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Lipids

a) Structure & Function

b) Fat Content & Composition of Common Foods

c) Fatty Acid Metabolism

desaturation & elongation

enzymes

characteristics

sources

biological roles of prostaglandins & thromboxanes

essential fatty aicd deficiency

dietary fat type and membrane lipid composition

d) Lipoproteins

classification

functions

roles of apoproteins

hyperlipidemia

e) Cholesterol

synthesis & regulation

bile acids

enterohepatic circulation

lipoprotein receptors

Cholestyramine

f) Perspective

Lipids & Cholesterol

Are they bad to your heath?

BUT, you do need them!!!

Fatty acids:

As components of membranes

As precursors of autocrines/paracrines

prostaglandins

leukotrienes

Provides membrane fluidity (PUFA)

As energy

Essential fatty acids

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Nelson & Cox, Lehninger Principles of Biochemistry, 3rd ed., 2000

Principal classes of storage and membrane lipids

(Glycerol)

(Fatty acids)

Lipid bilayer of cell membrane

(DAG phosphate)

All glycerophospholipids contain or are derivatives of

phosphatidic acid (PA). It is the simplest phosphoglyceride and is

the precursor of other members of this group.

Sphingolipids has a sphingosine backbone (instead

of glycerol) which is an amino alcohol.

When a long-chain fatty acid is attached t the amino

group through an amide linkage, the product is

ceramide. Myelin is the only significant

sphingophospholipid in human.

Ceramide is a waxy bioactive lipid implicated in

many physiological functions including apoptosis,

cell growth arrest, differentiation, cell senescence,

and adhesion, etc.

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www.biochem.arizona.edu/.../LIPIDS/Lipids.html

Phosphatidylcholine (lecithin 卵磷脂)

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18-Carbon Fatty acids (Saturated and mono-unsaturated)

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www.hidden-diabetes-cures.com/fats-and-oils.htm

18-Carbon fatty acids

Desaturation & Elongation

18:1n9 / 18∆9

18:2n6 / 18∆9,12

18:3n3/ 18∆9,12,15

Omega (w) end

http://www.hidden-diabetes-cures.com/fats-and-oils.htm

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Canola

http://journeytoforever.org/biofuel_library/chemoils.html

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Recommended fat intake as percentage of daily energy intake

< 30% overall

< 7 -10% from saturated + trans fatty acids

~ 10% from monounsaturated fatty acids (MUFA)

~ 10% from polyunsaturated fatty acids (PUFA)

Dietary fats and oils

•Energy contribution between 20 to 40%

•Mainly in form of triacyglycerol (triglyceride)

•Intake of phospholipids (PL) is ~ 5 g

•Efficiency of digestion averages 95%

Fat digestion, absorption and resynthesis in the intestine •Lingual & gastric lipase – preferentially hydrolyze the sn3-ester bond,

forming sn1,2-DAGs.

•Pancreatic lipase – major digestive enzyme which targets fatty acids located

in the sn1/3- positions, leading sn2-MAGs as digestive products (& FFA).

•Cystic fibrosis – hereditary pancreatic deficiency

•Orlistat (XenicalR) – gastric and pancreatic lipase inhibitor is used as an

antiobesity drug because it will decrease fat digestion (absorption) and

unabsorbed fat pass out in the stool (fatty stool).

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Digestion of dietary lipids Lippincott’s Illustrated Reviews: Biochemistry, 2011

Both are available as oral

supplement (source of choline)

Pro Nutr Soc 64:205-212, 2005

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Positional distribution of fatty acids in dietary triacylglycerol

Cocoa butter mostly SOS

•Free 16:0 (palmitic acid) and 18:0 (stearic acid) have low coefficients of

absorption because of melting points above body temperature and their ability

to form calcium soaps.

•Fecal excretion of 16:0 is greatest in diets with high 16:0 at the sn-1,3

positions (native palm).

•Due to the concern over partially hydrogenated fats containing trans

fatty acids, CHEMICAL INTERESTERIFICATION has gain

popularity.

•In this process, some fats are fully hydrogenated and then

interesterified with other unhydrogenated fats to achieve the desired

properties, such as melting point or plasticity and avoid crystallisation

of particular fractions in the fats.

•Salatrium – a structured TG produced from the interesterification of long-

(mainly 18:0) and short- (2C, 3C, 4C) chain sat’d fatty acids. Caloric content

is ~ 5kcal/g.

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Pro Nutr Soc 64:205-212, 2005

Digestion of dietary PL relies on pancreatic enzyme Phospholipase A2

(targets sn2- fatty acid), generating lysophospholipid.

e.g. Phosphatidylcholine becomes lysophosphatidylcholine, which in

turn will be act on by lysophospholipase giving rise to

glycerylphosphorylcholine.

Intestinal Resynthesis

In the endoplasmic reticulum of enterocytes, resynthesis of

TG and CE occurs for assembly into Chylomicron. TG

resynthesis occurs mainly via the sn2-MAG pathway

(accounting for ~80%). The remaining 20% via the glycerol

phosphate (phosphatidic acid) pathway.

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Prog Lipid Res 43:105-133, 2004

(thiokinase)

Glycerol 3-phosphate

sn2-MAG