Chapter 10: Lipids

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Chapter 10 Lipids

• Dr. Clower
• Chem 4202

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Lipids

• One of 4 major classes of compounds found in
  living tissue
• Nucleic acids, proteins, carbohydrates, lipids
• Oils, fats, or fat-like material
• Some vitamins, hormones
• Not polymeric
• Aggregate
• Structural matrix of biological membranes
• Structural variety
• Largely hydrophobic
• Insoluble in water
• Soluble in organic solvents (chloroform, ether)

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Outline

• Storage
• Fatty acids
• Triacylglycerols
• Structural
• Phospholipids
• Glycolipids
• Sterols
• Other lipids
• Fat-soluble vitamins
• Eicosanoids

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Fatty Acids

• Simplest type components of more complex lipids
• Carboxylic acids with long aliphatic hydrocarbon
  chains
• Generally 10-20 carbons
• Most common are 16, 18
• Mostly even number due to synthesis
• Saturated or unsaturated

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Saturated Fatty Acids

• Only C-C
• Highly flexible
• Most stable conformation fully extended
• mp increase with chain length
• ex stearic acid (octadecanoic acid)

Know the names of all FAs given in this PPT
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Unsaturated Fatty Acids

• Contains C-C
• Can be polyunsaturated
• essential FAs
• First double bond typically at C9
• D9
• Double bonds every three carbons
• D9,12
• -CH-CH-CH2-CH-CH-CH2-
• ex oleic acid (181) and linoleic acid (182)

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Omega-3 Fatty Acids

• Corn, fish oil
• Reduce possibility of heart disease
• Dont stick to walls of blood vessels
• Promote blood flow
• ex linolenic acid

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Unsaturated Fatty Acids

• Double bonds
• Typically cis or trans?
• Causes bend in hydrocarbon chain
• Do not pack as well as saturated FAs
• mp decrease as unsaturation increases

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Triacylglycerols

• aka triacylglycerides
• Fatty acid triesters of glycerol
• Simple
• Mixed

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Triacylglycerols

• Most abundant class of lipids in animals
• mp determined by degree of unsaturation
• More unsaturation in plants than in animals
• Function energy reserves, insulation
• Better source of E than carbohydrates
• Stored in adipocytes throughout the body
• Hydrolyzed by lipases as needed

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Fatty acids in food

• Triacylglycerols and free FAs
• Saturated solid at rt
• Unsaturated liquid at rt
• Fat mostly saturated
• Animal sources (meat, butter)
• Oil mostly unsaturated
• Plant sources (olive, peanut)
• Partial hydrogenation
• Raise mp (semi-solid)
• Soft margarine, etc.
• More sat fat but less cholesterol than butter
• Side effect production of trans FAs
• Behave like saturated fat
• Increases LDL levels
• Decrease HDL levels

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Structural Lipids

• Amphipathic
• Hydrophobic chain(s)
• Hydrophilic (-OH or larger)
• Pack into bilayers
• Biological membranes

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Phospholipids

• Contain phosphodiester bond
• Negative charge at physiological pH
• Example Glycerophospholipids
• aka phosphoglycerides
• Major component of membranes
• Esterified glycerol-3-phosphate
• Phosphoryl group linked to polar group (various
  structure)

L is naturally occurring
D X
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Saturated C16 or C18 FA
Unsaturated C16 C20 FA
Phosphodiester linkage

• Derived from polar alcohol
• smallest H (from H-OH)
• least common in membranes
• phosphatidic acid

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Structure of Glycerophospholipids

• Determined by analysis of products from
  enzyme-catalyzed hydrolysis
• Phospholipases
• Cleave specific bonds
• Enzymes are small
• Only section being
• cleaved fits in active site
• Remainder of lipid in
• non-aqueous environment
• or stabilized by nonpolar
• AA side chains

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Plasmalogens

• One type of glycerophospholipid
• C1 linkage is a,b-unsaturated ether (not ester)
• Heart tissue of vertebrates
• Membranes of some invertebrates and bacteria

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Glycolipids

• Monosaccharide or oligosaccharide at polar end
• Example Galactolipids
• Galactose residues
• Glycosidic linkages to C3 of 1,2-diacylglycerol
• Plant cells
• Internal membranes of chloroplasts

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Sphingolipids

• Also major component of membranes
• Phospholipid or glycolipid (depends on polar
  group)
• Derivatives of sphingosine (instead of glycerol)
• C18 amino alcohol
• Ceramide
• Acylated amine
• Parent compound of most abundant sphingolipids

• Polar head group ? derivatives
• Phosphodiester or glycosididic or linkage

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Phosphate derivative structurally similar to
glycerophospholipids
Phospholipid
monosaccharide
Glycosphingolipids
neutral 2 or more sugars (Glc, Gal, or GalNac)
oligosaccharide N-acetyl neuraminic acid
negative at pH 7
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Glycerophospholipids/Sphingolipids

• Structural similarities

Back
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Sterols

• Sterol
• Four fused rings
• Greater rigidity than other membrane lipids
• One or more hydroxyl groups
• Gives amphipathic character
• Hydrocarbon side chain
• Length of C16 FA
• Cholesterol
• Most abundant sterol in animals
• Produced by liver supplied by diet
• High levels lead to gallstones and deposits on
  arteries (plaque)

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Sterols

• Metabolic precursors of steroid hormones
• Regulate physiological functions
• Androgens (testosterone)
• Estrogens (b-estradiol)
• Glucocorticoids (cortisol)
• Insoluble in water
• Bind to proteins for transport to target tissue

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Vitamin D

• Sterol derivatives
• Open B rings
• Function
• Regulate Ca and P absorption during bone growth
• Sources
• Diet D2 (milk additive, plant sources) and D3
  (animal sources)
• Precursor intermediate in cholesterol synthesis
• Formed in skin non-enzymatically from
  7-dehydrocholesterol
• Deficiency
• Soft bones, impaired growth and skeletal
  deformities in children

Inactive form
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Other Lipids

• Classified on basis of physical properties
• Solubility
• Hydrophobicity
• Amphiphilicity
• Fat-soluble vitamins
• Vitamins A, E, K (and D)
• Isoprenoids
• Eicosanoids
• Prostaglandins
• Thromboxanes
• Leukotrienes

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Vitamin A

• Collective term for retinol, retinal, retinoic
  acid
• Formed from oxidative cleavage of b-carotene in
  liver
• Function
• Aldehyde visual cycle/process, component of
  rhodopsin (visual pigment)
• Alcohol, carb acid growth, reproduction
• Deficiency
• Night blindness
• Xerophthalmia
• Dryness in eyes
• No tear production
• Damage to cornea
• Leads to blindness

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Vitamin K

• Phylloquinone or menaquinone
• Function
• Synthesis of blood clotting proteins
• Sources
• K1 plants K2 animals
• Bacteria in intestine
• Deficiency
• Unlikely due to synthesis and wide distribution
  in food
• Injection for infants
• Hemolytic anemia destruction of red blood cells
• Toxicity
• Jaundice from large doses of vit. K, toxic
  effects on membrane of red blood cells, cells
  die, lead to increased levels of yellow bilirubin
  (formed from heme)

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Vitamin E

• a-tocopherol
• Function
• Antioxidant prevents cell damage from oxidation
  of polyunsaturated FAs in membranes by O2 and
  free radicals
• Deficiency
• Associated with defective lipid
  transport/absorption

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Olestra

• Artificial, noncaloric fat substitute
  (indigestible)
• FDA warning
• This Product Contains Olestra. Olestra may cause
  abdominal cramping and loose stools. Olestra
  inhibits the absorption of some vitamins and
  other nutrients. Vitamins A, D, E, and K have
  been added.

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Eicosanoids

• Hormones involved in production of pain, fever,
  inflammatory reactions
• Prostaglandins
• Thromboxanes
• Leukotrienes
• Metabolites of arachidonic acid (a
  polyunsatruated FA)
• Synthesis inhibited by NSAIDs
• e.g. acetylsalicylic acid (aspirin)
• Acylate Ser residue, preventing access to active
  site

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Chapter 10 Problems

• 1-5, 8-10