1. Dental Biochemistry 2 – (Lec. 7)
Water soluble vitamins
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2. ASCORBIC ACID (VITAMIN C)
1. Chemistry of Vitamin C
• It is water soluble and is easily destroyed by heat,
alkali and storage. In the process of cooking, 70%
of vitamin C is lost. The structural formula of
ascorbic acid closely resembles that of
carbohydrates.
• It has strong reducing property
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3. 2. Biosynthesis of Ascorbic Acid in Animals
• Most animals and plants can synthesize ascorbic acid from
glucose. Man cannot synthesize ascorbic acid.
3. Excretion of Ascorbic Acid
• The vitamin is excreted in urine, Since vitamin C is
a strong reducing agent, the Benedict's test will be
positive in the urine sample after the vitamin
administration.
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4. 4. Biochemical Functions of
Vitamin C
• i. Hydroxylation of proline: Ascorbic acid is
necessary for the post-translational hydroxylation
of proline and lysine residues. Hydroxyproline
and hydroxylysine are essential for the formation
of cross-linkings in collagen, which gives the
tensile strength of the fibers. This process is
absolutely necessary for the normal production
of supporting tissues such as osteoid, collagen
and intercellular cement substance of capillaries.
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5. • ii. Iron metabolism: Ascorbic acid enhances
the iron absorption from the intestine. Ascorbic
acid reduces ferric iron to ferrous state, which is
preferentially absorbed.
• iii. Hemoglobin metabolism: It is useful for
reconversion of met-hemoglobin to hemoglobin.
• iv. Antioxidant property: As an antioxidant, it
may prevent cancer formation.
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6. 5. Dietary Sources of Vitamin C
• Rich sources are lime, lemon and green leafy
vegetables.
6. Requirement of Vitamin C
• Recommended daily allowance (RDA) is 75 mg/day
(equal to 50 ml orange juice). During pregnancy,
• lactation, and in aged people requirement may be
100 mg/day.
7. Therapeutic Use of Vitamin C
• Vitamin C has been recommended for treatment of
ulcer, trauma, and burns. 6

7. B COMPLEX GROUP OF VITAMINS
These vitamins are chemically not related to
one another. They are grouped together
because all of them function in the cells as
coenzymes.
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8. 1- THIAMINE (VITAMIN B1)
• Thiamine is also called as vitamin B1.
1.Sources
• Cereals (whole wheat flour and unpolished rice)
are rich sources of thiamine. When the grains are
polished, aleurone layer is usually removed. Yeast
is also a very good source.
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9. 1. Physiological Role of Thiamine
i. pyruvate dehydrogenase: The coenzyme form is
thiamine pyrophosphate (TPP). It is used in oxidative
decarboxylation of alpha keto acids, e.g pyruvate
decarboxylase, a component of the pyruvate
dehydrogenase complex. It catalyzes the breakdown of
pyruvate to acetyl-CoA, and carbon dioxide.
ii. Alpha Ketoglutarate dehydrogenase: An analogous
biochemical reaction that requires TPP is the oxidative
decarboxylation of alpha Ketoglutarate to succinyl CoA
and Co2 (TCA cycle).
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10. iii.Transketolase in the hexose mono-phosphate
shunt pathway of glucose.
The main role of thiamine (TPP) is in
carbohydrate metabolism. So, the requirement of
thiamine is increased along with higher intake of
carbohydrates thiamine. Also in case of
Polyneuritis that may be associated with
pregnancy and old age.
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11. • Recommended Daily allowance of thiamine
• It depends on calorie intake (0.5 mg/1000
calories).
• Requirement is 1-1.5 mg/day.
• Thiamine is useful in the treatment of beriberi,
alcoholic polyneuritis, neuritis of pregnancy and
neuritis of the old age.
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12. 2- RIBOFLAVIN (VITAMIN B2)
• 1. Structure of Riboflavin
• Riboflavin is converted to its active
coenzyme forms (FMN & FAD) with
the help of ATP.
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13. • 2. Coenzyme Activity of Riboflavin
• i. Riboflavin exists in tissues bound with
enzymes. Enzymes containing riboflavin are
called flavoproteins. The two coenzymes are
FMN (flavin mononucleotide) and FAD (flavin
adenine dinucleotide). The enzyme complex
contains molybdenum and iron also.
• ii. During the oxidation process, FAD accepts
two hydrogen atoms from substrate. In turn, FAD
is reduced to FADH2.
• iii. FADH2 when oxidized will generate 1.5 ATP
molecules. 13

14. Dietary Sources of Riboflavin
• Rich sources are liver, dried yeast, egg and whole
milk.
• Good sources are fish, whole cereals, legumes and green
leafy vegetables.
Daily Requirement
• Riboflavin is concerned mainly with energy metabolism
and requirement is related to calorie intake. Adults on
sedentary work require about 1.5 mg per day. During
pregnancy, lactation and old age, additional 0.2 to 0.4
mg/day are required.
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15. 3- NIACIN
• Niacin and Nicotinic acid are synonyms. It is
also called as pellagra.
• The term nicotinic acid is a vitamin; but,
nicotine is the potent poison from tobacco.
• Niacinamide is the active form of the vitamin,
present in tissues.
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16. 1.Chemistry of Niacin
• The coenzyme forms are Nicotinamide adenine
dinucleotide (NAD+) and Nicotinamide adenine
dinucleotide phosphate (NADP+)
• The nitrogen atom of niacinamide contains one
positive charge. The structure is abbreviated as
NAD+. (The +ve sign is always shown). In the
case of NADP+, one more phosphoric acid is
attached to the ribose of the AMP
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17. 2. One Hydrogen Atom and One
Electrons
i. In the oxidised form, nitrogen of the nicotinamide residue has a
hence the oxidized form of coenzyme is usually written as NAD+.
ii. In the process of reduction, NAD+ accepts one hydrogen atom fully.
The other hydrogen is ionized. Only the electron is accepted. See the
positive sign in the molecule is removed.
2H  H + H+ + e-
Thus, NAD+ accepts one H atom and one e- (electron), to form NADH.
The hydrogen ion (H+) is released into the surrounding medium. During
the oxidation of NADH, the reaction is reversed.
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18. 3. NAD+ Dependent Enzymes
• One NADH molecule is oxidized in the
respiratory chain to generates 2.5 ATPs.
4. NADPH Reactions
• NADPH is not used for ATP synthesis; it is
almost exclusively used for the reductive
biosynthesis.
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19. 6. Dietary Sources of Niacin
• The richest natural sources of niacin are dried yeast, rice
polishing, liver, peanut, whole cereals, legumes, meat and
fish. About half of the requirement is met by the
conversion of tryptophan to niacin. About 60 mg of
tryptophan will yield 1 mg of niacin.
9. Recommended Daily Allowance (RDA)
• Normal requirement is 20 mg/day. During lactation,
additional 5 mg are required.
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20. 4- VITAMIN B6
1. Coenzyme form
• Vitamin B6 is the term applied to a family of 3 related
pyridine derivatives; pyridoxine (alcohol), pyridoxal
(aldehyde) and pyridoxamine.
• Active form of pyridoxine is pyridoxal phosphate
(PLP). It is synthesized by pyridoxal kinase, ultilizing
ATP.
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21. 2. Functions of Pyridoxal phosphate
The pyridoxal phosphate (PLP) acts as coenzyme for many reactions
in amino acid metabolism.
I. Transamination: These reactions are catalyzed by amino
transferases (transaminases) which employ PLP as the coenzyme
• For example, alanine amino transferase
Alanine + Alpha keto glutarate  Pyruvate + Glutamic acid
II. Decarboxylation: All decarboxylation reactions of amino acids
require PLP as coenzyme. A few examples are given below:
a. Histidine  histamine, which is the mediator of allergy and
anaphylaxis.
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22. b. Methionine and cysteine metabolism.
c. Heme Synthesis: ALA synthase is a PLP
dependent enzyme. This is the rate limiting step in
heme biosynthesis. So, in B6 deficiency, anemia is
common.
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23. 3. Production of Niacin: Pyridoxal phosphate is
required for the synthesis of niacin from
tryptophan (one vitamin is necessary for synthesis
of another vitamin)
4. Glycogenolysis: Phosphorylase enzyme
(glycogen to glucose- 1-phosphate) requires PLP.
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24. 1. Dietary Sources
• Rich sources are yeast, rich polishing, wheat germs,
cereals, legumes (pulses), oil seeds, egg, milk, meat,
fish and green leafy vegetables.
1. Requirement
• Vitamin B6 requirement are related to protein intake
and not to calorie intake.
• Adults need 1 to 2 mg/day.
• During pregnancy and lactation, the requirement is
increased 2.5 mg/day.
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25. 5- PANTOTHENIC ACID
1.Structure
• The Greek eor "pantos" means everywhere. As the
name suggests, it is widely distributed in nature.
• Pantothenic acid contains beta alanine and pantoic
acid.
• Pantothenic acid and beta mercapto ethanol amine
are parts of coenzyme A (CoA).
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26. 2. Coenzyme Activity of
Pantathenic Acid
• The important CoA derivatives are: Acetyl-
CoA, Succinyl-CoA
• Coenzyme A is an important component of fatty
acid synthase complex. The ACP (acyl carrier
protein) also contains pantothenic acid.
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27. 6- BIOTIN
• Biotin acts as co-enzyme for carboxylation
reactions. Energy require for carboxylation
reactions is provided by ATP.
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28. 1. Biotin Requiring Co2 Fixation Reactions
i. Actyl-CoA carboxylase: This enzyme adds Co2 acetyl CoA to form
malonyl CoA. This the rate limiting reaction in biosynthesis of
fatty acids
• Acetyl CoA + Co2 + ATP  Malonyl CoA + ADP + Pi
i. Propionyl CoA carboxylase
• Propionyl CoA + Co2 +ATP  Methyl malonyl CoA + ADP +
Pi
i. Pyruvate carboxylase
• Pyuvate + Co2 + ATP  Oxaloacetate + ADP + Pi
• This reaction provides the Oxaloacetate, which is the catalyst
for TCA cycle. Second, it is important enzyme in the
gluconeogenic pathway.
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29. 2. Biotin-independent Carboxylation
Reaction
• Carbamoyl phosphate synthetase, which is the
stepping stone for urea and pyrimidine synthesis.
3. Biotin Antagonists
• Avidin, a protein present in egg white has great affinity to biotin.
Hence, intake of raw (unboiled) egg may cause biotin deficiency.
Biotin was originally named as anti-egg-white-injury-factor. One
molecule of avidin can combine with four molecules of biotin. It is
curious that egg white contains avidin and egg yolk contains biotin.
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30. • 4. Requirement of biotin
• About 200-300 mg will meet the daily
requirements.
• 5. Sources of biotin
• Normal bacterial flora of the gut will provide
adequate quantities of biotin. Moreover, it is
distributed ubiquitously in plant and animal
tissues. Liver, yeast, peanut, soybean, ilk, egg
yolk are rich source.
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31. 7- FOLIC ACID
• The latin word 'folium' means leaf of vegetable.
Folic acid is abundant in vegetables.
1.Chemistry of folic acid
• It is composed of three constituents. The pteridine
group linked with para amino benzoic acid (PABA)
is called pteroic acid. It is then attached to glutamic
acid to form pteroyl glutamic acid or folic acid
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32. 2. Coenzyme functions of folic
acid
A.The folic acid is reduced to tetrahydro folic acid
(THFA). This is catalyzed by NADPH dependent
folate reductase.
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33. 3. Sources of folic acid
• Rich sources of folate are yeast, green leafy vegetables.
Moderate sources are cereals, pulses, oil seeds and egg.
4. Recommended daily allowance
(RDA)
• The requirement of free folate is 200 microgram/day. In
pregnancy, the requirement is increased to 400
microgram/day and during lactation to 300
microgram/day.
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34. • 5. Folate Antagonists
• Solfonamides: They have structural similarity
with PABA. Bacteria can synthesize folic acid
from the compounds, pteridine, PABA and
glutamate. When sulfonamides are given,
microorganisms cannot synthesize folic acid and
hence their growth is inhibited. Thus,
sulphonamides are very good antibacterial
agents. Which do not affect the human cells.
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35. i. Methotrexate is powerful inhibitor of folate
reductase and THFA (tetrahydrofolic acid)
generation. Thus these drugs decrease the DNA
formation and cell division. It widely used as
anticancer drugs, especially for leukemias and
choriocarcinomas.
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36. 8- VITAMIN B12
1. Chemistry
i. Vitamin B12 is also called as cobalamin, antipernicious
anemia factor.
ii. Vitamin B12 is water soluble, heat stable and red in color.
It contains 4.35% cobalt by weight.
iii.It contains one cobalt atom. Four pyrrole rings coordinated
with a cobalt atom is called a corrin ring. The 6th valency of
the cobalt is satisfied by any of the following groups:
cyanide, hydroxyl, adenosyl or methyl.
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37. i. Hydroxy cobalamin: when hydroxyl group, it is
called hydroxy cobalamin or vitamin B12.
Injectable preparations are in this form.
ii.Adenosyl cobalamin (Ado-B12): This is the
major storage form.
iii.Methyl cobalamin: This is the major form seen
in blood circulation. The Ado-B12 and methyl
B12 are the functional coenzymes.
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38. 1.Absorption of vitamin B12
i. B12 complex is attached with specific receptors on mucosal
cells. The whole B12 complex is internalized.
2. Functional Role of B12
i. Methyl malonyl CoA isomerase: During the metabolism of
odd chain fatty acids, the propionyl CoA is carboxylated to
methyl malonyl CoA. It is then isomerized by methyl malonyl
isomerase or mutase (containing Ado-B12) to succinyl CoA,
which enters into citric acid cycle. In B12 deficiency, methyl
malonyl CoA is excreted in urine ( methyl malonic aciduria).
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39. 3. Requirement of vitamin B12
• Normal daily requirement is 1-2 microgram/day.
During pregnancy and laction, this is increased to
2 microgram/day.
4. Dietary sources
• Liver is the richest source. Curd is a good source,
because lactobacillus can synthesize B12
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