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Medical Biochemistry Robert F. Waters, PhD

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Medical Biochemistry Robert F. Waters, PhD. Lipid Overview. Medical Biochemistry II: Lipids. Fatty Acid Overview:. Fatty Acid Nomenclature. Delta System Omega System Saturated vs. Unsaturated Cis vs. Trans Carbon Numbering Alpha carbon, etc. Fatty Acid Structure.

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fatty acid nomenclature
Fatty Acid Nomenclature
  • Delta System
  • Omega System
  • Saturated vs. Unsaturated
  • Cis vs. Trans
  • Carbon Numbering
  • Alpha carbon, etc.
fatty acids and good and bad cholesterol
Fatty Acids and “Good and Bad Cholesterol”
  • Saturated FA
    • Raise Good and Bad Cholesterol
  • Monounsaturated FA
    • Raise HDLs and Lower LDLs
  • Polyunsaturated FA
    • Maintain HDLs and Lower LDLs
  • Trans fatty acids
    • Lower HDLs and Raise LDLs
essential fatty acids
Essential Fatty Acids
  • Linoleate (GLA)
  • Linolenate
  • Arachidonic Acid is essential and may be formed from dietary linoleic acid
  • Note: Essential FAs are because we do not have enzymes to produce double bonds beyond carbon 9
  • Conjugated FA in “Organic Beef”
    • Cancer treatment?
fat storage control mechanism
Fat Storage Control Mechanism
  • Leptin System (Not well known yet)
    • Small molecular weight protein produced by white adipose tissue
    • Has numerous metabolic effects where one is in the hypothalamus----
      • Leptin with its receptor molecule suppresses food consumption by increasing the release of corticotropin-releasing hormone and suppression of something called a neuropeptide Y
lipid peroxidation
Lipid Peroxidation
  • Inhalation of high concentration of oxygen causes excessive peroxidation of unsaturated FAs
  • Polyunsaturated FA susceptible to spontaneous peroxidation (non-enzymatic)
  • Autocatalytic
  • Due to presence of oxygen and some metal ions like Fe++
  • Daisy chain effect
  • Causes membrane damage and allows for greater cytotoxicity (less selective permeability)
reducing peroxidation
Reducing Peroxidation
  • Antioxidants (Reduce oxidative damage)
    • Vitamin E (-tocopherol)
      • Functionally related to the status of—
        • Selenium
        • Vitamin C
        • Iron
        • -carotene
        • Sulfur containing amino acids
        • Overall anti-oxidant defense
reducing peroxidation selenium
Reducing Peroxidation-Selenium
  • The more the selenium, the less vitamin E is necessary
  • Selenium associated with glutathione peroxidase which is involved in free radical reduction
reducing peroxidation vitamin c
Reducing Peroxidation-Vitamin C
  • Water soluble free radical scavenger and reducing agent
  • Complements vitamin E function
    • Involved in the formation (rejuvenation) of reduced vitamin E
reducing peroxidation carotene
Reducing Peroxidation--carotene
  • Precursor to vitamin A
  • Free radical scavenger
  • Quencher of singlet oxygen
reducing peroxidation iron
Reducing Peroxidation-Iron
  • Removal of transition metal ions especially Fe++ is important in prevention of hydroxyl radicals (OH)
reducing peroxidation sulfur containing amino acids
Reducing Peroxidation-Sulfur Containing Amino Acids
  • Muscular dystrophy occurred in animal studies when fed a Vitamin E deficient diet along with lacking selenium and sulfur containing amino acids
  • Sulfur containing amino acids is necessary for the synthesis of reduced GSH
    • N-acetylcysteine
    • Methionine (SAMe)
vitamin e
Vitamin E
  • Lipid soluble
  • Collective term for

all the tocopherols and

tocotrienols

    • Difference in double

bond location

vitamin e absorption transport
Vitamin E Absorption/Transport
  • Lumen of intestine
    • Tocopherol ester hydrolyzed to free tocopherol by pancreatic lipases
  • Packaged in chylomicrons
  • Stored in liver and packaged in VLDLs
  • Transported to peripheral cells
  • Bound to a protein to facilitate transfer between membranes
    • -tocopherol transfer protein
vitamin e biological function
Vitamin E Biological Function
  • Protects membranes from oxidative damage (Anti-oxidant)
not all vitamin e s are the same
Not All Vitamin E’s Are The Same
  • Biopotency based on pharmaceutical or synthetic form of vitamin E called all-rac--tocopheryl acetate
foods rich in vitamin e
Foods Rich in Vitamin E
  • Nuts
  • Seeds
  • “Margarine”
    • Vitamin E and unsaturated fatty acids?
vitamin a and carotenoids
Vitamin A and Carotenoids
  • Fat soluble vitamin
  • Exhibit biological activity of retinol
    • Alcoholic form of Vitamin A
  • Over 530 carotenoids found in nature with less than 50 have Vitamin A activity
  • NOTE: The term “retinoids” describe retinol like compounds NOT necessarily biological activity
structure of retinoids
Structure of “Retinoids”
  • Three basic structural components
    • -ionone ring
    • Polyunsaturated chain
    • Polar end group
  • Vitamin A is stored as retinyl esters
    • Retinol esterified with long chain fatty acid
    • Loss of polar end group
not all vitamin a s are the same
Not All Vitamin A’s are the same
  • Synthetically the -ionone ring has been replaced
  • Varieties of aromatic rings are added
vitamin a absorption and metabolism
Vitamin A Absorption and Metabolism
  • Absorption of retinyl esters
    • Hydrolysis by retinyl ester hydrolase by a pancreatic and brush border membrane form of the enzyme
  • All trans form is preferred
carotenoids
Carotenoids
  • Absorbed at lower efficiency than retinol
  • May be broken down immediately
  • Or, stored in liver and adipose tissue
    • False child jaundice
  • Oxygen scavenger (Anti-oxidant itself)
storage and mobilization of vit a
Storage and Mobilization of Vit.A
  • Stored as retinyl esters
    • Esterification with long chain fatty acids that make retinol very hydrophobic and therefore accumulates into droplets
    • Esterification enzymes
      • ARAT-acyl CoA:retinol acyltransferase
      • LRAT-lecithin:retinol acyltransferase
        • Both ARAT and LRAT are membrane integrated enzymatic proteins
synthesis of retinal retinoic acid
Synthesis of Retinal & Retinoic Acid
  • Retinol may be converted to retinal
    • Dehydrogenation of retinol with electron acceptors NAD+ and NADP+
  • Retinoic acid is produced from further oxidation from retinal
    • Converted into other metabolites
    • Not known true nature of retinoic acid
    • Involved in genetic control
    • Oxidation may be involved with Cytochrome P450 (Microsomal)
retinol binding proteins
Retinol Binding Proteins
  • RBP-retinol binding protein
    • Synthesized in liver
    • Mainly a carrier of retinol in plasma
  • RBP is bound to TTR (transthyretin)
    • TTR is a carrier of thyroid hormones in blood
    • Binding of RBP to TTR prevents plasma loss of small molecular weight RBP by glomeruli filtration
food sources of vitamin a
Food Sources of Vitamin A
  • Preformed retinol
    • Liver
    • Whole and fortified milk
    • Eggs
  • Carotenoids
    • Yellow-orange vegetables and fruits
      • Carrots, sweet potato
    • Dark-green leafy vegetables
      • Spinach, broccoli
toxicity and vitamin a
Toxicity and Vitamin A
  • Toxicity associated with excessive intake
  • Retinoic acid
vitamin a deficiency
Vitamin A Deficiency
  • Rare in developed countries
  • Depressed immune function
  • Night blindness
  • Xerophthalmia (misshapen cornea)
  • Drying of conjunctiva and cornea
    • Xerosis
  • blindness
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