Lipids

Lipids
By: Henry Wormser, Ph.D.

Introduction
* Definition: water insoluble compounds
+ Most lipids are fatty acids or ester of fatty acid
+ They are soluble in non-polar solvents such as petroleum ether, benzene, chloroform
* Functions
+ Energy storage
+ Structure of cell membranes
+ Thermal blanket and cushion
+ Precursors of hormones (steroids and prostaglandins)
* Types:
+ Fatty acids
+ Neutral lipids
+ Phospholipids and other lipids
Fatty acids
* Carboxylic acid derivatives of long chain hydrocarbons
o Nomenclature (somewhat confusing)
+ Stearate – stearic acid – C18:0 – n-octadecanoic acid
o General structure:
* Common fatty acids
n = 4 butyric acid (butanoic acid)
n = 6 caproic acid (hexanoic acid)
n = 8 caprylic acid (octanoic acid)
n = 10 capric acid (decanoic acid)
* common FA’s:

n = 12: lauric acid (n-dodecanoic acid; C12:0)
n = 14: myristic acid (n-tetradecanoic acid; C14:0)
n = 16: palmitic acid (n-hexadecanoic acid; C16:0)
n = 18; stearic acid (n-octadecanoic acid; C18:0)
n = 20; arachidic (eicosanoic acid; C20:0)
n= 22; behenic acid
n = 24; lignoceric acid
n = 26; cerotic acid

Less common fatty acids
* iso – isobutyric acid
* anteiso
* odd carbon fatty acid – propionic acid
* hydroxy fatty acids – ricinoleic acid, dihydroxystearic acid, cerebronic acid
* cyclic fatty acids – hydnocarpic, chaulmoogric acid

PHYTANIC ACID
A plant derived fatty acid with 16 carbons and branches at C 3, C7, C11 and C15. Present in dairy products and ruminant fats.
A peroxisome responsible for the metabolism of phytanic acid is defective in some individuals. This leads to a disease called Refsum’s disease
Refsum’s disease is characterized by peripheral polyneuropathy, cerebellar ataxia and retinitis pigmentosa
Less common fatty acids
These are alkyne fatty acids
Fatty acids
* Fatty acids can be classified either as:
o saturated or unsaturated
o according to chain length:
Unsaturated fatty acids
* Monoenoic acid (monounsaturated)
Double bond is always cis in natural fatty acids.
This lowers the melting point due to “kink” in the chain
* Dienoic acid: linoleic acid
* Various conventions are in use for indicating the number and position of the double bond(s)
* Polyenoic acid (polyunsaturated)
* Monoenoic acids (one double bond):
* Trienoic acids (3 double bonds)
* Tetraenoic acids (4 double bonds)
* Pentaenoic acid (5 double bonds)
* Hexaenoic acid (6 double bonds)
Both FAs are found in cold water fish oils
Typical fish oil supplements
Properties of fats and oils
* fats are solids or semi solids
* oils are liquids
* melting points and boiling points are not usually sharp (most fats/oils are mixtures)
* when shaken with water, oils tend to emulsify
* pure fats and oils are colorless and odorless (color and odor is always a result of contaminants) – i.e. butter (bacteria give flavor, carotene gives color)
Examples of oils
* Olive oil – from Oleo europa (olive tree)
* Corn oil – from Zea mays
* Peanut oil – from Arachis hypogaea
* Cottonseed oil – from Gossypium
* Sesame oil – from Sesamum indicum
* Linseed oil – from Linum usitatissimum
* Sunflower seed oil – from Helianthus annuus
* Rapeseed oil – from Brassica rapa
* Coconut oil – from Cocos nucifera.....


Websites on lipids

* http://www.cyberlipid.org/ web site deals mainly with an overview on all lipids
* http://www.lipidsonline.org – this website focuses mainly on disease processes (atherosclerosis) and treatment
* http://www.lipidlibrary.co.uk/ -There are two main divisions in this website, one dealing with the chemistry and biochemistry of lipids and the other with the analysis of lipids


Lipids.ppt