1. Lipids Function of Lipids
Energy storage molecules in animals [release 9 kcal/g versus 4 kcal/g by carbohydrates]
Form membranes (cellular or sub-cellular) that separate compartments in cells [lipids are insoluble in water so help generate membranes]
Serve as chemical messengers [steroid hormones are primary messengers, while prostaglandins and thromboxanes are secondary messengers mediating hormonal response]
MEDC 527 Fall 2008

2. Simple and Complex Lipids Glycerophospholipids
Classification of Lipids by Structure
Lipids can be classified into four groups based on their structure
1) Simple lipids, e.g., fats; 2) Complex lipids
3) Steroids; 4) Prostaglandins, thromboxanes, and leukotrienes
Simple and Complex Lipids
Simple
Complex
Phospholipids
Glycolipids
Glycerophospholipids
Sphingolipids
Fatty acid
Glycerol
Alcohol
PO4
choline
Sphingosine
Glup / Galp
MEDC 527 Fall 2008

3. Lipids Triglycerides Animal fats and vegetable oils are triglycerides
Triesters of glycerol and long chain carboxylic acids called fatty acids
Glycerol component cannot vary, but the fatty acid component may vary
Fatty acids are unbranched carboxylic acids having 10 to 20 carbons in even number
Some fatty acids have double bond(s). Typically these double bond(s) are cis n +
A triglyceride p
Glycerol m
palmitate (16:0)
oleate (18:1)
stearate (18:0)
MEDC 527 Fall 2008

4. Properties of Triglycerides
Generally fats from animals are solids at room temperature. Most fats from plants and fish are liquids. Liquid fats are referred to as oils.
Presence or absence of unsaturation makes a triglyceride solid or liquid
Saturated and trans fatty acids stack well Unsaturated cis fatty acids do not ….
(greater hydrophobic interactions; (lesser hydrophobic interactions;
greater order in arrangement; lesser order in arrangement;
carries over to triglyceride structure) carries over to triglyceride structure)
MEDC 527 Fall 2008

5. Properties of Triglycerides
Saturated Fatty Acids Tm (OC)
12:0 CH3(CH2)10COOH lauric acid 44
14:0 CH3(CH2)12COOH myristic acid 58
16:0 CH3(CH2)14COOH palmitic acid 63
18:0 CH3(CH2)16COOH stearic acid 70
20:0 CH3(CH2)18COOH arachidic acid 77
Unsaturated cis Fatty Acids
16:1 CH3(CH2)5 CH=CH(CH2)7COOH palmitoleic acid 1
18:1 CH3(CH2)7 CH=CH(CH2)7COOH oleic acid 16
18:2 CH3(CH2)4 (CH=CHCH2)2(CH2)6COOH linoleic acid -5
18:3 CH3CH2(CH=CHCH2)3(CH2)6COOH linolenic acid -11
20:4 CH3(CH2)4 (CH=CHCH2)4(CH2)2COOH arachidonic acid -49
MEDC 527 Fall 2008

6. Mixture of fatty acid sodium salt
Properties of Triglycerides
Pure fats and oils are colorless, odorless and tasteless.
Fats are not soluble in water. They are hydrophobic molecules and soluble in organic solvents
The presence of double bonds, especially in plant fats, makes them susceptible to oxidation. Heavily oxidized fats are not edible. These generate rancidity.
The ester group in fats is susceptible to hydrolysis releasing acidic groups, e.g., butyric acid, which have bad taste and odor.
NaOH _ _ _ + + + +
Mixture of fatty acid sodium salt
(Soap)
Saponification
MEDC 527 Fall 2008

7. Complex Lipids
Complex lipids constitute the main component of membranes.
Two main types of complex lipids – phospholipids and glycolipids. Phospholipids contain a phosphate group, while glycolipids contain a carbohydrate group
Phospholipids can be made from glycerol or from sphingosine +
choline _
Phosphatidylcholine (lecithin)
(A glycerophospholipid)
A sphingomyelin (A sphingolipid)
sphingosine + + _
choline
MEDC 527 Fall 2008

8. The Fluid Mosaic Model of Cell Membranes
Complex lipids containing unsaturated fatty acids constitute cell membranes.
Membranes are made up of lipid bi-layers.
The Fluid Mosaic Model of Cell Membranes
MEDC 527 Fall 2008

9. Cyclopentanoperhydrophenanthrene
Steroids
Steroids constitute the third major class of lipids
Steroids are cyclopentanoperhydrophenanthrenes.
Cholesterol is the commonest steroid. It is present cell membranes. It is also present in lipoprotein particles, e.g., LDL, HDL, and others A B C D
Cyclopentanoperhydrophenanthrene
(Steroid skeleton)
Cholesterol
MEDC 527 Fall 2008

10. A Model of a Lipoprotein Particle
Lipoprotein Particles
Lipoprotein particles transport cholesterol in blood
Contain a core of hydrophobic lipid molecules surrounded by a shell of hydrophilic molecules such as proteins and phospholipids
At least four kinds of particles: HDL, LDL, VLDL and Chylomicrons
Apolipoprotein
Cholesterol
Phospholipids
Cholesterol ester
A Model of a Lipoprotein Particle
MEDC 527 Fall 2008

11. Prostaglandins, Thromboxanes and Leukotrienes
Prostaglandins are derived from arachidonic acid
They have a wide variety of effects of the body; they can lower or raise blood pressure, cause inflammation, induce blood clotting and induce labor
Aspirin and other NSAIDs inhibit the enzyme (cyclooxygenase COX) involved in the synthesis of prostaglandins
Arachidonic Acid
PGE2
PGF2a
Thromboxane A2
Leukotriene B4
MEDC 527 Fall 2008