Neuropathy.
§ Convulsions.
§ Sleepiness, fatigue, glossitis, stomatitis.
§ In adults, may cause depression and confusion.

Question 19

Causes of Vitamin B6 Deficiency:

Answer 19

usually caused by pyridoxine-inactivating drugs

Dietary insufficiency:

Question 20

Pyridoxine; Vitamin B6 Toxicity:

Answer 20

Pyridoxine is the only water-soluble vitamin with significant toxicity.

Neurologic symptoms: sensory neuropathy,

Question 21

Riboflavin, Vitamin B2:

The active forms

Answer 21

flavin-mononucleotide (FMN) & flavin-adenine
dinucleotide (FAD).

Question 22

Vitamin B 2 acts as a
Functions of Riboflavin (Vitamin B2):

Answer 22

coenzyme in metabolism (involved in redox reactions )
§ Electron transport chain.
§ In succinate dehydrogenase (in TCA).
§ In fatty acyl dehydrogenase (in β-oxidation).
§ In metabolism of drugs or toxins.
§ As a coenzyme for: xanthine oxidase, aldehyde oxidase, pyridoxine
phosphate oxidase. § Synthesis of folate. § Monoamine oxidase metabolism: – a neurotransmitter.

Question 23

Vitamin B2 Deficiency, Riboflavin:

Answer 23

Isolated deficiency is rare. Mostly occurs in association
with other deficiencies.
Symptoms of riboflavinosis are:
§ Sore throat, stomatitis. § Glossitis, angular cheilitis. § Seborrheic dermatitis. § Corneal vascularization in some cases.