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Lipoproteinsandlipidtransport

AtifH.Khirelsied,B.Sc,M.Sc,Ph.D.

Departmentof

Biochemistry

FacultyofMedicineandHealthSciences

InternationalUniversityofAfrica,Khartoum,Sudan

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Lipoproteinsstructure

cholesteryl esters)

Apolipoproteins onthesurface

large:apoB (b

48

and

B

100)

atherogenic

, ,

C assi ie ont e asiso ensityan e ectrop oretic

mobility(VLDL;LDL;HDL)

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Compositionandphysicalpropertiesofhuman

li o roteins

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Lipoproteinsstructure

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Theapolipoproteins

Essentialcomponentsoflipoproteins.

Oftenreferredtoasapoproteins

Classifiedby

alphabetical

designation

(A

thru

E)

Responsibleforrecognitionofparticlebyreceptors.

Somehavecatalyticorcoenzymeactivity.

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Apoproteins ofhumanlipoproteins

AI(28,300) principalproteininHDL

90120mg%inplasma;activatesLCAT

AII(8,700) occursasdimer mainlyinHDL

30 50mg%;enhanceshepaticlipaseactivity

B48 (240,000) foundonlyinchylomicron

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Pro ertiesofthema orclassesofa oli o roteins

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Electrophorogram ofplasmaproteins

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Chylomicrons

Formedinthemucosalcellsintheintestine.

suclavian veins.

Degradedto

remnants

by

the

action

of

lipoprotein

cellsurface

Remnantsaretakenupbyliverparenchymal cellsdue

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Dietarycholesterolisabsorbedasesterandtransportedin

ch lomicrons

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Thechylomicrons

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Transferofapoproteins fromHDLtochylomicrons

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VeryLowDensityLipoprotein(VLDL)

ascent st en nteractw t togenerate

mature

VLDLs

(with

added

cholesterol,

apoC

II

and

ature

s

are

acte

upon

y

p to

generate

VLDLremnants(IDL)

IDL

are

further

degraded

by

hepatic

triglyceride

pase togenerate s

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ThefateofVLDL

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LDLreceptor

Receptora soca e B Ereceptor ecauseo itsabilitytorecognizeparticlescontainingbothapos B

,

B100/apo

E

binding

Theintracellulardomainisresponsibleforclustering

membrane

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Cholesteroluptakeby

receptormediated

endocytosis.

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HighDensityLipoproteins(HDL)

Severalsubfamiliesexist

.

Itinteractswithchylomicron remnantsand

lecithincholesterol

acyl transferase

(LCAT)

to

form

HDL3

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ThefunctionofHDL

Trans ersproteinstoot er ipoproteins

Picksupcholesterolfromcellmembranes

ConvertscholesteroltocholesterolestersviatheLCAT

reaction

ransportc o estero esterstot e ver re erre toas

reversecholesteroltrans ort

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ThefateofHDL

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Thelecithincholesteryl acyl transferase (LCAT)

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Thelecithincholesteryl acyl transferase (LCAT)

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ReversecholesteroltransportbyHDL

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Thefunctionof CETP

Thecholesterolestertransfer

protein(CETP).

CETPtransferscholesterolesters

rom o nexc ange

fortriacylglycerol (TG)

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Atherosclerosis

Hardeningofthearteriesduetothedepositionof

Heartdiseaseistheleadingcauseofdeath

Causedby

the

deposition

of

cholesteryl esters

on

the

Atherosclerosis

is

correlated

with

hi h

LDL

and

low

HDL

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Atherosclerosis

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Factorspromotingelevatedbloodlipids

age

men>45yearsofage;women>55yearsofage

smoking

h ertension>140 90mmH

lowHDL

cholesterol

obesity>30%overweight

diabetesmellitus

inactivity/lackofexercise

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Optimalanddesirable levelsofserumcholesterolandLDL

cholesterol

concentrations

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