Lipids & Lipoproteins

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    Lipids & Lipoproteins

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    • Lipids are a diverse group of compounds

    that have many biological functions

    • They have 2 primary purposes in living Organisms – Storage of excess caloreis

    • Composed mostly of carbon hydrogen (rich source

    of energy

     – Structural role! "ntegral part of cell membrane

    • #ecause of their uni$ue structural design

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    Lipids

    • The term lipid applies to a class of compounds that aresoluble in organic solvents and nearly insoluble in%ater 

    • Some lipids contain non lipid groups (phosphoryl&amino& sulfate

    • They are carried in the body by lipoproteins –  Lipoproteins allo% fat to be dissolved into the plasma

    • Subdivided into ' main groups based on their chemicalstructure

    • atty acids• Cholesterol

    • Triglycerides

    • )hospholipids

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    Fatty Acids

    • Linear chains of carbon and hydrogen

     – Terminate in *COO+ carboxyl group

     – Short chain , '*- carbons

     – .edium , -*/2 carbons

     – Long chain 0 /2 carbons

    • 1iet is mostly long chains %ith even number

    of carbons

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    Fatty Acids

    • Saturated , no carbon double* bonds

    • .onounsaturated 3 / C,Cdouble bond

    • )olyunsaturated 3 0 2 C,Cdouble bonds

    • C,C causes bend (4in4 inmolecule

     –  "ncreases space needed %hencompacted

     –  .ore fluid or li$uid 3 oils at roomtemp

    Lauric acid (12:0)

    α

    β

    ωOH

    O

    OH

    O

    Palmitoleic acid (16:1)

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    Clinical importance of fatty acids

    • ecal fatty acids are sometimes measured todetect malabsorptive and pancreatic

    disorders5the test is mostly consideredobsolete

    • Serum free fatty acids help distinguish bet%een hyperinsulinemic hypoglycemia

    ( normal and disorders of fatty acidoxidation ( elevated and negative4etones

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    Triglycerides

    • 6lycerol bac4bone %ith attached by ester bonds

    • 7ach can be different

    • Triglycerides %ith saturated (no 4in4s

     –   pac4 tightly 3 solid at room tempt

    • Triglycerides %ith unsaturated typically oils at room temp

    H

    CH OH

    C

    C

    H OH

    H

    H OH

    Glycerol

    H

    CH O

    C

    C

    H   O

    H

    H   O

    CO

    CO

    CO   (CH2)n

    (CH2)n

    (CH2)n

    CH3

    CH3

    CH3

    Triglyceride

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    Triglycerides

    • .ost plant*derived are highlyunsaturated

     – Corn& safflo%er& sunflo%er& and peanut oils• .ost animal*derived saturated

     – 8sually solid at room temp

    • Triglycerides 3 9o charged groups or polarhydrophilic groups – +ydrophobic

     –  9ot soluble in %ater 

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    Triglycerides

    • Source of Triglycerides! –  7xogenous source! 1ietary

     –  7ndogenous ! Liver and tissue storage

    • Triglycerides transported by Chylomicrons(exogenous and :L1L (endogenous

    • 7nergy source %hen plasma glucose is decreased

    • Triglycerides catabolism is regulated by! –  lipase&

     –  7pinephrine&

     –  and cortisol

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    Phospholipids

    • Similar in structure totriglycerides

    • T%o – usually /' * 2' C

    long –  One saturated; one unsaturated

    • Third spot has phospholipidhead group

    • Several types of phospholipid head groups –  Choline& serine& ethanolamine&

    inositol

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    Phospholipids

    • )hosphatidylcholine –  +ave a choline head group

     –  .ost common in lipoproteins and cellmembranes

    • )hospholipids are mphipathic lipidmolecules –  +ydrophobic and hydrophilic head group

    • "n Cell membrane

     –  )olar hydrophilic faces out%ard to%arda$ueous environment

     –  +ydrophobic face in%ard a%ay from%ater 

    http://science9.files.wordpress.com/2007/04/bilayer.jpg

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    Cholesterol

    • 8nsaturated steroid alcohol * amphipathic

    • ' ring structures (& #& C& 1 %ith single side <

    chain (li4e • +ydrophilic O+ on ring

    • ' rings and side chain internal& O+ external

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    Cholesterol

    • )rimarily animal source

     –  )lants have other sterols

    • Cholesterol not used as fuel source –  9ot readily cataboli=ed by cells

    • Converted by liver to bile salts

     –  )romote fat absorption in bo%el

    • Converted to steroid hormones

     –  :itamin 1>

    • Transported by +1L and L1L

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    Cholesteryl Ester

    • +ydroxyl group bonded to

    • Therefore no polar group 3 very

    hydrophobic• 6enerally found in center of lipid droplets

    %ith triglycerides

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    Triglycerides &

    cholesteryl esters

    Lipoproteins

    • Lipids need to be transported totissues and organs to performtheir metabolic functions

    • Triglycerides ? cholesteryl estersare hydrophobic

    • There should be a form ofhydrophilic compound

    • Lipids are transported by a seriesof micelles called lipoproteins

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    Lipoproteins

    • Si=e correlates to lipid content

    • Larger particles have more lipid core – 

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    Lipoproteins

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    polipoproteins

    • polipoproteins primarily on surface oflipoprotein particle

     – .aintain structural integrity – recognition of cell surface receptors

     – ctivators ? inhibitors of various en=ymes thatmodify lipoprotein particles

     – mphipathic helix• +ydrophobic aa residues interact %ith lipids

    • +ydrophilic aa resides interact %ith a$ueousenvironment

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    Apolipoproteins

    • po */• maAor protein of +1L

    • po #• )rimary protein of L1L& :L1L and chylomicrons

    • po C• Chylomicrons& :L1L& +1L

    • po 7• L1L& :L1L& +1L

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    Chylomicrons

    • Contain apo #*'B lipoprotein

    • Largest and least dense – up to /[email protected]@nm

    • Large si=e reflect light – post*prandialserum turbidity

    • loat to the top – creamD layer 

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    Chylomicrons

    • )roduced by intestine& %here

    they are pac4aged %ith lipids

    • Triglycerides and cholesterol

    esters hydroly=ed by lipases• Leaves chylomicron remnant 3

    liver recycled

    • Therefore primary purpose istransport of dietary lipid to liver

    and peripheral cells

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    VLDL

    • Contains apo #*/@@& apo 7& po C

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    LDL

    • Contain apo #*/@@ and apo 7

    • .ore cholesterol rich

    • orm from lipolysis of :L1L

    • L1L ta4en up by cells through receptor 

     – )art of reason behind atherosclerosis

    • 8p to B subclasses – still %or4ing on

    diagnostic significance

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    LDL

    • Significantly smaller than :L1L – can

    embed in vessel %alls

    • Oxidi=ed& ta4en up by macrophages• .acrophages %ith too much lipid become

    foam cells

    • #ecome fatty strea4s – precursor ofatherosclerotic pla$ues

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    Lipoprotein (a)

    • L1L*li4e molecule

    • Contain apo (a lin4ed to apo #*/@@

    • :ery heterogeneous number of peptidese$uences (4ringles in apo (a portion

    • 7levated Lp (a increased ris4 for premature

    coronary heart disease – Eringle regions homology %ith plasminogen

     – Compete %ith binding – increase clotting

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    HDL

    • Smallest and most dense

    • Synthesi=ed by liver and intestine

    • 1iscoidal +1L has 2 apo *" molecules – orms a ring around phospholipids ?

    cholesterol

     –  9ascentFne%ly secreted +1L – active inremoval of excess cholesterol from peripheral

    cells

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    HDL

    • 1iscoidal +1L ac$uires additional lipids&

    cholesterol esters ? triglycerides form core

    region , spherical +1L• Spherical +1L predominate in plasma

    • +1L transport lipids bac4 to the liver from

     peripheral tissues