Sept 9 bt202

BT-202Netaji Subhas Institute of Technology,

Dwarka, New Delhi.Dr. Amita Pandey

Sept 9, 2011

Types of Lipids

• Lipids with fatty acidsWaxesFats and oils (triglycerides)PhospholipidsSphingolipids

• Lipids without fatty acidsSteroids

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.

FATTY ACIDS

-Saturated FAs-Unsaturated FAs

FATTY ACIDS

-high melting point-poor solubility in water

FATTY ACIDS

-Low melting points-Occur in cis form

-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

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

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

Properties of SaturatedFatty Acids

• Contain only single C–C bonds

• Closely packed

• Strong attractions between chains

• High melting points

• Solids at room temperature

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

Triacylglycerols / Triglycerides

-three FA molecules linked to one glycerol molecule

-two types of triacylglycerols-simple (eg. tripalmitin)-mixed

-hydrophobic molecules

Triacylglycerols

• Stored energy -adipocytes in vertebrates-seeds in plants

• Insulation

Trans Fatty Acids

Trans Fatty Acids

CH

CH2

CH2 O

O

O

C

O

(CH2)5CH CH(CH2)7CH3

C

O


C

O

+


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

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

Waxes

• Composed of FA molecules linked to long-chain alcohol

molecule through an ester linkage

LIPIDS

Structural LIpids

• Phosphoplipids

• Glycolipids –Glycerophospholipids

• Archeal ether lipids -Sphingolipids

Glycerophospholipids/Phosphoglycerides

• They have a glycerol backbone.

• Hydroxyls at C1 & C2 are esterified to fatty acids

• C3 hydroxyl is esterified to phosphate


• Parent compound is phosphatidic acid where the X is hydrogen atom

• The 2 fatty acids tend to be non-identical.


Phosphatidylinositol, with inositol as polar head group, -a membrane lipid

-has roles in cell signaling.


Phosphatidylcholine, with choline as polar head group is a common membrane lipid.


Ether lipids

-plasmalogen

-platelet-activatingfactor

Galactolipids/Sulfolipid

• Found in membranes of plant cells

• Thylakoid membrane

• sulfolipid

Archaeal ether lipids

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.

Sphingolipids

Sphingomyelin

•a phosphocholine or phosphethanolamine head group.

•Found in myelin sheath

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)

Gangliosides

• Oligosacharides as their polar head group• Have Neu5Ac also called sialic acid at termini• Negatively charged• GM, GD, GT, or GQ

Function of Sphingolipids

• Present in PM of neurons• Act as recognition sites on

the celleg., recognition of blood type

• Phopholipases• Lysophopholipases

Sterols

• Cholesterol in animals

• Stigmasterol in plants

• Ergasterol in fungi• Act as precursors

LIPIDS IN THE CELL

• Lipids exist in cells as-plasma lipoproteins-plasma membrane

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

• 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.

• High Density Lipoproteins:50% lipids. Transport of cholesterol from tissues to

liver for catabolism.

Lipoprotein lipases

LIPIDS AND BIOLOGICAL MEMBRANES

Lipid bilayerVesicles

-Liposomes-Bangosomes

Lipid composition of plasma membraneand organelle membrane of rat hepatocytes

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

-Peripheral protein (Extrinsic protein)

-Integral protein (Intrinsic proteins)

-Amphitropic proteins

• 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)

Hydropathy Index

-Determination of protein conformation-sequence of 20 hydrophobic residues

Lipid-linked membrane proteins

-lipid anchors-ionic attractions

inside outside

Movement of lipids in the bilayer

• Uncatalyzed • Catalyzed

FlippasesFloppasesScramblases

Transport across membrane

Solute concentrationElectrical potential

Simple diffusion

Facilitated diffusion

• Transporters or permeases

Classification of transporters

Carriers-bind to substrate with high stereospecificity-transport rates are slow-are saturable

Channels-less stereospecific-faster than carriers-oligomeric proteins

• 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

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+

SERCA pump Na+ K+ ATPase

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

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)

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

Secondary Active Transport

-Major facilitator superfamily (MFS)-12 transmembrane domains-lactose transporter of E. coli.-Na+-glucose symporters

Lactose permease

AQUAPORINS (AQPs)

-secretion of sweat, saliva, and tears occur through AQPs

-Arabidopsis has 38 AQPs

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

K+ ion channel

Na+-ion channel (voltage gated)Nicotinic acetylcholine receptor (ligand gated)GABA receptors

Sept 9 bt202

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