Define vitamin

• primary- lack of vitamin in diet
• secondary- vitamin in diet, but cannot be utilized (ex: malabsorption)

Classification of vitamins

• fat soluble
• water soluble

• K (menaquinone)
• A (retinol)
• D (cholecalciferol)
• E (tocopherols)

• C (ascorbic acid)
• B complex vitamins

• biotin
• folic acid
• hydroxycobalamin
• niacin
• pantothenic acid
• pyridoxine
• riboflavin
• thiamine

• normal state
• deficiency state
• excessive intake/toxicity

• due to the fact the liver has been catabolizing vitamin C in higher levels, the person would get scurvy

• fat absorption mechanism
  1. vitamin fits into the micelle
  2. moves to enterocyte and vitamin enters cell
  3. form chylomicrons (vitamin usually on outside with fat in the middle)
  4. goes to the lymphatic system, then back into blood where it hits the heart
  5. fat is removed by adipose and muscle
  6. end up in the liver

• fat cannot be absorbed

dissolves in the membrane, and function as anti-oxidant

Chemical structure of vit. K

• protein modification
• addition of carboxyl group to Glu residues in certain proteins (Factors II, VII, IX, X)

rickets

osteomalacia

Three forms of vitamin A

retinol (primary alcohol)

retinal (aldehyde)

retinoic acid (carboxylic acid)

• substituted hexene ring
• side chain- conjugated double bond structure with all double bonds in trans configuration

three forms can be inter-converted in the body, EXCEPT retinoic acid cant be reduced to retinal

• oxidative cleavage of most central double bond in isoprenoid chain of carotinoid
• ex: breaking beta carotene gives me two retinals
• location- liver and intestinal cells 

• removed from stores via hydrolysis
• released and transported to tissue bound to the retinol binding protein

• vision
• growth (bone dev. in kids)
• reproduction
• maintenance and differentiation of epithelial cells

Retinoic acid does not function in vision or reproduction.

1. trans retinol oxidized to trans retinal
2. retinal converted to 11 cis isomer which binds to membrane protein opsin
   1. this complex is now called rhodopsin
3. rhodopsin absorb photon of light and is activated (becomes metarhodopsin II)
4. causes activation of transducin (trimeric G protein), causing dissociation of G protein subunits
5. α subunit binds GTP, which binds phosphodiesterase and removes its inhibitor (phosphodiesterase now active)
6. PDE hydrolyze cGMP
7. decrease in cGMP inactivates cGMP dependent gated ion channel that transport calcium and sodium
8. membrane hyperpolarized
9. nerve impulse generated

• three different opsins each of which bind 11-cis retinal
• three different opsins absorb light at three different wavelengths
  • blue- 425 nm
  • green- 530 nm
  • red- 560 nm

• retinoic acids function as hormones
  • two nuclear receptors: RAR and RXR for retinoic acid
  • receptor functions as dimer (can be homodimer or heterodimer) bound to the hormone response element (HRE) in DNA
  • the retinoic acid-receptor complex controls expression of specific mRNA

Ex: those for keratins in epithelial cells

• night blindness
• xeropthalmia
• keratosis

in dim light, it takes eyes longer to adjust to changes in light intensity

• drying of cornea and conjunctiva
• results in ulceration and blindness if not treated

• dryness and rouhgness of skin with masses of keratinized epithelium which appear like "goose flesh"
• cause- squamous epithelium converted to stratified squamous epithelium
  • proposed that stratified squamous epithelia may be pre-cancer form

• heptamegaly with cirrhosis
• skin dry and pruritic
• increase intracranial pressure

• excess can be converted to retinoids
• retinoids cause fetal malformation

Use of treinoin and its chemical structure

• topical treatment for acne, psoriasis (its very toxic if you take orally)
• chem struc.- all trans retinoic acid

• oral medication for sever acne
• chemical structure- 13 cis retinoic acid

• carbohydrate (hexose)
• contain internal lactone linkage and an enediol group

• lactone hydrolyze in presence of divalent metal ions
• yields 2,3 diketo L gulonic acid (NO biological activity)

• function in oxidation/reduction reactions
  • coenzymes for several mono-oxygenases
    • prolyl-MO (involved in collagen biosynthesis)
    • lysyl- MO (involved in collagen biosynthesis)

• via prolyl monooxygenase, oxygen used and forms water
• vit. C is coenzyme
• end with 4-OH prolyl

Product of Lysyl MO rxn on alpha chain of collagen

• due to defective collagen biosyn.
  • defective bone formation (infants) (bow legs)
  • swollen, bleeding gums,
  • bruising
  • poor wound healing

fruits

tomatoes

green vegetables

• irritation of GI tract
• precipitation of uric acid and/or oxalate
  • with formation of kidney stones
• increase cation absorption (especially iron)

• infants
• food faddists (try "weird" diets)
• alcoholics
• elderly