Vitamins and co-enzymes | Zoology Optional Notes for UPSC PDF Download

Vitamins: Essential Organic Compounds for Life

Definition and Importance:

• Vitamins are organic compounds necessary for sustaining life.
• Obtained from food since the human body either doesn't produce enough or doesn't produce them at all.

Biological Functions:

• Vitamins play crucial roles in various biological functions within the body.
• Most importantly, they serve as cofactors (co-enzymes) for enzymatic reactions.

Cofactors and Enzymes

Enzyme Formation:

• Protein + Coenzyme (Vitamin) = Enzyme
• Protein + Cofactor (Metal Ion) = Enzyme

Dietary Requirement:

• Vitamins cannot be synthesized by mammalian cells and must be supplied in the diet in small quantities (microgram or milligram per day).

Key Terms:

• Enzyme: A protein that acts as a catalyst, facilitating specific biochemical reactions.

• Cofactor: A small, inorganic, or organic substance that enhances enzyme action. It Includes organic coenzymes (derived from vitamins) and inorganic substances like minerals.

• Coenzymes: Non-protein organic molecules, mostly vitamin derivatives soluble in water. Bind to apoenzyme, forming an active holoenzyme.

• Prosthetic Group: A cofactor permanently associated with the protein, often covalently bound.

• Holoenzyme: A catalytically active enzyme-cofactor complex.

• Apoenzyme: An enzyme without its cofactor, rendering it enzymatically inactive.

• Free Radicals: Unstable and highly reactive atoms or molecules with one or more unpaired electrons in the outer orbital.

Vitamins are essential organic compounds vital for various biological functions, acting as cofactors in enzymatic reactions. Enzymes, the catalysts of biochemical reactions, often require cofactors like coenzymes, which are derived from vitamins. The terms holoenzyme, apoenzyme, and prosthetic group describe the active enzyme-cofactor complex, the inactive enzyme without its cofactor, and a cofactor permanently associated with the protein, respectively. Additionally, free radicals, unstable and reactive entities, play a role in cellular processes.

Water-Soluble Vitamins

Vitamin B1 - Thiamine:

• Active Form: Thiamine Pyrophosphate (TPP).
• Functions:
  • Essential coenzyme in energy extraction and cellular processes.
  • Required for decarboxylation in the citric acid cycle.
  • Necessary for transketolase reaction in glucose metabolism.
• Sources: Unpolished rice, wheat germ, cereals, pulses, nuts, oils, meat, fish, milk, and vegetables.
• Deficiency (Beriberi):
  • Gastrointestinal issues, cardiovascular problems, and neurological disorders.

Vitamin B2 - Riboflavin:

• Active Form: Riboflavin Phosphate.
• Functions:
  • Component of coenzymes FAD and FMN.
  • Essential for cellular processes, oxygen transfer, and metabolism of fats, ketone bodies, carbohydrates, and proteins.
• Sources: Milk, egg, liver, leafy vegetables.
• Deficiency (Cheliosis, Glossitis, Photophobia).

Vitamin B3 - Niacin:

• Active Form: Nicotinic Acid.
• Functions:
  • Forms NAD and NADP.
  • Sources: Liver, milk, tomato.
• Deficiency (Pellagra):
  • Manifested by dermatitis, diarrhea, and dementia.

Pantothenic Acid (Vitamin B5):

• Function: Used in the synthesis of coenzyme A (CoA).
  • CoA is crucial in energy metabolism, fatty acid, and cholesterol synthesis.
• Deficiency: Graying of hair, growth failure, and hair loss.

Vitamin B6 - Pyridoxal (Pyridoxine):

• Functions:
  • Derivative of pyridine molecule.
  • Involved in various cleavage reactions.
  • Responsible for decarboxylation and transamination reactions.
• Deficiency: Epileptiform convulsions, peripheral neuritis, microcytic hypochromic anemia.

Biotin (Vitamin B7):

• Source: Egg yolk, liver, kidney, yeast, milk, tomatoes.
• Functions:
  • Acts as a coenzyme in carboxylation reactions.
  • Involved in fatty acid, carbohydrate, amino acid, and purine synthesis.
• Deficiency: Nausea, anorexia, anemia, muscular pain.

Vitamin B9 - Folic Acid:

• Synthesized from: Pteridine, glutamic acid, and p-amino benzoic acid (PABA).
• Active Form: Tetrahydrofolate (THF).
• Functions:
  • Acts as a coenzyme in single carbon transfer reactions.
  • Essential for nucleic acid synthesis and maturation of RBC.
• Deficiency: Megaloblastic anemia.

Vitamin B12 - Cyanocobalamin:

• Source: Leafy vegetables, kidney, liver, meat, milk.
• Functions:
  • Acts as a coenzyme in methyl group transfer and RNA to DNA conversion.
  • Requires intrinsic factor for absorption.
• Deficiency (Pernicious Anemia):
  • Atrophy of mucous membrane, lesions in the central nervous system.

Lipoic Acid:

• Function: Acts as a coenzyme in the oxidative decarboxylation of pyruvic acid and α-ketoglutaric acid.

Vitamin C - Ascorbic Acid:

• Source: Citrus fruits, berries, cabbage, tomatoes.
• Functions:
  • Necessary for fibroblast and osteoclast activity.
  • Synthesizes collagen, operates oxidation-reduction reactions, aids iron absorption.
• Deficiency (Scurvy):
  • Painful joints, defective teeth, bone formation, hemorrhage.

Lipid-Soluble Vitamins

Vitamin A:

• Forms: Retinol, Retinal, Retinoic acid.
• Derived from: Carotenoids (provitamin A).
• Functions:
  • Essential for growth, reproduction, bone and teeth formation.
  • Maintains epithelium of skin and mucous membranes.
  • Antioxidant effect, synthesizes rhodopsin for vision.
• Deficiency: Night blindness, xerophthalmia, keratomalacia.

Vitamin D:

• Forms: D2 (ergocalciferol), D3 (cholecalciferol).
• Source: Shark liver oil, cod liver oil, egg yolk.
• Functions:
  • Facilitates calcium and phosphorus absorption, bone development.
  • Reduces the risk of rickets.
• Deficiency: Rickets in children, osteomalacia in adults. Excess leads to tissue calcification and renal calculi.

Vitamin E - Tocopherol:

• Forms: α, β, γ forms (α-active form).
• Source: Sunflower oil, wheat germ oil, soybean, egg, meat, fish.
• Functions:
  • Antioxidant, prevents sterility.
  • Prevents damage to vitamin A and fatty acids.
• Deficiency: Sterility, intrauterine death, muscle dystrophy, weakness, paralysis.

Vitamin K:

• Forms: K1 (phylloquinone), K2 (farnoquinone), K3 (menadione).
• Functions:
  • Necessary for blood coagulation, activates prothrombin factors.
  • Acts as an antidote for anticoagulant drugs.
• Deficiency: Bleeding, hemorrhage, can be caused by antibiotic administration and malabsorption due to pancreatic disease.