Lipid vitamins

Lesson 15 : Enzymes- Coenzymes and Co-Factors

Lipid vitamins

Vitamin A or retinol

  1. Is a 20 carbon lipid molecule.
  2. Found in carrots, yellow vegetables, liver, egg yolk, milk products.
  3. ?-carotene ---> vitamin A

  4. Exists in three forms:
    • retinol and
    • retinoic acid - binds to intracellular protein receptors --> regulates gene expression retinal - prosthetic group of rhodopsin-involved in dark adaption and night vision.

Vitamin D

  1. Exists as several lipids;

    • D3 - made in skin exposed to sunlight.
    • D2 - additive in fortified milk

  2. Deficiency causes rickets in children or osteomalacia in adults --> insufficient Ca phosphate deposition in bone.

Vitamin E or tocopherol

  • Is an antioxidant that scavenges free radicals.

Vitamin K or phylloquinone

  • Found in plants.
  • Required for synthesis of proteins involved in blood coagulation.

Ubiquinone or coenzyme Q

  1. Ring with hydrophobic tail --> inserted into membranes.
  2. Transports e- between enzyme complexes in inner mitochondrial membrane.
  3. Related molecule is plastiquinone - found in thylacoid membrane of chloroplasts.


  • Heme-containing protein coenzyme Fe3+ <--> Fe2+.
  • Classified as a, b, c based on absorption spectra.
  • Transfers e-.
Last modified: Friday, 20 January 2012, 6:46 AM