LIPIDS IIILIPIDS III

STEROLS

Cholesterol

Male & female sex hormones

Bile acids

Vitamin D

Adrenal corticosteroids HO

H3C

H3C

H3C CH3

CH3

123 4 5

6 789

10

1112

1314 15

1617

18

21 22

19

20

Sterols

Compounds with multi-ring structure Insoluble in water Present both in plant and animal foods Major sterol is cholesterol

However, cholesterol is found only in animal products (manufactured in liver)

High content in organ meats and egg yolk

Structure of steroid hormones:

Common Sterol Compounds

Vitamin D3 (cholecalciferol)

OH

CH3

CH3

C

O

O R2R1

HOR1 = OH or H

R2 = H or NH CH2 COOH or NH CH2 CH2 SO3

H

Bile Acids

Bile acids (bile salts) are polar derivatives of cholesterol, formed in liver and secreted into the gall bladder. They pass via the bile duct into the intestine, where they aid digestion of fats & fat-soluble vitamins. Bile acids are amphipathic, with detergent properties. Bile acids emulsify fat globules into smaller micelles, increasing the surface area accessible to lipid-hydrolyzing enzymes. They also help to solubilize lipid breakdown products (e.g., mono- & diacylglycerols from triacylglycerol hydrolysis).

Molecular complexes found in blood plasma Contain:

Neutral lipid core of cholesterol esters and/or TAGs

Surrounded by a layer of: Phospholopid Cholesterol Protein

Classes: Chylomicrons, VLDL, LDL, HDL

Lipoproteins

Model Structure of a Plasma Lipoprotein

Major Classes of Lipoproteins

Chylomicrons: Very large and very low density Transport intestineadipose

VLDL: Made in liver Transport lipids to tissues

LDL: carry cholesterol to tissues HDL:

Made in liver Scavenge excess cholesterol esters “Good cholesterol”

0%

20%

40%

60%

80%

100%

Chylo-microns

VLDL LDL HDL

Lipoprotein Type

Com

posi

tion

C

P

T

C

P

T

T

P

C

C P

T

The major classes of lipoproteins and their relative content of triacylglycerol (T),cholesterol (C) and protein (P).

Relative Composition of Lipoproteins

Lipid peroxidation a non-enzymatic reaction catalyzed

by oxygen may occur in tissues or in foods

(spoilage) the hydroperoxide formed is very

reactive and leads to the formation of free radicals which oxidize protein and/or DNA (causes aging and cancer)

principle is also used in drying oils (linseed, tung, walnut) to form hard films

13

Learning Check PL1

Identify each lipid as: (1) phospholipid (2) steroid

(3) triglyceride (4) sphingolipid A. CholesterolB. Glycerol, 2 fatty acids, phosphate, and cholineC. Glyceryl tristearateD. Sphingosine, fatty acid, phosphate, and cholineE. EstradiolF. Bile saltsG. Most of plasma membranes

14

Solution PL1

A. 2 steroidB. phospholipidC. 3 triglycerideD. 4 sphingolipidE. 2 steroidF. 2 steroidG. 1 phospholipid

ABDULLATIF TAHA ABDULLAABDULLATIF TAHA ABDULLADep. Of BIOCHEMISTRYDep. Of BIOCHEMISTRY