VITAMIN B3 and VITAMIN B2

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Ha Thi Thuy Hoa
K15 Honor Program
of Biology
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OUTLINE
I. Introduction
II. Vitamin B3: Nicotinic acid and Vitamin B3-
the nicotinamide coenzymes : NAD+ and
NADP+
III. Vitamin B2: Riboflavin and the Flavin
Coenzymes FAD, FMN
IV. Summary and Question

I. INTRODUCTION
What is the most important function of Vitamin B ?
Why do we need vitamin B everyday?

Play important roles
in cell metabolism.
= They are
coenzymes for
carrying hydrogens and
their electrons during
metabolic reactions
II.Nictotinic acid
Nicotinamide adenine dinucleotide (phosphate)
NAD NADP
Reaction of NAD
Differences between NAD/NADH
and NADP/NADPH

In many cells and tissues, the ratio NAD/NADH is high,
therefore favoring hydride transfer from a substrate to NAD to
form NADH.
->Role: NAD generally functions in oxidations – a part of
catabolic reaction.(oxidation such as pyruvate in the
mitochondrial matrix)

By contrast, NADPH is generally at a higher concetration than
NADP, favoring hydride transfer from NADPH to substrate.
->Role: NADPH is the usual coenzyme in reduction – as part of

an anabolic reaction (synthesis fatty acid in the cytosol)
Deficiency : Pellagra disease
III.Riboflavin
Flavin adenine dinucleotide (FAD)
Flavin
mononucleotide (FMN)
Flavoprotein

Flavoprotein are enzymes that catalyze oxidation-
reduction reactions using either FMN or FAD as
coenzymes.

FMN and FAD bind tightly to proteins such as
succinate dehydrogenase(in Krebs cycle). They do
not transfer electrons by diffusing from one enzymes
to another.

Under the reversible reduction, accepting either one
or two electrons in the form of one or two hydrogen
atoms from a reduced substrate.

The fully reduced form : FADH2 and FMNH2
Reaction of Riboflavin
Function of flavoproteins

Electrons carriers in oxidative phosphorylation (in
mitochondria)

Serve as light receptors in cryptochromes in chloroplast in
plant.

DIET OF VITAMIN B3
DIET OF VITAMIN B2
IV. QUESTIONS AND CONCLUSION

1. How many electrons NAD and FAD can carry?
Answer: NADH can transfer 2 electrons and 1 proton
while FAD can accept or donate electrons 1 or 2 at a time
and also 1 or 2 protons.

2. What is flavoprotein?
Answer: Flavoprotein are enzymes that catalyze
oxidation-reduction reactions using either FMN or FAD
as coenzymes. FMN and FAD bind tightly to proteins.
references

Text books: 1. Hoa Sinh hoc, Pham Thi Tran Chau, Tran
Thi Ang. 2. Principle of Biochemistry, Lehninger.

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
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http://
en.wikipedia.org/wiki/Nicotinamide_adenine_dinucleoti
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THANKS FOR YOUR ATTENTION
Figure 7.4

Coenzyme Action
©2003 Wadsworth, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.