Nutrition Lecture 9: Riboflavin

Question 1

What are rich sources of riboflavin?

Answer 1

Main source = dairy products
Fortified sources: weet-bix, soy milk

Question 2

What is the structure of riboflavin?

Answer 2

Ribose sugar and Flavin structure

Question 3

What does riboflavin look like?

Answer 3

A yellow-orange crystalline solid

Question 4

What is riboflavin rapidly inactivated by?

Answer 4

UV and visible light

Question 5

What is the solubility of riboflavin?

Answer 5

Poor solubility in water compared to other B-vitamins

Question 6

What is the bioavailability of riboflavin?

Answer 6

High - 95% absorbed

Question 7

When does riboflavin absorption decline?

Answer 7

High doses > 27 mg

Question 8

Where is most riboflavin absorbed?

Answer 8

In proximal small intestine

Question 9

How is riboflavin absorbed into and out of enterocytes?

Answer 9

via riboflavin vitamin transporters (RFVT)

Question 10

How are high doses of riboflavin absorbed?

Answer 10

by passive diffusion

Question 11

How is riboflavin transported?

Answer 11

On proteins - primarily albumin

Question 12

Where is riboflavin stored?

Answer 12

Stored in only small amounts in the liver, heart and kidney - enough for 2-6 weeks

Question 13

What is the main function of riboflavin?

Answer 13

An integral component of flavocoenzymes

Question 14

What are flavocoenzymes?

Answer 14

a group of enzymes that contain flavin cofactors derived from riboflavin (vitamin B2)

Question 15

What are the flavocoenzymes that riboflavin are part of? (2)

Answer 15

FMN and FAD

Question 16

What does FMN stand for?

Answer 16

Flavin mononucleotide

Question 17

What does FAD stand for?

Answer 17

Flavin adenine dinucleotide

Question 18

What is the more common flavocoenzyme that riboflavin is converted into?

Answer 18

FMN = 60-90% of riboflavin in cells

Question 19

What is the less common flavocoenzyme that riboflavin is converted into?

Answer 19

FAD = 5-20% of riboflavin in cells

Question 20

What is the structure of Flavin mononucleotide (FMN)?

Answer 20

Riboflavin with an added phosphate group

Question 21

What is the structure of Flavin adenine dinucleotide?

Answer 21

Riboflavin with a phosphate group (FMN) and an AMP

Question 22

What is an AMP?

Answer 22

Adenosine and a monophosphate

Question 23

What are the three major roles of FMN and FAD?

Answer 23

1. Redox reactions
2. Antioxidant
3. Metabolism of B-vitamins

Question 24

What is OIL RIG?

Answer 24

Oxidation is Loss
Reduction is Gain
- of electrons

Question 25

Which flavocoenzyme is part of the ETC?

Answer 25

FMN

Question 26

What part of the ETC is FMN part of?

Answer 26

Complex 1 - it is able to take on board the high energy electrons from the NADH, 4 hydrogen ions are being pumped into the intermembrane space

Question 27

FMN is also important for some co-enzymes that metabolise...

Answer 27

drugs and toxins in the body

Question 28

What do antioxidants protect the body from?

Answer 28

Free radicals - molecules with an unpaired electron so highly unstable and reactive

Question 29

What do free radicals damage?

Answer 29

DNA, proteins and lipids

Question 30

What are two FAD-dependent enzymes?

Answer 30

1. Glutathione reductase 2. Xanthine oxidase

Question 31

What is the glutathione peroxidase assay?

Answer 31

test used to measure the activity of the enzyme glutathione peroxidase (GPx) in biological samples

Question 32

What B vitamins does Riboflavin help metabolise?

Answer 32

Folate, B6 and niacin

Question 33

How is riboflavin involved in folate metabolism?

Answer 33

MTHFR is an FAD-dependent enzyme which maintains the specific folate co-enzyme required to form methionine from homocysteine

Question 34

How is riboflavin involved in Vitamin B6 metabolism?

Answer 34

Conversion of most naturally available B6 to its coenzyme form, requires the FMN dependent enzyme PPO

Question 35

How is riboflavin involved in niacin metabolism?

Answer 35

Synthesis of niacin containing coenzymes, NAD and NADP requires a FAD-dependent enyme

Question 36

What are symptoms of riboflavin deficiency?

Answer 36

- Redness and swelling of mouth and throat - Cracks or sores on mouth - Inflammation of tongue - Dermatitis

Question 37

What are the risk factors for riboflavin deficiency?

Answer 37

- Alcoholism - No dairy intake - Poorly controlled hypothyroidism - Very physically active

Question 38

What is the EAR for riboflavin?

Answer 38

Men = 1.1mg/day Women = 0.9mg/day

Question 39

What is the RDI for riboflavin?

Answer 39

Men = 1.3mg/day Women = 1.1mg/day

Question 40

What is the upper level of riboflavin intake?

Answer 40

No upper level of intake set