Micronutrients (Water soluble vitamins)

Question 1

What is the common functional role of water-soluble vitamins in cells?

Answer 1

They function as cofactors and coenzymes in metabolic reactions.

Question 2

What is the active coenzyme form of thiamin, and what is its role?

Answer 2

Thiamine pyrophosphate (TPP); it acts as a cofactor in decarboxylation (e.g., pyruvate → acetyl-CoA) and transketolation reactions (Pentose Phosphate Pathway).

Question 2

What are the deficiency diseases of thiamin?

Answer 2

Beriberi (Wet: cardiovascular; Dry: neurological).

Wernicke-Korsakoff syndrome (ataxia, confusion; common in alcoholism).

Question 2

List the water-soluble vitamins.

Answer 2

Thiamin (B1), Riboflavin (B2), Niacin (B3), Pantothenic acid (B5), Pyridoxine (B6), Biotin (B7), Folic acid (B9), Cyanocobalamin (B12), and Vitamin C.

Question 2

How does alcoholism lead to thiamin deficiency?

Answer 2

lcohol reduces intake, impairs absorption, alters phosphorylation, and increases excretion of thiamin.

Question 2

What are the two coenzyme forms of riboflavin?

Answer 2

FMN (Flavin Mono Nucleotide) and FAD (Flavin Adenine Dinucleotide).

Question 2

What are the symptoms of riboflavin deficiency?

Answer 2

Glossitis (magenta-red tongue).

Angular stomatitis/cheilosis (mouth cracks).

Corneal vascularization and photophobia.

Question 2

What are the coenzyme forms of niacin?

Answer 2

NAD+ (catabolic reactions) and NADP+ (anabolic reactions, e.g., fatty acid synthesis).

Question 2

How can niacin be synthesized in the body?

Answer 2

From tryptophan (60 mg tryptophan → 1 mg niacin) via enzymes IDO and KAT.

Question 2

How is riboflavin deficiency diagnosed?

Answer 2

Measure urinary riboflavin or serum/erythrocyte levels (low levels confirm deficiency).

Question 2

What is the deficiency disease of niacin, and what are its symptoms?

Answer 2

Pellagra (“3 Ds”): Dermatitis (glove-like rash), Diarrhea, Dementia.

Question 2

What is the active form of pantothenic acid, and its primary function?

Answer 2

Coenzyme A (CoA); carries acyl groups (e.g., acetyl-CoA for Krebs cycle).

Question 2

Why is pantothenic acid deficiency rare?

Answer 2

It is synthesized by gut bacteria and widely available in foods.

Question 2

What is the active form of vitamin B6, and its key roles?

Answer 2

Pyridoxal phosphate (PLP); involved in:

Amino acid metabolism (transamination, decarboxylation).

Glycogenolysis (glycogen phosphorylase cofactor).

Question 2

What is biotin’s role in metabolism?

Answer 2

Coenzyme for carboxylation reactions (e.g., acetyl-CoA carboxylase).

Question 2

What causes B6 deficiency, and how is it treated?

Answer 2

Causes: Alcoholism, isoniazid use. Treatment: Oral pyridoxine (50–100 mg/day).

Question 2

What are the two active forms of B12, and their functions?

Answer 2

Methylcobalamin: Converts homocysteine → methionine.

Deoxyadenosylcobalamin: Converts methylmalonyl-CoA → succinyl-CoA.

Question 3

What is the active form of folate, and its key function?

Answer 3

etrahydrofolate (THF); donates one-carbon units for DNA synthesis and homocysteine → methionine conversion.

Question 3

What causes biotin deficiency?

Answer 3

Consumption of raw eggs (avidin binds biotin) or dialysis.

Question 3

What are the consequences of folate deficiency?

Answer 3

Macrocytic anemia (large RBCs due to impaired DNA synthesis).

Neural tube defects in fetuses.

Question 4

How does B12 deficiency present?

Answer 4

Megaloblastic anemia and neurological symptoms (e.g., subacute combined degeneration of spinal cord).

Question 5

What are the key functions of vitamin C?

Answer 5

Collagen synthesis (hydroxylation of proline/lysine).

Antioxidant and iron absorption (keeps iron as Fe²⁺).

Question 6

What is the deficiency disease of vitamin C?

Answer 6

Scurvy (symptoms: bleeding gums, poor wound healing, anemia).

Question 7

Why is thiamine given to alcoholics in medical settings?

Answer 7

To prevent Wernicke-Korsakoff syndrome (neurotoxicity from thiamine deficiency).

Question 8

What drug interferes with B6, and how is it managed?

Answer 8

Isoniazid (TB drug); give pyridoxine supplements (30–50 mg/day).

Question 9

Which two critical enzyme complexes require TPP (thiamine pyrophosphate)?

Answer 9

Pyruvate dehydrogenase complex (converts pyruvate → acetyl-CoA). Transketolase (in the Pentose Phosphate Pathway).

Question 10

Why is riboflavin called the "luminescent vitamin"?

Answer 10

It fluoresces under UV light and is destroyed by light exposure (e.g., milk in clear bottles).

Question 11

How does riboflavin link to energy production?

Answer 11

As FAD/FMN, it carries electrons in the ETC (NAD → FMN → CoQ → Cytochromes).

Question 12

Why does nicotinic acid (not nicotinamide) cause flushing?

Answer 12

It activates prostaglandin release (vasodilation). Used clinically to lower LDL.

Question 13

What rare disorders mimic niacin deficiency?

Answer 13

Hartnup disease (impaired tryptophan absorption). Carcinoid syndrome (tryptophan diverted to serotonin).

Question 14

Name 4 key CoA derivatives and their roles.

Answer 14

Acetyl-CoA (Krebs cycle, acetylcholine synthesis). Succinyl-CoA (heme synthesis). HMG-CoA (cholesterol synthesis). Acyl-CoA (fatty acid oxidation).

Question 15

Why is B5 deficiency rare?

Answer 15

Gut bacteria synthesize it, and it’s ubiquitous in foods.

Question 16

How does isoniazid cause B6 deficiency?

Answer 16

It inactivates pyridoxal phosphate (PLP) by binding to it, blocking coenzyme function.

Question 17

Which neurological symptoms occur in B6 deficiency?

Answer 17

Peripheral neuropathy, seizures (PLP needed for GABA synthesis).

Question 18

Why do raw eggs cause biotin deficiency?

Answer 18

Avidin in egg whites tightly binds biotin, preventing absorption.

Question 19

What is the classic rash of biotin deficiency called?

Answer 19

Biotin-deficient face" (scaly dermatitis, alopecia, "hair and skin" = Haar und Haut).

Question 20

Why does B12 deficiency cause functional folate deficiency?

Answer 20

B12 is required to regenerate active THF from methyl-THF ("folate trap").

Question 21

Which drugs inhibit folate metabolism?

Answer 21

Methotrexate (DHFR inhibitor). Valproic acid (impairs absorption; linked to neural tube defects).

Question 22

Why does B12 deficiency elevate methylmalonic acid (MMA)?

Answer 22

Deoxyadenosylcobalamin is needed to convert methylmalonyl-CoA → succinyl-CoA.

Question 23

What lab findings distinguish B12 vs. folate deficiency?

Answer 23

Both: Macrocytic anemia, high homocysteine. Only B12: High MMA, neurological symptoms.

Question 24

How does vitamin C deficiency cause poor wound healing?

Answer 24

It’s required for proline hydroxylation in collagen, stabilizing triple-helix structure.

Question 25

Why does vitamin C enhance iron absorption?

Answer 25

It reduces dietary Fe³⁺ → Fe²⁺, the absorbable form.

Question 26

A patient with chronic alcoholism has confusion and ataxia. What’s the immediate treatment?

Answer 26

IV thiamine (200 mg) to prevent Wernicke encephalopathy.

Question 27

A pregnant woman takes valproic acid for epilepsy. What vitamin deficiency is she at risk for?

Answer 27

Folate (valproic acid impairs absorption; increases neural tube defect risk).

Question 28

Which B vitamins are cofactors for these enzymes?

Answer 28

Pyruvate dehydrogenase → TPP (B1). Methionine synthase → B12. Glycogen phosphorylase → PLP (B6).

Question 29

Why are breastfed infants at risk for thiamine deficiency?

Answer 29

: If the mother is deficient (e.g., malnutrition), infantile beriberi occurs (hoarseness, edema).

Question 30

Which vitamin deficiency is common in dialysis patients?

Answer 30

Biotin (lost during dialysis).