Lipids

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Lipids
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Lipids

• Defined on the basis of solubility.
• Lipid- water insoluble organic substance
  extractable by nonpolar solvents, typically
  chloroform or ether.
• Many distinct chemical species in a lipid
  fraction

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Functions of Lipids

• 1. Energy storage source for animals
• 2. Structural elements (plasma membrane) of
  cells and organelles
• 3. Signal transduction molecules
• 4. Sleep-inducing lipids recently identified

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Classification of Lipids

• 1. Open chain compounds (saponifiable)
• a. Fatty acids
• b. Triglycerides
• c. Phospholipids
• d. Sphingolipids
• e. Waxes
• 2. Closed chain (non-saponifiable)
• a. Cholesterol
• b. Steroids
• 3. Derived

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1a. Fatty Acids

• Not found free.
• Present in triglycerides
• Present in phospholipids
• Even number of carbon atoms (exceptions).
• Unbranched (exceptions).
• Saturated or unsaturated (only cis)
• 16- and 18-C long are most abundant.
• Numbered from carboxyl end

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Saturated Fatty Acids

• Palmitic (160)
• Stearic (180)

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Unsaturated Fatty Acids

• Palmitoleic (161D9)
• Oleic (181D9)

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Essential Fatty Acids

• Linoleic (182D9,12) w6
• Linolenic (183D9,12,15) w3
• Arachidonic (204D5,8,11,14) w6
• omega (w) 3 or n-3 are other common
  designations

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Properties and Reactions of Fatty Acids

• Saturated vs. Unsaturated
• melting point (2 factors)
• iodine number
• Carboxylic acid leads to ester

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1b. Triacylglycerols

• Triesters of glycerol and 3 fatty acids
• store a lot of energy- do not function as
  structural elements
• Lipases act when we need energy

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1c. Phosphoacylglycerols

• The 3 C of glycerol has a head group attached
  through a phosphate ester
• PA
• PC
• PS
• PE
• PI

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1d. Sphingolipids

• Sphingosine instead of glycerol
• amide linkage
• nomenclature gets ugly real fast

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2. Steroids

• know cholesterol
• conversion

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3. Derived Lipids

• 1. Fat-soluble vitamins (recognize)
• 2. Prostaglandins, Thromboxanes and Leukotrienes
• 3. Isoprenoids

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Vitamin A (Retinol)

• Derived from ß-carotene
• Oxidized to retinal
• Functions in vision cycle
• Deficiency Night blindness
• Excess bone pain

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Vitamin D

• Metabolism helps remember structure
• Functions in calcium metabolism
• Deficiency rickets in children
• Excess lumpy bones, kidney stones

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Vitamin E

• Functions as antioxidant
• Deficiency not known
• Excess blurred vision and headache

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Vitamin K

• Different forms, most common n8
• Functions in blood clotting by unknown means
• Deficiency blood clotting
• Excess hemolytic anemia

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PG, TX, and LT

• Common structural feature of the three classes

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Isoprene

• Can polymerize
• reason for branched chains on numerous examples

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Lipid Solubility

• Amphipathic- hydrophilic and hydrophobic regions
• Possible arrangements
• monolayer
• micelle
• bilayer

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All Membranes are Different

• 5-10 nm thick
• Protein and lipid 11
• PC and PE predominate
• curved Assymetric
• fluidity varies with temperature and composition

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Singers Fluid Mosaic Model

• peripheral and integral membrane proteins
• lateral fluidity of lipid and protein
• flip-flop is rare
• membrane fusion is constant

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Membrane Transport

• 1. Diffusion
• down concentration gradient
• no energy
• extremely slow
• 2. Facilitated Diffusion
• 3. Active transport (primary)
• 4. Active transport (secondary)
• 5. Endocytosis/RME
• channels and receptors changing membranes