biochemistry

1. Vitamins and coenzmes
Learning objectives:
1.Learn the Definition of Vitamins
2.Study the Classification of Vitamins
3.Learn the Dietary sources of Vitamins
4.Learn the functions of vitamins
5.Learn the deficiency diseases of Vitamins
6.Learn the Coenzymes derived from Vitamins

2. Definitions
Vitamins ?
• Vitamins are organic compounds required in the diet in small
amounts for proper growth and good health.
Coenzymes:
• A coenzyme is a non protein part of an enzyme.
• An enzyme is made up of a protein and a non protein part.
• The protein part of the enzyme is known as
the apo-enzyme.
• The coenzyme and apoenzyme combine to form holo-
enzyme.
• Some coenzymes are derived from Vitamins .

3. Classification of Vitamins
1.Fat soluble Vitamins
2.Water soluble Vitamins
Fat soluble Vitamins:
• Vitamin A
• Vitamin D
• Vitamin E
• Vitamin K
Water soluble Vitamins:
• Vitamin C and B complex.

4. Vitamin A
• Vitamin A refers to a group of compounds
known as Retinoids .
• They include: Retinol ,Retinal and Retinoic
acid .
Beta carotene:
• Beta carotene is Provitamin A
• It is found in plant foods
• It is an antioxidant.

5. Dietary sources of Vitamin A
Animal Sources of Vitamin A:
• Liver, Egg yolk, Milk, Cheese, Butter and Fish liver
oils.
Plant sources of Vitamin A:
• Yellow vegetables and fruits like Carrots,Mangoes
,pumpkins and papayas.
• Dark green vegetables e.g Spinach and Amaranthus.

6. Functions of Vitamin A
• It enhances Vision
• It enhance proper growth and reproduction
• It mantains epithelial cells
• It has an antioxidant property hence prevents cancers
Deficiency diseases of Vitamin A:
• Night blindness-Difficult to see in dim light
• Xeropthalmia- conjunctiva becomes dry, thick and
wrinkled.
• Keratomalacia - softening of the cornea

7. Vitamin A structure

8. Vitamin D
• Vitamin D3(Cholecalciferol)-in animals
• Vitamin D2 (Ergocalciferol)-in plants
Main source of vitamin D:
• Vitamin D is mainly obtained from sun-shine .
Dietary sources of Vitamin D:
• Fish liver oils
• Egg yolk
• Margarine

9. Biosynthesis of Vitamin D:
• 7-dehydrocholesterol is formed as an intermediate in
cholesterol biosynthesis.
• On exposure to sunlight,7-dehydrocholesterol is
converted to cholecalciferol in the skin.
Functions of Vitamin D:
1.Vitamin D increases the intestinal absorption of
Calcium and phosphate.
2. It is essential for bone formation .
3.It enhances reabsorption of calcium and phosphate in
the kidney

10. Deficiency diseases of Vitamin D
1.Rickets in children
• Bone deformities .
• Delay in teeth formation.
2.Osteomalacia in adults
• Demineralization of the bones.
• softening of bones.

11. Vitamin E
• Vitamin E (tocopherol)
• It is the most powerful antioxidant
Dietary sources of Vitamin E:
Vegetable oils e.g;
• wheat germ oil
• peanut oil
• corn oil
• sunflower oil.

12. Functions of Vitamin E
1.It is the most powerful antioxidant.
2.It mantains the membrane structure and integrity of
the cell.
Deficiency of Vitamin E:
• Muscle weakness.
• Hemolysis of red blood cells.

13. Vitamin E structure

14. Vitamin K
Types:
• Vitamin K1 - in plants.
• Vitamin K2 –produced by intestinal bacteria and
found in animals.
• VitaminK3 - a synthetic form.
Dietary sources:
• Spinach, green vegetables ,egg yolk, meat, liver
and cheese

15. Functions of Vitamin K
• For formation of blood clotting factors e.g
Prothrombin.
• For formation of Coenzyme Q (ubiquinone) .
Deficiency of Vitamin K:
• Blood coagulation is adversely affected.
• The individual bleeds heavily even for minor
injuries.

16. Vitamin K1

17. Vitamin K2

18. Vitamin K3

19. Water soluble Vitamins
Vitamin C:
• Also known as Ascorbic acid .
Dietary Sources:
• Fruits and vegetables e.g cabbage ,spinach ,Tomatoes
and Potatoes.
Functions of Vitamin C:
1.Vitamin C helps in hydroxylation of proline &lysine
2. It is required for bone formation.
3.It enhances iron absorption

20. Functions of Vitamin C contd
4. It is an antioxidant.
5. It is needed for the formation of FH4
6.It helps to convert methemoglobin to hemoglobin
7. It is essential for the formation of Serotonin
8.It is involved in tyrosine metabolism.
9. It enhances the synthesis of antibodies &
increases the phagocytic action of leucocytes
Deficiency disease:
• Deficiency of Vitamin C causes Scurvy.

21. Manifestations of Scurvy
• Microcytic anemia .
• Weak bones .
• Wound healing is delayed.
• Loss of teeth.
• Hemorrhagic tendency

22. Structure of Ascorbic acid

23. Vitamin B Complex
• Thiamine(B1)
• Riboflavin(B2)
• Niacin(B3)
• Pantothenic acid(B5)
• Pyridoxine(B6)
• Biotin(B7)
• Folic acid(B9)
• Cynocobalamin(B12)

24. Thiamine(Vitamin B1)
• Thiamine is involved in carbohydrate metabolism.
• The co-enzyme derived from Thiamine is Thiamine
Pyrophosphate (TPP).
Roles of TPP:
• TPP is used in oxidative decarboxylation of Pyruvate
to acetyl COA by pyruvate dehydogenase.
• TPP is used in Transketolation reactions by
transketolases in the hexose monophosphate shunt
pathway.

25. Dietary Sources of Thiamine
• Outer layer of food grains e.g whole wheat flour
and unpolished rice.
Deficiency disease:
• Deficiency of thiamine leads to Beriberi
Types of BeriBeri:
• Dry beriberi
• wet beriberi.

26. Dry beriberi
• CNS manifestations.
• Walking becomes difficult.
• Peripheral neuritis with sensory disturbance leads to
complete paralysis.
Wet BeriBeri:
• Cardiovascular manifestations:
• Edema of legs&face
• Heart failure.

27. Structure of Thiamine

28. RIBOFLAVIN (VITAMIN B2)
• It is synthesized by the instestinal flora in man.
• Coenzyme forms are:
i) FMN (Flavin Mono Nucleotide)
ii) FAD (Flavin Adenine Dinucleotide)
• They act as coenzymes for hydrogen transfer
reactions in metabolism.
Sources :
• Liver, Eggs ,Milk,Fish,Whole cereals and Green
leafy vegetables.

29. FAD and FMN Dependent Enzymes
FAD-dependent Enzymes
• Succinate dehydrogenase
• Xanthine oxidase
• Pyruvate dehydrogenase
• Alpha ketoglutarate dehydrogenase
FMN-dependent Enzymes:
• Amino acid oxidases
• NADH dehydrogenase

30. Riboflavin Deficiency
i. Lips: Redness and shiny appearance of lips
ii. Magenta colored(red purple) tongue
iii. Cheilosis - lesions on the corners of the
mouth
iii) Seborrhoeic dermatitis: lesions on the ears
and nose
iv)photophobia

31. Structure of Riboflavin

32. NIACIN
• Also known as Nicotinic acid.
• Niacinamide is the active form of the vitamin, present in
tissues.
• Niacin is synthesized from tryptophan
Sources:
• Whole cereals,Liver,Meat and Fish.
Coenzymes derived from Niacin:
• Nicotinamide adenine dinucleotide (NAD+)
• Nicotinamide adenine dinucleotide phosphate
(NADP+).

33. NAD+ Dependent Enzymes:
• Lactate dehydrogenase (lactate → pyruvate)
• Pyruvate dehydrogenase (pyruvate → acetyl CoA)
• Alpha ketoglutarate dehydrogenase (alpha ketoglutarate→
succinyl CoA
Deficiency disease of Niacin:
• Pellagra- rough skin
Symptoms of pellagra:
1.Dermatitis-increased pigmentation in the face,feet,ankles and
neck
2.Diarrhea: This leads to weight loss.
3.Dementia: Irritability ,Lack of concentration and Poor memory

34. Niacin deficiency

35. Structure of Niacin

36. PANTOTHENIC ACID (VITAMIN
B5)
• Pantothenic acid consists of β-alanine in peptide
linkage with Pantoic acid .
• Active form is coenzyme A.
• It is synthesized by intestinal bacteria in humans.
Sources:
• Liver ,Eggs,cereals ,Milk,Sweet potatoes,Fish
and Intestinal flora.

37. Coenzyme form of Pantothenic acid
• Coenzyme A (CoA).
Roles of CoA:
Acetyl COA is involved in:
• Acetylation reactions
• ketogenesis
• cholesterol synthesis.
• Fatty acid synthesis.
Deficiency:
• No deficiency disease has been recognized in man.

38. Structure of Pantothenic Acid

39. VITAMIN B6
• Vitamin B6 refers to pyridine derivatives;
i) Pyridoxine
ii) Pyridoxal
iii) Pyridoxamine.
• Coenzyme form of pyridoxine is pyridoxal phosphate
(PLP).
Sources of Vitamin B6:
• Cereals,Eggs,milk,meat,Fish and green leafy vegetables.

40. Functions of Vitamin B6
1.The pyridoxal phosphate (PLP) acts as co-
enzyme in amino acid metabolism e.g
a) Transamination reactions
Alanine + Alpha keto glutarate → Pyruvate +
Glutamic acid by Alanine transaminase
b)Decarboxylation reactions
• Glutamate → GABA (gamma amino butyric
acid) by glutamate decarboxylase

41. Functions of Vitamin B6 Cont
2.PLP is involved in conversion of Homocysteine
to Cystathionine.
3.PLP is required by ALA synthase which
catalyzes rate limiting step in heme synthesis.
4.Pyridoxal phosphate is required for the
synthesis of niacin from tryptophan

42. Deficiency Manifestations of
Pyridoxine
• Neurological Manifestations- serotonin,
epinephrine,noradrenalin and gamma amino
butyric acid (GABA)are not produced properly.
2. Dermatological Manifestations –Vitamin B6
deficiency in turn leads to niacin deficiency
which is manifested as pellagra.
3. Hematological Manifestations- anemia
due to the inhibition of heme synthesis.

43. Structure of Pyridoxine and Pyridine
derivatives

44. Biotin
Sources of Biotin:
• Liver , milk , egg yolk and Intestinal bacteria.
Functions of Biotin:
• Biotin is involved in carboxylation reactions
catalysed by Carboxylases e.g
1.Pyruvate carboxylase.
2.Acetyl COA Carboxylase.
Deficiency of Biotin :
• Dermatitis,Glossitis and Anorexia

45. BIOTIN

46. Folic acid
• Tetrahydrofolate( F.H4) is the Coenzyme .
Sources:
• Liver, green leafy vegetables, Spinach , Meat
Fish and Intestinal bacteria in humans
Function of tetrahydrofolate :
• It transfers one carbon compounds e.g Methyl (–
CH3) and formyl (–CHO)
Deficiency of Folic acid:
• Macrocytic Anaemia

47. FOLIC ACID(Vitamin B9)

48. VITAMIN B12
It is also known as:
• Cobalamin/ Cyanocobalamin/Antipernicious
anaemia factor/Extrinsic factor of Castle
Sources of Vitamin B12:
• Liver(richest source),Eggs, Fish, Meat , Curd milk
Coenzyme for the enzymes:
• Methylmalonyl COA isomerase
• Homocysteine methyl transferase

49. Deficiency of Vitamin B12
Deficiency disease:
• Pernicious anaemia.
Symptoms:
• Methyl Malonic Aciduria.
• Cardiovascular disease
• Stroke
• Memory loss
• Depression

50. Chemistry of Vitamin B12
• It has 4 pyrrole rings co-ordinated with a cobalt atom.
• Cobalt is covalently linked to a substituted
benzimidazole ring. This is called cobalamin.
• The cobalt is also linked by any of the following
groups: cyanide, hydroxyl, adenosyl or methyl.

51. structure of Vitamin B12