1. Lipid Structure and Function

2. 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

3. Lipids or Glucose for Energy?
Energy-Containing Nutrients H+
ATP
Electron
Transport
Chain
CO2 O2
H2O

4. Lipids or Glucose for Energy?
More reduced state
 More potential for oxidation
Less reduced state
 Less potential for oxidation

5. 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

6. 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

7. 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)

8. 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)

9. 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

10. 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

11. 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

12. 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

13. Fatty Acid Structure - H - H = O H - C - ( C )n - C - OH - H - H
Carboxyl group
- H
- H
Carbon group(s)
Methyl group

14. 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

16. 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

17. 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

18. 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

19. 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)

20. 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

21. Saturation Unsaturated fatty acids Antioxidants
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

22. Fatty-acid Nomenclature
Named according to chain length
C18

23. Fatty-acid Nomenclature
Named according to the number of double bonds
C18:0
Common name:
Stearic acid

24. Fatty-acid Nomenclature
Named according to the number of double bonds
C18:1
Common name:
Oleic acid

25. Fatty-acid Nomenclature
Named according to the number of double bonds
C18:2
Common name:
Linoleic acid

26. Fatty-acid Nomenclature
Named according to the number of double bonds
C18:3
Common name:
Linolenic acid

27. Fatty-acid Nomenclature
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)

28. Fatty-acid Nomenclature
Omega 9 or n–9 fatty acid
Omega 6 or n–6 fatty acid
Omega 3 or n–3 fatty acid

29. 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

30. 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)

31. 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)

32. Fatty-acid NomenclatureH 3 C 2

33. Isomers Chain branching Straight Branched
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

34. Cis Fatty Acids

35. 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

36. 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”

37. 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?

38. 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

39. 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?

40. Acids
Carbons
Double bonds
Abbreviation
Source
Acetic 2
2:0
bacterial metabolism
Propionic 3
3:0
Butyric 4
4:0
butterfat
Caproic 6
6:0
Caprylic 8
8:0
coconut oil
Capric 10
10:0
Lauric 12
12:0
Myristic 14
14:0
palm kernel oil
Palmitic 16
16:0
palm oil
Palmitoleic 1
16:1
animal fats
Stearic 18
18:0
Oleic
18:1
olive oil
Linoleic
18:2
grape seed oil
Linolenic
18:3
flaxseed (linseed) oil
Arachidonic 20
20:4
peanut oil, fish oil

41. 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

42. 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

43. Arachidonic Acid Prostaglandins Synthesized in liver Thrombocyclin
Prostacyclin
Leukotrenes
Neurotransmitters
Cychrome P450
Synthesized in liver
elongates linoleic acid (C18:2)

44. 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

45. Essential Fatty Acids Deficiency of essential fatty acid intakes:
Growth retardation
Problems with reproduction
Skin lesions
Kidney and liver disorders

46. 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
Lipid storage form
Where in the body? Adipocytes!!
Most lipids consumed are triglycerides

47. 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!!

48. Most Common Fatty Acids in Di- and Triglycerides
Carbon:Double bonds
Double bonds
Myristic
14:0
Palmitic
16:0
Palmitoleic
16:1
Cis-9
Stearic
18:0
Oleic
18:1
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

49. 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

51. 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

52. Phospholipids Significant use in feed industry as emulsifiers
Lipids form emulsion in water
Phospholipid sources:
Liver, egg yolk,
Soybeans, wheat germ
Peanuts

53. Complex Lipids - Glycolipids
Carbohydrate component in structure
Cerebrosides & gangliosides
Medullary sheaths of nerves; white matter of brain

54. Derived Lipids Prostaglandins Steroids Terpenes
Synthesized from arachidonic acid
Several metabolic functions
Steroids
Cholesterol, ergosterol, bile acids
Terpenes
Made by plants
Carotenoids, xanthophylls

55. 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

56. Common Sterol Compounds
Vitamin D3 (cholecalciferol)
Cholesterol (a sterol)
                                                                                                      
Stigmasterol (a phytosterol)
Testosterone (a steroid hormone)