sept 9 bt202
TRANSCRIPT
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BT-202Netaji Subhas Institute of Technology,
Dwarka, New Delhi.Dr. Amita Pandey
Sept 9, 2011
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Types of Lipids
• Lipids with fatty acidsWaxesFats and oils (triglycerides)PhospholipidsSphingolipids
• Lipids without fatty acidsSteroids
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STORAGE LIPIDS
• Fatty acids• Triglycerides
-hydrocarbon chain with a carboxylic acid at one end.
A 16-C fatty acid: CH3(CH2)14-COO-
Non-polar polar
-most naturally occurring fatty acids have an even number of carbon atoms.
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FATTY ACIDS
-Saturated FAs-Unsaturated FAs
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FATTY ACIDS
-high melting point-poor solubility in water
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FATTY ACIDS
-Low melting points-Occur in cis form
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-poor solubility is due to long non-polar HC chains
-melting point is due to the degree of packing of FAs
-FAs are present in blood intwo forms
-serum albumin-esters or amides
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PUFAs
• The double bond is at the methyl end of the HC chain.
• This carbon is called omega carbon
• Two most important PUFAs are– Omega -3- fatty acids – Omega-6-fatty acids
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PUFAs and cardiovascular disease
• Imbalance between omega-6 and omega-3 PUFAs (Optimum ratio is 1:1 to 4:1)
• Humans cannot synthesize omega-3 (α-linolenic acid, ALA; 18:3 (Δ9,12,15)
• ALA is used for synthsesis of two other important PUFAs i.e. EPA and DHA
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Properties of SaturatedFatty Acids
• Contain only single C–C bonds
• Closely packed
• Strong attractions between chains
• High melting points
• Solids at room temperature
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Properties of UnsaturatedFatty Acids
Contain one or more double C=C bondsNonlinear chains do not allow molecules to pack closelyFew interactions between chainsLow melting pointsLiquids at room temperature
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Triacylglycerols / Triglycerides
-three FA molecules linked to one glycerol molecule
-two types of triacylglycerols-simple (eg. tripalmitin)-mixed
-hydrophobic molecules
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Triacylglycerols
• Stored energy -adipocytes in vertebrates-seeds in plants
• Insulation
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Trans Fatty Acids
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Trans Fatty Acids
CH
CH2
CH2 O
O
O
C
O
(CH2)5CH CH(CH2)7CH3
C
O
(CH2)5CH CH(CH2)7CH3
C
O
+
(CH2)5CH CH(CH2)7CH3
H23Ni
CH
CH2
CH2 O
O
O
C (CH2)14CH3
O
C (CH2)14CH3
O
C (CH2)14CH3
O
-Hydrogenation converts double bonds in oils to single bonds.
-helps improve stability of oils during frying
-increase shelf life
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Trans Fatty Acids
-partial hydrogenation also converts the cis-double bond to trans double bonds
-trans fatty acids increase the risk of coronary heart disease
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Waxes
• Composed of FA molecules linked to long-chain alcohol
molecule through an ester linkage
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LIPIDS
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Structural LIpids
• Phosphoplipids
• Glycolipids –Glycerophospholipids
• Archeal ether lipids -Sphingolipids
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Glycerophospholipids/Phosphoglycerides
• They have a glycerol backbone.
• Hydroxyls at C1 & C2 are esterified to fatty acids
• C3 hydroxyl is esterified to phosphate
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Glycerophospholipids/Phosphoglycerides
• Parent compound is phosphatidic acid where the X is hydrogen atom
• The 2 fatty acids tend to be non-identical.
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Glycerophospholipids/Phosphoglycerides
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Glycerophospholipids/Phosphoglycerides
Phosphatidylinositol, with inositol as polar head group, -a membrane lipid
-has roles in cell signaling.
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Glycerophospholipids/Phosphoglycerides
Phosphatidylcholine, with choline as polar head group is a common membrane lipid.
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Glycerophospholipids/Phosphoglycerides
Ether lipids
-plasmalogen
-platelet-activatingfactor
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Galactolipids/Sulfolipid
• Found in membranes of plant cells
• Thylakoid membrane
• sulfolipid
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Archaeal ether lipids
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Sphingolipids
• Are derived from lipid Sphingosine
• The amino group of sphingosine can form an amide bond with a fatty acid carboxyl, to yield a ceramide.
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Sphingolipids
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Sphingolipids
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Sphingomyelin
•a phosphocholine or phosphethanolamine head group.
•Found in myelin sheath
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Glycosphingolipid
• Cerebrosides-present on the outer
surface of PM-head group attached
to sugar-no phosphate-galactose (neural)-glucose (non neural)
• Globosides-more than one sugar(D-glucose, D-galactose)
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Gangliosides
• Oligosacharides as their polar head group• Have Neu5Ac also called sialic acid at termini• Negatively charged• GM, GD, GT, or GQ
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Function of Sphingolipids
• Present in PM of neurons• Act as recognition sites on
the celleg., recognition of blood type
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• Phopholipases• Lysophopholipases
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Sterols
• Cholesterol in animals
• Stigmasterol in plants
• Ergasterol in fungi• Act as precursors
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LIPIDS IN THE CELL
• Lipids exist in cells as-plasma lipoproteins-plasma membrane
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LIPOPROTEINS
-complexes of lipids and proteins-are water solubleChylomicrons: 99% lipids. Involved in transportation of triglycerides absorbed in the intestine to liver, skeletal muscles and adipose tissue
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• Very Low Density Lipoproein (VLDL):90% lipids. Transport of triglycerides synthesized in
the liver to adipose tissue
• Intermediate density Lipoproteins (IDL):not detectable in blood
• Low Density Lipoprotein: 78% lipids. Transport of cholesterol (mostly as acyl
esters), synthesized in the liver.
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• High Density Lipoproteins:50% lipids. Transport of cholesterol from tissues to
liver for catabolism.
Lipoprotein lipases
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LIPIDS AND BIOLOGICAL MEMBRANES
Lipid bilayerVesicles
-Liposomes-Bangosomes
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Lipid composition of plasma membraneand organelle membrane of rat hepatocytes
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Fluid Mosaic Model
S. J. Singer and G. L. Nicolson (1972) proposed the fluid mosaic model for membrane structure, which suggested that membranes are dynamic structures composed of proteins and phospholipids.
-Lipids are assymetrically distributed
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-Peripheral protein (Extrinsic protein)
-Integral protein (Intrinsic proteins)
-Amphitropic proteins
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• Integral membrane proteins and Lipids-hydrophobic residues span the membrane (α-helical)-Tyr and Trp residues are present-positive inside rule (Lys, His , and Arg)
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Hydropathy Index
-Determination of protein conformation-sequence of 20 hydrophobic residues
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Lipid-linked membrane proteins
-lipid anchors-ionic attractions
inside outside
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Movement of lipids in the bilayer
• Uncatalyzed • Catalyzed
FlippasesFloppasesScramblases
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Transport across membrane
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Solute concentrationElectrical potential
Simple diffusion
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Facilitated diffusion
• Transporters or permeases
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Classification of transporters
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Carriers-bind to substrate with high stereospecificity-transport rates are slow-are saturable
Channels-less stereospecific-faster than carriers-oligomeric proteins
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• GLUT 1-12:-Transports glucose out of liver cells upon glycogen metabolism
• Chloride-bicarbonate exchanger-anion exchange (AE) protein-increases the rate of HCO-
3 transport across erythrocyte membrane
• Three general classes of transport system
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Active transport
P-type ATPases:-Reversible phosphorylated by ATP-cation transporters-membrane proteins with 8-10 membrane spanning regions-Ca2+ ATPases and Na+K+ ATPases-bacteria pump out toxic heavy metal ions such as Cd2+ and Cu2+
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SERCA pump Na+ K+ ATPase
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F-Type ATPases-Catalyze the passage of protons by ATP hydrolysis-transport can occur in either direction -also called ATP synthases as in mitochondria and chloroplast-FoF1 ATPase in bacteria and AoA1 ATPases in Archaea
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V-type ATPases
-responsible for maintaining acidic pH in vacuoles, lysosomes, endosomes, golgi complex and secretory vesicles
-two domains Vo (integral domain) and V1 (peripheral domain)
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ABC Transporters
-ATP dependent transporters-transport amino acids, peptides, proteins, metal ions, lipids, bile salts and also drugs-MDRI also called multi-drug transporter in humans
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Secondary Active Transport
-Major facilitator superfamily (MFS)-12 transmembrane domains-lactose transporter of E. coli.-Na+-glucose symporters
Lactose permease
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AQUAPORINS (AQPs)
-secretion of sweat, saliva, and tears occur through AQPs
-Arabidopsis has 38 AQPs
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Ion-selective channels
-rate of flux through the channels is several orders of magnitude greater than transporters – 107 to 108 /sec
-not saturable
-have a gated response-ligand-gated-voltage-gated
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K+ ion channel
Na+-ion channel (voltage gated)Nicotinic acetylcholine receptor (ligand gated)GABA receptors
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