UNIT 11: MICRONUTRIENTS III - Niacin, Riboflavin, Thiamin

Question 1

What are enzyme cofactors?

Answer 1

molecules that carry out biological roles

Question 2

What are 2 groups of enzyme cofactors?

Answer 2

• soluble cofactors: substrate in reaction

- prosthetic groups: pass functional groups between substrates and products

Question 3

NAD+ is a ___ while FAD is a ___

Answer 3

NAD+ soluble cofactor

FAD prosthetic group

Question 4

What is niacin?

Answer 4

aka vitamin B3

water soluble vitamin

Question 5

Nicotinic acid are in ____ and Nicotinamide are in _____

Answer 5

Nicotinic acid - plants

Nicotinamide - animals

Question 6

What are food sources of niacin?

Answer 6

fish, meats, breads, cereal, coffee (via heat)

Question 7

What is the source of niacin in the body?

Answer 7

Tryptophan –> niacin

in the liver

Question 8

NAD and NADP are which form of nicacin?

Answer 8

• in plants are nicotinic acid but converted to nicotinamide to form NAD and NADP

Question 9

How does nicotinic acid (the plant provitamin) form nicotinamide in vivo?

Answer 9

needs to be incorporated to NAD+ as nicotinamide

- nicotinic acid + tryptophan = nicotinamide

Question 10

What is the point of the P in NADP?

Answer 10

so enzymes can differentiate between NAD and NADP redox reactions
- specificity

Question 11

Which has a greater concentration:
NAD+ or NADH
NADP+ or NADPH

Answer 11

NAD+&raquo_space;>
NADPH&raquo_space;>

conc. differences encourages redox couples to be driven in the correct direction

Question 12

NAD+ plays a role in ribosylation via…

Answer 12

addition of a single or multiple ADP-ribose (from NAD+) to acceptor protein

single = mono(ADP)ribosylation - bacteria
multiple = poly(ADP) ribosylation) - DNA repair/replication/transcription

Question 13

What is Pellagra?

Answer 13

niacin Deficiency
4Ds
- Diarrhea
- Dermatitis
- Dementia
- Death

Question 14

What is riboflavin?

Answer 14

water soluble vitamin

Question 15

What are the dietary forms of riboflavin?

Answer 15

• free riboflavin
• flavin mononucleotide (FMN)
• flavin adenine dinucleotide (FAD)

Question 16

What are the redox couples that involve riboflavin?

Answer 16

FMN –> FMNH2
FAD –> FADH2
accept 2 e-

Question 17

What is the major form of riboflavin?

Answer 17

FMN (60-95%)

- production positively regulated by T3

Question 18

What is the most critical role of riboflavin as a cofactor?

Answer 18

• regenerate the reduced GSH by glutathione reductase

- NADPH passes e- to FAD for GSSG —> GSH

Question 19

What is thiamin?

Answer 19

water soluble vitamin

Question 20

Thiamin is found as ___ in plants and ___ in animals

Answer 20

Free thiamin - plants

TPP (Thiamin pyrophosphate) - animals

Question 21

Pyruvate dehydrogenase and a-ketoglutarate require _____ enzyme cofactor

Answer 21

thiamin

Question 22

How is thiamin involved with pyruvate dehydrogenase (PDC) reaction? Which other enzymes are involved?

Answer 22

1. decarboxylase
   thiamin as TPP is attached to PDC
   - TPP attacks carbonyl carbon of pyruvate to release CO2
2. Transacetylase
   - addition of CoA
3. Dehydrogenase
   - uses FAD –> FADH as prosthetic group to transfer 2e- to NAD+ –> NADH (e- carrier)

Question 23

Thiamin is required as an enzyme cofactor for pyruvate dehydrogenase and a-ketoglutarate dehydrogenase. What other pathways is it used in?

Answer 23

transketolase pathway
- PPP and HMPS

nerve transmission (TPP)

Question 24

What is BeriBeri?

Answer 24

Thiamin deficiency

Question 25

What are 3 forms of Beriberi?

Answer 25

• infantile (infants extreme sensitivity to thiamin sensitivity)
• wet (children and youth)
• dry (older adults)