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Lipid Structure and Function
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?
H3CCH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
C
O
OH
HC
CH
HC
CH
CH
CH2OH
O
HO
HO
OH
HO H+
ATP
Energy-Containing Nutrients (C and H)
CO2
Electron Transport Chain
H2O
O2
Lipids or Glucose for Energy?
H3CCH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
C
O
OH
HC
CH
HC
CH
CH
CH2OH
O
HO
HO
OH
HO
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
= O
Carboxyl 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
Suppresses de novo milkfat synthesis in mammary gland
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”
H3CCH2
CH
CH
CH2
CH
CH
CH2
CH
CH
CH2
CH2
CH2
CH2
CH2
CH2
CH2
C
O
OH
Fatty-acid Nomenclature
Named according to chain length
C18
H3CCH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
C
O
OH
Fatty-acid Nomenclature
Named according to the number of double bonds
C18:0
H3CCH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
C
O
OH
Common name:
Stearic acid
H3CCH2
CH2
CH2
CH2
CH2
CH2
CH2
CH
CH
CH2
CH2
CH2
CH2
CH2
CH2
CH2
C
O
OH
Fatty-acid Nomenclature
Named according to the number of double bonds
C18:1
Common name:
Oleic acid
H3CCH2
CH2
CH2
CH2
CH
CH
CH2
CH
CH
CH2
CH2
CH2
CH2
CH2
CH2
CH2
C
O
OH
Named according to the number of double bonds
C18:2
Fatty-acid Nomenclature
Common name:
Linoleic acid
H3CCH2
CH
CH
CH2
CH
CH
CH2
CH
CH
CH2
CH2
CH2
CH2
CH2
CH2
CH2
C
O
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
H3CCH2
CH
CH
CH2
CH
CH
CH2
CH
CH
CH2
CH2
CH2
CH2
CH2
CH2
CH2
C
O
OH
Fatty-acid Nomenclature
H3CCH2
CH2
CH2
CH2
CH2
CH2
CH2
CH
CH
CH2
CH2
CH2
CH2
CH2
CH2
CH2
C
O
OH
H3CCH2
CH2
CH2
CH2
CH
CH
CH2
CH
CH
CH2
CH2
CH2
CH2
CH2
CH2
CH2
C
O
OH
H3CCH2
CH
CH
CH2
CH
CH
CH2
CH
CH
CH2
CH2
CH2
CH2
CH2
CH2
CH2
C
O
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 linoleic 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
CH3CCH2
CH2
CH2
CH2
CH2
CH2
CH2
CH O
OH
Fatty-acid Nomenclature
CH
CH2
CH2
CH2
CH2
CH2
CH2
CH2
C
O
OH
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 C20:0
Melting 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 C18:3
Melting 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 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) 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 Triglycerides
Fatty acid Carbon:Double bonds Double bonds
Myristic 14:0
Palmitic 16:0
Palmitoleic 16:1 Cis-9
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
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 (cholecalciferol)
Testosterone (a steroid hormone)
