B3 Niacin

Question 1

What B vitamin functions as a coenzyme as NADP/NADPH?

Answer 1

Niacin

Question 2

List the metabolic roles of NADPH.

Answer 2

NADPH is used in biosynthesis reactions

1. fatty acid synthesis
2. cholesterol and steroid hormone synthesis
3. synthesis of deoxyribonucleotides
4. oxidation of glutamate

In regeneration of antioxidants

5. regeneration of glutathione
6. regeneration of vitamin C
7. regeneration of thioredoxin

Vitamin metabolism
8. folate metabolism (several reactions dependent on NADPH).

nicotinamide is a derivative of niacin and is used by the body to form the coenzymes NAD (nicotinamide adenine dinucleotide) and NADP (nicotinamide adenine dinucleotide phosphate). Approx 300 enzymes require NAD or NADP.

NADP functions most often in biosynthetic (anabolic) reactions. NADP is round in cells mainlyin its reduced form NADPH.
(NAD functions most often in degredation (catabolism) of carbohydrates, fats, proteins and alcohol. NAD is found primarily in its oxidized form NAD)

NAPDH is generated from NADP by reduction in the pentose phosphate pathway

Question 3

Which amino acid is a precursor to niacin?

Answer 3

tryptophan

Question 4

List the effects of niacin toxicity on the body.

Answer 4

Effects of niacin toxicity in the body include:

1. flushing and redness along with burning, itching, tingling and headaches (vasodilatory effects)
2. gastrointestinal problems such as heartburn, nausea and vomiting
3. livery injury
4. hyperuricemia and gout
5. elevation of plasma glucose concentrations

Question 5

True or False: Increased blood pressure is a sign of Niacin toxicity?

Answer 5

False

increased blood pressure

niacin causes vasodilation (so would not increase blood pressure)

Question 6

Quiz ?: Large doese of vitamin B3 as nicotinamide (nicinamide) do not possess the hypocholesterolemic effects of nicotinic acid (niacin), but also do not appear to have as high a potential for toxicity? True or False?

Answer 6

True

Question 7

Which B vitamins are necessary in the pyruvate dehydrogenase complex?

Answer 7

thiamin (TPP)
riboflavin (FAD)
niacin (NAD)
pantothentic acid (CoA-SH)

pyruvate dehydrogenase is a multicomplex enzyme that catalyzes the conversion of pyruvate to acetyl CoA so it can enter the TCA cycle

Question 8

What are the forms of niacin?

Answer 8

Nicotinic acid

Nicotinomide

Bound forms

Question 9

How many mg of tryptophan are equal to 1 niacin equivalent?

Answer 9

60 mg tryptophan is equal to 1 niacin equivalent.

To get 60 mg of tryptophan you would need to consume 10 g of complete protein
(Every 1 g of complete protein provides 10 mg of tryptophan)

Question 10

In the IS diet what % of niacin intake comes from tryptophan conversion?

Answer 10

About 50%

Question 11

What reactions require NAD?

Answer 11

Oxidative reactions where NAD is converted to NADH

1. Glycolysis
2. Oxidative decarboxylation of pyruvate to generate acetyl coA
3. TCA cycle
4. Beta-oxidation of fatty acids

Question 12

What reactions require NADPH?

Answer 12

NADPH is used in biosynthetic reactions

1. Fatty acid synthesis
2. Cholesterol and steroid hormone synthesis
3. Proline symthesis
4. Regeneration of antioxidants
   - glutathione
   - vitamin C
   - thioredoxin
5. Synthesis of folate coenzymes
6. Deoxyribonucleotide synthesis (DNA precursor)