Lipid Structure and
Function
Pages 27-36 in textbook
Common Physical Properties
of Lipids


Soluble in non-polar organic solvents
Contain C, H, O


Includes fats and oils – mostly triglycerides



Sometimes N & P
Fat: solid at room temperature
Oil: liquid at room temperature
More highly reduced than CHO

2.25x more energy
Lipids or Glucose for Energy?
H3C
C
H2
HC
HO
H2
C
HO
CH
HO
CH
C
H2
H2
C
C
H2
H2
C
OH
C
H2
H2
C
C
H2
H2
C
C
H2
H2
C
C
H2
H2
C
O
C
OH
Energy-Containing Nutrients (C and H)
O
CH
HC
C
H2
H2
C
ATP
Electron
Transport
Chain
H+
CO2
CH2OH
H2O
O2
Lipids or Glucose for Energy?
H3C
C
H2
H2
C
HC
HO
C
H2
H2
C
O
C
H2
H2
C
C
H2
H2
C
C
H2
H2
C
C
H2
H2
C
C
H2
H2
C
C
H2
H2
C
O
C
OH
More reduced state (more H bound to C)
 More potential for oxidation
CH
HC
HO
CH
HO
CH
OH
CH2OH
Less reduced state (more O bound to C)
 Less potential for oxidation
Energy from Lipids


Compared to carbohydrates, fatty acids
contain more hydrogen molecules per unit of
carbon, thus, they are in a more reduced
form
Carbohydrates are partially oxidized so they
contain less potential energy (H+ and e-) per
unit of carbon
Functions and Properties



Concentrated source of energy (9 kcal/gm)
Energy reserve: any excess energy from
carbohydrates, proteins and lipids are stored
as triglycerides in adipose tissues
Provide insulation to the body from cold


Maintain body temperature
Mechanical insulation

Protects vital organs
Functions and Properties

Electrical insulation


Supply essential fatty acids (EFA)


Protects nerves, help conduct electro-chemical
impulses (myelin sheath)
Linoleic acid and linolenic acid
Formation of cell membranes

Phospholipids, a type of fat necessary for the
synthesis of every cell membrane (also
glycoproteins and glycolipids)
Functions and Properties

Synthesis of prostaglandins from fatty acids

Hormone-like compounds that modulates many
body processes




Help transport fat soluble vitamins
Palatability and aroma


Immune system, nervous systems, and GI secretions
Regulatory functions: lower BP, blood clotting, uterine
contractions
Flavor and taste for some species!
The satiety value – help control appetite

Fullness; fats are digested slower

Regulated through gastric inhibitory protein (GIP) and
cholecystokinin (CCK)
Physical Traits of Fatty Acids

Form membranes, micelles, liposomes

Orient at water:oil interface
Contain hydrophobic and hydrophilic groups
Lipid bilayer for membranes

Micelles formed during digestion


Physical Traits of Fatty Acids

Fatty acids form “soaps” with cations


Na & K soaps – water soluble
Ca & Mg soaps – not water soluble


Poorly digested
Major issue in feeding fats to ruminants
Physical Traits of Fatty Acids

Unsaturated fatty acids oxidize
spontaneously in presence of oxygen


Auto-oxidation, peroxidation, rancidity
Free radicals formed


Reduce nutritional value of fats
Antioxidants prevent oxidation

Vitamins C and E, selenium
-H
-H
-H
=O
-H
Fatty Acid Structure
H - C - ( C )n - C - OH
Methyl
group
Carbon
group(s)
Carboxyl
group
Fatty Acids

With a few exceptions, natural fatty acids:




Contain an even number of carbon atoms
Arranged in an unbranched line
Have a carboxyl group (-COOH) at one end
Have a methyl group (CH3) at the other end
Fatty Acid Chain Length





Short chain: 2 to 6 C (volatile fatty acids)
Medium chain: 8 – 12 C
Long chain: 14 – 24 C
As chain length increases, melting point
increases
Fatty acids synthesized by plants and animals
have an even number of carbons


Mostly long chain
16C to 18C fatty acids are most prevalent
Fatty Acid Saturation


Saturated - no double bonds
Unsaturated – contain double bonds




Monounsaturated – one double bond
Polyunsaturated - >1 double bond
The double bond is a point of
unsaturation
As number of double bonds increases,
melting point decreases
Saturated Fats




All the chemical bonds between the carbon
are single bonds
C-C-CNo double bonds
No space for more H atoms; fully “saturated”
Solid at room temperature


Butter, shortening, lard, coconut oil, palm oil, and
fully hydrogenated vegetable oils
Poultry skin, whole milk
Mono-Unsaturated Fatty Acids

Only one double bond


Therefore, two H atoms can be added
Liquid at room temperature


Olive oil, canola oil, peanut oil
Other sources: avocado, almonds,
cashews, pecans and sesame seeds (tahini
paste)
Poly-Unsaturated Fatty Acids


Two or more double bonds
Include omega-3 and omega-6 fatty acids
(essential fatty acids)



Linolenic acid: omega 3 fatty acid
Linoleic acid: omega 6 fatty acid
Richest sources of poly-unsaturated fatty
acids include:

Vegetable oils

Corn, sunflower, safflower, cotton seed oils
Saturation

Unsaturated fatty acids


Converted to saturated fatty acids by rumen
microbes
More susceptible to rancidity


Oxidation of double bonds produces peroxides and free
radicals, which can cause damage to other compounds
Antioxidants


Vitamins E, C
Carotenoids


Such as beta-carotene, lycopene
Selenium
Hydrogenation of Fatty Acids

To protect fats from becoming rancid, polyunsaturated fatty acids may be hydrogenated



Increases saturation and stability - more resistant
to oxidation
Unsaturated fats entering rumen are naturally
hydrogenated (“bio”-hydrogenated)
Transforms the H-H configuration from cis to trans
configuration


Trans configuration alters biological availability
Trans configuration alters biological effects
Review of Fatty Acid
Nomenclature

Chain length

Most fatty acids have an equal number of carbons


Double bonds



H3C
Fish oil is rich in odd-numbered FAs
H
C
C
H2
Number
Location from methyl or carboxyl end
Degree of “saturation”
C
H
H2
C
C
H
H
C
H
C
C
H2
C
H
H2
C
C
H2
H2
C
C
H2
H2
C
C
H2
H2
C
O
C
OH
Fatty-acid Nomenclature

Named according to
chain length

H3C
C
H2
C18
H2
C
C
H2
H2
C
C
H2
H2
C
C
H2
H2
C
C
H2
H2
C
C
H2
H2
C
C
H2
H2
C
C
H2
H2
C
O
C
OH
Fatty-acid Nomenclature

Named according to the number of
double bonds

H3C
C
H2
C18:0
H2
C
C
H2
H2
C
C
H2
H2
C
C
H2
H2
C
C
H2
H2
C
C
H2
H2
C
Common name:
Stearic acid
C
H2
H2
C
C
H2
H2
C
O
C
OH
Fatty-acid Nomenclature

Named according to the number of
double bonds

H3C
C
H2
C18:1
H2
C
C
H2
H2
C
C
H2
H2
C
H
C
C
H2
C
H
H2
C
C
H2
Common name:
Oleic acid
H2
C
C
H2
H2
C
C
H2
H2
C
O
C
OH
Fatty-acid Nomenclature

Named according to the number of
double bonds

H3C
C
H2
C18:2
H2
C
C
H2
H2
C
C
H
H
C
H
C
C
H2
C
H
H2
C
C
H2
H2
C
Common name:
Linoleic acid
C
H2
H2
C
C
H2
H2
C
O
C
OH
Fatty-acid Nomenclature

Named according to the number of
double bonds

H3C
C18:3
H
C
C
H2
C
H
H2
C
C
H
H
C
H
C
C
H2
C
H
H2
C
C
H2
H2
C
Common name:
Linolenic acid
C
H2
H2
C
C
H2
H2
C
O
C
OH
Fatty-acid Nomenclature

Named according to the
location of the first double bond from
the non-carboxyl end (count from the
methyl end)


H3C
Omega system (e.g., omega 3, 3)
n–system (e.g., n–3)
H
C
C
H2
C
H
H2
C
C
H
H
C
H
C
C
H2
C
H
H2
C
C
H2
H2
C
C
H2
H2
C
C
H2
H2
C
O
C
OH
Fatty-acid Nomenclature
H3C
C
H2
H2
C
C
H2
H2
C
C
H2
H2
C
H
C
H2
C
C
H
C
H2
C
H2
H2
C
C
H2
H2
C
C
H2
H2
C
O
C
OH
Omega 9 or n–9 fatty acid
H3C
C
H2
H2
C
C
H2
H2
C
C
H
H
C
H
C
C
H2
C
H
H2
C
C
H2
H2
C
C
H2
H2
C
C
H2
H2
C
O
C
OH
Omega 6 or n–6 fatty acid
H3C
H
C
C
H2
C
H
H2
C
C
H
H
C
H
C
C
H2
C
H
H2
C
C
H2
H2
C
C
H2
Omega 3 or n–3 fatty acid
H2
C
C
H2
H2
C
O
C
OH
Fatty Acid Synthesis Issues
Ω-3
Ω-6
Ω-9
C-C-C=C-C-C=C-C-C=C-C-C-C-C-C-C-C-COOH

Animals can synthesize a fatty acid with a
double bond in the omega 9 position but not
at either 3 or 6 positions


Omega-3 and omega-6 fatty acids must be
derived from diet
Cold water fish accumulate high levels of
omega 3 fatty acids from their diet
Omega System and
Essential Fatty Acids


Linoleic acid is an omega-6 fatty acid
Linolenic and arachidonic acids are
omega-3 fatty acids


Linoleic and linolenic acids are essential
fatty acids
Arachidonic acid can be synthesized from
linoleic acid, so not essential

Exception is cats (of course)
Fatty-acid Nomenclature

Named according to location of H’s

Cis or trans fatty acids
Cis-9-octadecenoic acid
(Oleic acid)
Trans-9-octadecenoic acid
(Elaidic acid)
Fatty-acid Nomenclature
H3C
C
H2
H2
C
C
H2
H2
C
C
H2
H2
C
C
H2
H
C
H
C
C
H C
H2
C
H2
H2
C
H2
C
C
H2
C
H2
H2
C
H2
C
C
H2
C
H2
H2
C
H2
C
O
C
H2
C
O
C
H2
C
OH
OH
Isomers

Geometrical isomers due
to double bond

Cis





occurs naturally
bend in acyl chain

Straight

In fats in ruminants!!
Straight acyl chains
Synthesized by
mammals and plants
Branched

Not as common
Found in hydrogenated
oils
Results from bacterial
synthesis


Chain branching

Trans


Synthesized by bacteria
Cis Fatty Acids
Melting Points

Affected by chain length

Longer chain = higher melting temp
Fatty acid:
C12:0
Melting point: 44°C
C14:0
58°C
C16:0
63°C
C18:0
72°C
C20:0
77°C
Which fatty acids are liquid at room temperature?
Which fatty acids are solid at room temperature?
Chain Length

In most fats with a mixture of fatty acids, the
chain length of the majority of fatty acids will
determine the “hardness” of the fat



<10 carbons = liquid
Between 10 and 20 carbons = ???
>20 carbons = solid
Acetic Acid (2 C)
Vinegar
Liquid
Stearic Acid (18 C)
Beef Tallow
Solid
Arachidic Acid (20 C)
Butter
Solid
Melting Points

Affected by number of double bonds

More saturated = higher melting temp
Fatty acid:
Melting point:
C18:0
72°C
C18:1
16°C
C18:2
–5°C
C18:3
–11°C
Which fatty acid is liquid at room temperature?
Which fatty acids are solid at room temperature?
Acids
Carbons
Double bonds
Abbreviation
Source
Acetic
2
0
2:0
bacterial metabolism
Propionic
3
0
3:0
bacterial metabolism
Butyric
4
0
4:0
butterfat
Caproic
6
0
6:0
butterfat
Caprylic
8
0
8:0
coconut oil
Capric
10
0
10:0
coconut oil
Lauric
12
0
12:0
coconut oil
Myristic
14
0
14:0
palm kernel oil
Palmitic
16
0
16:0
palm oil
Palmitoleic
16
1
16:1
animal fats
Stearic
18
0
18:0
animal fats
Oleic
18
1
18:1
olive oil
Linoleic
18
2
18:2
grape seed oil
Linolenic
18
3
18:3
flaxseed (linseed) oil
Arachidonic
20
4
20:4
peanut oil, fish oil
Essential Fatty Acids

Must be in diet


Tissues can not synthesize
Linoleic acid (18:2)


Linolenic acid (18:3)


Omega-6-FA
Omega-3-FA
Arachidonic (20:4)


Not found in plants!
Can be synthesized from C18:2 (linoleic acid) in most
mammals (except in cat)

Essential nutrient in the diet of cats
Functions of Essential
Fatty Acids



A component of the phospholipids in
cell membranes
Precursor for prostaglandins:
arachidonic acid
Important metabolic regulator



Contraction of smooth muscle
Aggregation of platelets
Inflammation
Arachidonic Acid

Prostaglandins






Thrombocyclin
Prostacyclin
Leukotrenes
Neurotransmitters
Cychrome P450
Synthesized in liver

elongates linoleic acid (C18:2)
Essential Fatty Acids

Since dietary poly-unsaturated fatty
acids are hydrogenated to saturated
fatty acids in the rumen by the
microbes, how do ruminants meet their
essential fatty acid requirement?


By-pass (rumen protected) lipids
Microbial lipid synthesis

Microbes don’t utilize lipids for energy, but they
do synthesize them for their cell membranes
Essential Fatty Acids

Deficiency of essential fatty acid
intakes:




Growth retardation
Problems with reproduction
Skin lesions
Kidney and liver disorders
Simple Lipids

Neutral fats and oils


Monoacyl glycerols (monoglycerides)
Diacyl glycerols (diglycerides)
 Diglycerides found in plant leaves


Triacyl glycerols (triglycerides)


One fatty acid is replaced by a sugar (galactose)
Triglycerides found in seeds and
animal adipose tissue
Triacyl glycerols (triglycerides)

Lipid storage form


Where in the body? Adipocytes!!
Most lipids consumed are triglycerides
Triglycerides


Most common structure in dietary lipids
Composed of one glycerol molecule and three fatty
acids connected by an ester bond (bond between an
alcohol and and organic acid)

Fatty acids may be same or mixed
Fatty Acid
Fatty Acid
Glycerol
Fatty Acid
Triglyceride Structure

Fatty acid composition of triglyceride varies
according to function

Membrane lipids must be fluid at all temperatures


Lipids in tissues subjected to cooling
(e.g., hibernators or tissues in extremities)


Contain more unsaturated fatty acids
Contain more unsaturated FAs
Butterfat (milk fat) is fairly fluid
in spite of containing mostly saturated FAs

Why? Chain length!!
Most Common Fatty Acids in Diand Triglycerides
Fatty acid
Carbon:Double bonds
Double bonds
Myristic
14:0
Palmitic
16:0
Palmitoleic
16:1
Stearic
18:0
Oleic
18:1
Cis-9
Linoleic
18:2
Cis-9,12
Linolenic
18:3
Cis-9,12,15
Arachidonic
20:4
Cis-5,8,11,14
Eicosapentaenoic
20:5
Cis-5,8,11,14,17
Docosahexaenoic
22:6
Cis-4,7,10,13,16,19
CH3(CH2)nCOOH
Cis-9
Complex Lipids - Phospholipids

Two primary types:

Glycerophosphatides



Core structure is glycerol
Part of cell membranes, chylomicrons,
lipoproteins
Sphingophosphatides


Core structure is sphingosine
Part of sphingomyelin
Complex Lipids - Phospholipids


Glycerophosphatides resemble triglyceride in
structure except one of the fatty acids is
replaced by a compound containing a
phosphate group, or occasionally, nitrogen
Most prevalent is lecithin
Phospholipids

Significant use in feed industry as
emulsifiers


Lipids form emulsion in water
Phospholipid sources:



Liver, egg yolk,
Soybeans, wheat germ
Peanuts
Complex Lipids - Glycolipids


Carbohydrate component in structure
Cerebrosides & gangliosides

Medullary sheaths of nerves; white matter
of brain
Derived Lipids

Prostaglandins

Synthesized from arachidonic acid


Steroids


Several metabolic functions
Cholesterol, ergosterol, bile acids
Terpenes

Made by plants

Carotenoids, xanthophylls
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
Common Sterol Compounds
Cholesterol
(a sterol)
Testosterone
(a steroid hormone)
Vitamin D3
(cholecalciferol)
Stigmasterol
(a phytosterol)