Biological Lipids and Bilayers

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Biological Lipids and Bilayers

• Lipids are nearly insoluble in Water
• Form Biological membranes
• Regulate solute flow and signalling
• Provide concentrated energy stores
• Structure, Classification and Nomenclature
• Fatty acids, polar headgroups, steroids and
  eicosanoids
• Lipid Bilayers
• Micelles, bilayers and vesicles
• Fluidity

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Fatty Acids

• Carboxylic Acid at C1
• Acyl chain
• Usually 14 - 20 carbons (including C1)
• Usually even -- built from C2 (acetyl) units
• Saturated (no double bonds)
• Strong interactions between parallel acyl chains
  High MP.
• UnSaturated (double bonds)
• Almost always cis, Often at C9
• Weak interactions between parallel acyl chains
  Low MP.
• Polyunsaturated
• Usually not conjugated

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Triacylglycerols

• Storage form of fatty acids
• Charges neutralized
• Fatty acids added or removed one at a time

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Glycerophospholipids

• The simplest Glycerophospholipid is phosphatidic
  acid
• 1, 2 diacyl glycerol with a phosphate on C3
• Phosphatidyl ethanolamine bears a phospho
  ethanolamine at C3
• Similarly phosphatidyl
• Choline
• Serine
• Inositol

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Cardiolipipins

• Phosphatidyl glycerol contains a second glycerol
  head group
• Cardiolipins have 2 glycerols connected by a
  single phosphate and 4 acyl chains

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Phospholipases

• Cleave ester linkages in phospholipids
• Phospholipase A1
• fatty acyl chain 1
• Phospholipase A2
• fatty acyl chain 2
• Phospholipase C
• Glycerol - phosphate
• Phospholipase D
• Phosphate - inositol

A1
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Plasmalogens

• Have an a, b unsaturated ether in place of the
  ester at C1 in a glycerophospholipid
• Most common head groups are phosphoserine ,
  phosphocholine and phosphoethanolamine

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Sphingolipids

• Sphingosine is an 18 Carbon amino alcohol
• Ceramides are N-Acyl fatty acid derivatives of
  sphingosine
• Sphingomyelins are sphingophospholipids that bear
  phosphoethanolamine or phosphocholine head groups

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GlycoSphingolipids

• Carbohydrates linked via simple ester linkage to
  the primary alcohol of ceramide
• Glycosphingolipids are extracellular
• Concentrated in Neural membranes
• Cerebrosides have 1 sugar
• Usually glucose or mannose
• Gangliosides
• have oligosaccharides

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Steroids

• Cholesterol stiffens membranes
• can be fatty acylated
• Steroid hormones are lipid soluble
• Receptors are cytoplasmic

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Steroid Hormones

• Glucocorticoids
• Regulate metabolism and inflammation
• Mineralocorticoids
• Regulate Salt and Osmotic balance in Kidney
• Androgens - Male hormones
• Estrogens - Female hormones
• Vitamin D derivatives
• UV light can cleave C9-C10
• Regulates Ca2 metabolism esp bone growth and
  repair

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Eicosanoids

• C20 Fatty acids
• membrane localized, short term signalling
  molecules
• Precursor is arachidonic acid
• 5,8,11,14, Eicosatetraeneoic acid
• Prostaglandins
• Pain and fever
• Prostacyclins
• Stimulate vasodilation, free flow of blood
• Thromboxanes
• Stimulate vasoconstriction, clotting
• Leukotrienes
• Inflammation, asthma

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Arachidonic Acid Metabolites

• ProstaglandinH2 is a precursor to
• Prostaglandins
• Prostacyclins
• Thromboxanes
• PGH2 synthase inibited by aspirin, acetominophen
  and ibuprophen

PGH2 synthase