Vitamins and Coenzymes – Unit IV Comprehensive Study Notes

General Characteristics of Vitamins

  • Organic micronutrients that the body cannot synthesize in amounts needed for maintenance of health.
  • Essential for proper functioning of the body.
  • Human body can’t synthesize in enough amounts; therefore, enough vitamin can be obtained from a balanced diet.
  • Supplemental vitamins may be needed after illness.
  • Needed in micro- and milligram quantities.
  • 1 gram of vitamin B is sufficient for 500,000 people.1 extg extvitaminB<br/>ightarrow5imes105 extpeople.1~ ext{g}~ ext{vitamin B} <br /> ightarrow 5 imes 10^5~ ext{people}.
  • Many enzymes contain vitamins as part of their structures – conjugated enzymes.
  • B group vitamins act as coenzymes.

Major Classes by Solubility Characteristics

  • Water-soluble vitamins
    • Constantly replenished, rapidly eliminated from the body through kidneys.
    • Highly polar.
    • Carried in the bloodstream; needed in frequent, small doses; unlikely to be toxic except at unusually large doses.
    • With the exception of vitamin C, all water-soluble vitamins function as a coenzyme.
  • Fat-soluble vitamins
    • Dissolve in lipid material; non-polar molecular structures; can be dissolved in nonpolar solvents.
    • Classified as fats and have diverse functions; can act like hormones.
    • Carried in the blood by protein carriers; stored in fat tissues; needed in periodic doses; more likely to be toxic when consumed in excess.
    • Do not function as coenzymes.

Fat-Soluble Vitamins

  • ADEK (A, D, E, K)
  • Plus components of fat-soluble vitamins: A, D3, E, K2 (MK-7)

Vitamin A: Retinol

  • Retinoids: natural and synthetic analogs of retinol.
  • Structure overview (major forms): Retinol, Retinal (retinaldehyde), Retinoic acid, and β-carotene (provitamin A).
  • Derivatives:
    • retinal – aldehyde form
    • retinoic acid – acid form
  • Vitamin A is associated with rhodopsin formation in the eye.
Vitamin A: Biological Actions
  • Promotes growth and differentiation of tissues (also for reproduction).
  • Involved in glycoprotein synthesis.
  • Maintains integrity of tissues.
  • Antioxidant properties contribute to protective effects.
Vitamin A Deficiency
  • Early symptoms: defective night vision (nyctalopia / night blindness).
  • Keratinization: hardening of epithelial tissues in eyes, digestive tract, membranes, lungs, genito-urinary tract.
  • Xerophthalmia – can lead to blindness.
Vitamin A Excess
  • Hypervitaminosis A.
  • Teratogenic effects during pregnancy.
Benefits and Requirements
  • Maintains health of specialized tissues (e.g., retina).
  • Aids growth and health of skin and mucous membranes.
  • Promotes normal development of teeth, soft and skeletal tissue.
  • Adult RDA: extRDAA=1000 extμgRE.ext{RDA}_{A} = 1000~ ext{μg RE}.
  • Sources:
    • Animal sources: eggs, meat, dairy products.
    • β-carotene (provitamin A): green leafy vegetables and intensely colored fruits/vegetables.
  • Storage: stored in liver.
Vitamin A Sources (Summary)
  • Animal sources: eggs, meat, dairy products.
  • β-carotene sources: green leafy vegetables and brightly colored fruits/vegetables.

Vitamin D

  • Forms: Ergocalciferol (D₂) and Cholecalciferol (D₃).
    • D₂: made in plants; D₃: formed in animals.
    • Both forms of equal potency.
Vitamin D: Biological Actions
  • Facilitates absorption of Ca and P into the body; calcium is deposited in bones.
  • Required for proper biological activity of the parathyroid hormone.
Vitamin D Deficiency
  • Rickets (in childhood): low plasma Ca and P; poorly mineralized bones; skeletal deformities.
  • Osteomalacia (in adults): decreased Ca and P absorption; impaired mineralization of bones (weak).
  • Osteoporosis: decalcification/softening of bones.
Vitamin D Excess
  • ↑ blood Ca; calcification of soft tissues.
Requirements and Sources
  • DRI: extDRI=5 extμg.ext{DRI} = 5~ ext{μg}.
  • Sources: the body can synthesize vitamin D with sun exposure; dietary sources include cheese, butter, margarine, fortified milk, fish, fortified cereals.
  • Note: Sun exposure is a major natural source of vitamin D.

Vitamin E

  • Primary form: α-tocopherol; exists as α-, β-, δ-, γ-tocopherol; α-tocopherol is the most potent.
  • Vitamin E family includes tocopherols and tocotrienols.
    • α-tocopherol (A) and α-tocotrienol (B) are identical except for unsaturation in the side chain.
  • α-tocopherol has widest natural distribution and greatest biological activity.
Vitamin E: Biological Actions
  • Protects polyunsaturated fatty acids from peroxidation; maintains integrity of cell membranes (skin, blood cells, etc.).
Interaction with Selenium
  • Selenium is needed for normal pancreatic function.
  • Tocopherol and Se reinforce each other in defense against lipid peroxidation.
Vitamin E Deficiency
  • Anemia in newborn infants (due to decreased Hb production and shortened RBC lifespan).
  • Neurologic disorders in adults.
Vitamin E Benefits
  • Protects cell membranes and tissues from oxidative damage.
  • Aids in the formation of red blood cells and the use of vitamin K.
  • Promotes function of a healthy circulatory system.
  • Adult RDA: ext{RDA}_{E} = 10~ ext{mg } oldsymbol{ ext{α-TE}}.
  • Sources: corn, nuts, olives, green leafy vegetables, vegetable oils, wheat germ; supplementation may be helpful.

Vitamin K

  • Formes: Phylloquinone (K₁) and Menaquinones (K₂).
  • K₁ is the major form in plants; K₂ is found in animals and humans.
  • Vitamin K designation derives from Danish word Koagulation (coagulation).
Vitamin K: Biological Actions
  • Essential for the formation of prothrombin.
  • Involves biosynthesis of other clotting proteins found in plasma, bone, and kidney.
Vitamin K Deficiency
  • Bleeding/hemorrhage.
Vitamin K Requirements
  • Adult RDA: 70 extμg.70~ ext{μg}.
  • Fat-soluble.
Vitamin K Sources
  • Food sources include cabbage, cauliflower, spinach and other green leafy vegetables, as well as cereals.

Summary Table (Vitamin Sources, Functions, and Deficiency Conditions)

  • Vitamin A (retinol): Fat-soluble; sources – eggs, butter, cheese, dark green and deep orange vegetables; function – synthesis of visual pigments; deficiency – night blindness, inflamed eye membranes, keratinization; deficiency signs include xerophthalmia.
  • Vitamin D (calciferol): Fat-soluble; sources – fish-liver oils, fortified milk; function – regulation of calcium and phosphorus metabolism; deficiency – rickets, osteomalacia, osteoporosis; DRI ≈ 5 extμg.5~ ext{μg}.
  • Vitamin E (tocopherol): Fat-soluble; sources – whole-grain cereals, margarine, vegetable oil; function – prevention of oxidation; deficiency – breakage of red blood cells; signs include dermatitis and anemia.
  • Vitamin K: Fat-soluble; sources – cabbage, leafy greens; function – synthesis of blood-clotting substances; deficiency – bleeding disorders.

Water-Soluble Vitamins (Overview)

  • B vitamins (B1–B12) and Vitamin C; generally not stored in large amounts; excess usually excreted; many act as coenzymes in energy metabolism, amino acid metabolism, and nucleic acid synthesis.
Vitamin B1 (Thiamine)
  • Structure: central C attached to a six-membered heterocyclic ring and a five-membered thiazole ring (thio- + -amine).
  • Coenzyme form: thiamine pyrophosphate (TPP).
  • Major function: group transfer reactions (e.g., removal of COOH group in oxidative decarboxylation) and the pentose phosphate shunt.
  • Deficiency: Beriberi (nerve degeneration); Wernicke’s encephalopathy (in alcoholics).
  • RDA: 1.5 extmg.1.5~ ext{mg}. (Water-soluble)
  • Sources: fortified breads and cereals, fish, lean meats, milk.
Vitamin B2 (Riboflavin)
  • Formerly called the yellow vitamin; flavin in Latin means yellow.
  • Structure: three fused six-membered rings with a ribose sugar.
  • Coenzyme forms: FAD and FMN.
  • Major function: oxidation-reduction reactions.
  • Deficiency: cheilitis, glossitis, dermatitis; photophobia; anemia; erythroid hypoplasia.
  • RDA: 1.7 extmg.1.7~ ext{mg}. (Water-soluble)
  • Sources: cereal, nuts, milk, eggs, green leafy vegetables, lean meat.
Vitamin B3 (Niacin)
  • Forms: Nicotinic acid and Nicotinamide; both forms convert to the same coenzymes.
  • Coenzyme forms: NAD⁺ and NADP⁺.
  • Major function: oxidation-reduction reactions.
  • Deficiency: Pellagra — dermatitis, glossitis, diarrhea, dementia; other symptoms include weakness, skin problems.
  • RDA: 19 extmg.19~ ext{mg}. (Water-soluble)
  • Sources: dairy, poultry, fish, lean meat, nuts, eggs.
Vitamin B5 (Pantothenic Acid)
  • Also called Vitamin B5.
  • Structure: pantothenate group with a pantothenic acid moiety.
  • Found widely in foods; “pantothen” means everywhere.
  • Coenzyme forms: Coenzyme A (CoA) and Acyl carrier protein (ACP).
  • Major function: acyl transfer reactions; transport of fatty acids.
  • Deficiency: gastrointestinal disturbances; depression; anemia.
  • Sources: widespread; egg yolk, lean meat.
Vitamin B6 (Pyridoxine, Pyridoxal, Pyridoxamine)
  • Collective term for three related compounds.
  • Sources: Pyridoxine from plants; Pyridoxal and Pyridoxamine from animal sources.
  • Coenzyme form: pyridoxal-5'-phosphate (PLP); also PNP and PMP.
  • Major function: group transfer (transamination), carboxyl group transfer, and heme synthesis.
  • Deficiency: dermatitis, nervous disorders, convulsions; chronic anemia; peripheral neuropathy.
  • RDA: 2 extmg.2~ ext{mg}. (Water-soluble)
  • Sources: beans, legumes, nuts, eggs, meats, fish, breads and cereals.
Vitamin B7 (Biotin)
  • Obtained via diet or biotin-producing bacteria in the gut.
  • Structure: two fused rings containing S and N with a pentanoic acid residue.
  • Coenzyme form: biotin.
  • Major function: carboxylation reactions; fatty acid synthesis; also involved in conversion of pyruvate to oxaloacetate during protein metabolism.
  • Deficiency: dermatitis; nausea; depression; muscle weakness; sometimes immunodeficiency in children.
  • Sources: widely distributed in foods; meat, poultry, whole-grain cereals, broccoli, beans.
Vitamin B9 (Folate / Folic Acid)
  • Structure: pteridine ring with p-aminobenzoic acid (PABA) and one or more glutamate residues; leaf-derived folate is abundant.
  • Important for synthesis of nucleic acids; essential for fetal brain, skull, and spinal cord development.
  • Coenzyme form: tetrahydrofolate (THF).
  • Major function: transfer of 1-carbon groups (methylation) for nucleic acid precursors.
  • Deficiency: Megaloblastic anemia.
  • Food sources: leafy green vegetables, peas, beans, citrus fruits/ juices, whole grains, poultry, liver.
Vitamin B12 (Cobalamin)
  • Structure: contains cobalt; complex ring with multiple amine groups.
  • Coenzyme forms: methylcobalamin and deoxyadenosylcobalamin.
  • Major function: transfer of alkyl groups and hydrogen atoms; important in gluconeogenesis; maintains methionine and THF structures.
  • Deficiency: pernicious anemia; methylmalonyl-CoA mutase deficiency can cause methylmalonic acidemia with respiratory/gastrointestinal symptoms; neurological damage with demyelination.
  • Sources: animal products (eggs, meat, poultry, shellfish, milk and dairy).
Vitamin C (Ascorbic Acid)
  • Exists in oxidized and reduced forms.
  • All plants and animals can obtain it from glucose derivatives.
  • Biological actions:
    • Hydroxylation reactions
    • Collagen synthesis
    • Degradation of tyrosine
    • Synthesis of epinephrine from tyrosine
    • Bile acid formation
    • Enhances iron absorption
    • Major antioxidant
  • Deficiency: scurvy (soft swollen gums, loose teeth; defective collagen synthesis; hemorrhages; muscle weakness).
  • RDA: 60 extmg.60~ ext{mg}. (Water-soluble)
  • Sources: citrus fruits, strawberries, tomatoes, green peppers, broccoli, potatoes.
Summary: Vitamin Sources, Functions, and Deficiency Conditions (Key Points)
  • B vitamins are water-soluble and function mainly as coenzymes in energy metabolism, amino acid metabolism, and nucleic acid synthesis.
  • Vitamin C supports collagen synthesis and acts as a major antioxidant; deficiency leads to scurvy.
  • Vitamins A, D, E, and K are fat-soluble with storage in tissues and distinct roles in vision, bone health, antioxidant protection, and blood clotting, respectively.
  • Deficiency conditions range from Beriberi (B1) and Pellagra (B3) to Megaloblastic anemia (B9) and Pernicious anemia (B12), among others.
Quick Reference: Representative Numeric Values
  • Vitamin A: extRDAA=1000 extμgREext{RDA}_{A} = 1000~ ext{μg RE}
  • Vitamin D: extDRI=5 extμgext{DRI} = 5~ ext{μg}
  • Vitamin E: ext{RDA}_{E} = 10~ ext{mg } oldsymbol{ ext{α-TE}}
  • Vitamin K: extRDAK=70 extμgext{RDA}_{K} = 70~ ext{μg}
  • Vitamin B1: extRDAB1=1.5 extmgext{RDA}_{B1} = 1.5~ ext{mg}
  • Vitamin B2: extRDAB2=1.7 extmgext{RDA}_{B2} = 1.7~ ext{mg}
  • Vitamin B3: extRDAB3=19 extmgext{RDA}_{B3} = 19~ ext{mg}
  • Vitamin B6: extRDAB6=2 extmgext{RDA}_{B6} = 2~ ext{mg}
  • Vitamin C: extRDAC=60 extmgext{RDA}_{C} = 60~ ext{mg}

Note: This set of notes mirrors the content and emphasis from the provided transcript passages, including major and minor points, deficiency symptoms, sources, and standard RDAs where stated. Numerical values are presented in LaTeX format as requested for clarity and exam preparation.