Lipid Structure and Function

Pages 27-36 in textbook

Common Physical Properties of Lipids Soluble in non-polar organic solvents Contain C, H, O

Sometimes N & P Includes fats and oils – mostly

triglycerides 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 CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CO

OH

HCCH

HCCHCHCH2OH

O

HOHO

OHHO

H+

ATP

Energy-Containing Nutrients (C and H)

CO2

ElectronTransportChain

H2OO2

Lipids or Glucose for Energy?

H3C CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CO

OH

HCCH

HCCHCHCH2OH

O

HOHO

OHHO

More reduced state (more H bound to C) More potential for oxidation

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

Protects nerves, help conduct electro-chemical impulses (myelin sheath)

Supply essential fatty acids (EFA) 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

Immune system, nervous systems, and GI secretions Regulatory functions: lower BP, blood clotting, uterine

contractions Help transport fat soluble vitamins Palatability and aroma

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

Fatty Acid Structure

H - C - ( C )n - C - OH

- H

- H

- H

- H=

OCarboxyl group

Carbon group(s)

Methyl 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-C- No 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,

poly-unsaturated 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

Fish oil is rich in odd-numbered FAs Double bonds

Number Location from methyl or carboxyl end Degree of “saturation”

H3C CH2

CH

CH

CH2

CH

CH

CH2

CH

CH

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CO

OH

Fatty-acid Nomenclature Named according to

chain length C18

H3C CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CO

OH

Fatty-acid Nomenclature Named according to the number of

double bonds C18:0

H3C CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CO

OH

Common name:Stearic acid

H3C CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH

CH

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CO

OH

Fatty-acid Nomenclature Named according to the number of

double bonds C18:1

Common name:Oleic acid

H3C CH2

CH2

CH2

CH2

CH

CH

CH2

CH

CH

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CO

OH

Named according to the number of

double bonds C18:2

Fatty-acid Nomenclature

Common name:Linoleic acid

H3C CH2

CH

CH

CH2

CH

CH

CH2

CH

CH

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CO

OH

Named according to the number of

double bonds C18:3

Fatty-acid Nomenclature

Common name:Linolenic acid

Named according to the location of the first double bond from the non-carboxyl end (count from the methyl end) Omega system (e.g., omega 3, 3) n–system (e.g., n–3)

Fatty-acid Nomenclature

H3C CH2

CH

CH

CH2

CH

CH

CH2

CH

CH

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CO

OH

Fatty-acid NomenclatureH3C C

H2

CH2

CH2

CH2

CH2

CH2

CH2

CH

CH

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CO

OH

H3C CH2

CH2

CH2

CH2

CH

CH

CH2

CH

CH

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CO

OH

H3C CH2

CH

CH

CH2

CH

CH

CH2

CH

CH

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CO

OH

Omega 9 or n–9 fatty acid

Omega 6 or n–6 fatty acid

Omega 3 or n–3 fatty acid

Fatty Acid Synthesis Issues

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

Ω-3 Ω-6 Ω-9

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)

CH C

H2

CH2

CH2

CH2

CH2

CH2

CH2

CH3C CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH O

OH

Fatty-acid Nomenclature

CH

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CO

OH

H 3CC

H 2

CH 2

CH 2

CH 2

CH 2

CH 2

CH 2

CH

Isomers Geometrical isomers

due to double bond Cis

occurs naturally bend in acyl chain

Trans Not as common Found in

hydrogenated oils Results from

bacterial synthesis In fats in

ruminants!! Straight acyl chains

Chain branching Straight

Synthesized by mammals and plants

Branched Synthesized by

bacteria

Cis Fatty Acids

Melting Points Affected by chain length

Longer chain = higher melting temp

Fatty acid: C12:0 C14:0 C16:0 C18:0 C20:0Melting point: 44°C 58°C 63°C 72°C 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: C18:0 C18:1 C18:2 C18:3Melting point: 72°C 16°C –5°C –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 butterfatCaproic 6 0 6:0 butterfatCaprylic 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)

Omega-6-FA Linolenic acid (18:3)

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 One fatty acid is replaced by a sugar (galactose)

Triacyl glycerols (triglycerides) 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

Glycerol

Fatty Acid

Fatty Acid

Fatty Acid

Triglyceride Structure Fatty acid composition of triglyceride varies

according to function Membrane lipids must be fluid at all

temperatures Contain more unsaturated fatty acids

Lipids in tissues subjected to cooling (e.g., hibernators or tissues in extremities)

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 Di- and TriglyceridesFatty acid Carbon:Double bonds Double bonds

Myristic 14:0Palmitic 16:0Palmitoleic 16:1 Cis-9

Stearic 18:0Oleic 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

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 Several metabolic functions

Steroids 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

                                                                              

                        

Stigmasterol(a phytosterol)

Cholesterol(a sterol)

Vitamin D3(cholecalcifero

l)

Testosterone(a steroid hormone)