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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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Medical biochemistry robert f waters phd

Medical BiochemistryRobert F. Waters, PhD

Lipid Overview

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


    • 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


  • 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