1. By: Andie Carman and Brianna Taylor
Lipids 13.1 – 13.3
By: Andie Carman and Brianna Taylor

2. 13.1 What Are Lipids
Lipids
A family of substances that are insoluble in water but soluble in nonpolar solvents of low polarity
Example: Diethyl Ether
Defined in terms of a property

3. Classification by Function
Three major roles in human biochemistry:
Store energy within fat cells
Parts of membranes that separate compartments of aqueous solutions from each other
Serve as chemical messengers

4. Storage Energy storage of lipids most important in animals
Animals and humans
More “economical” to use fats instead of carbohydrates
Carbohydrates = quick energy
Lipids = longer lasting energy
Produce twice as much energy
9 kcal/g vs. 4 kcal/g

5. Membrane Components Lack of water solubility is important
Body chemistry is so greatly based on water
Lipids are needed in compounds so membranes can separate compartments that contain aqueous solutions
Why are they insoluble?
Polar groups are smaller than alkane-like portions
Nonpolar portions provide hydrophobic property

6. Messengers Serve as chemical messengers Primary messengers
Deliver signals from one part of the body to another part
Example: hormonal steroids
Secondary messengers
Mediate the hormonal response
Example: Prostaglandins and thromboxanes

7. Classification by structure
Classified into four groups
Simple lipids
Fats and waxes
Complex lipids
Steroids
Prostaglandins, thromboxanes, leukotrienes

8. 13.2 What are the structures of triglycerides?
Triesters of glycerol and long-chain carboxylic acids (fatty acids)
Ex: animal fats and plant oils
Can have a combination of fatty acids
What fatty acids have in common:
Practically all unbranched carboxylic acids
About carbons
Contain even number of carbon atoms
Besides –COOH group, they have no functional groups
Most fatty acids that have double bonds, cis isomers predominate

9. Triglycerides
Even numbers of carbon because body builds them entirely from acetate and carbons are put in two at a time
Mono- and diglycerides are not infrequent
Complex mixtures
Some contain three identical fatty acids
Most contain two or three different fatty acids
Insoluble in water because ester groups are buried in nonpolar environment

10. 13.3 Properties of Triglycerides
Fats – come from animals, solid at room temp. Fish and plants, liquid at room temp.
Oils- liquid fats
Structural differences
Depends on degree of unsaturation
Physical properties
Same properties as fatty acids
Solid animal fats – contain saturated fatty acids
Vegetable oils – contain unsaturated fatty acids
Except coconut oil
Essential fatty acids
Body cannot synthesize them
Must be obtained through daily diet

11. Coconut oil Polyunsaturated Pure fats and oils
Small amount unsaturated acids
Liquid because rich in low-molecular-weight fatty acids
Polyunsaturated
More than one double bond per fatty acid chain
Pure fats and oils
Colorless, odorless, tasteless
Ex: butter
Taster and color come from small amounts of other substances dissolved in the fat or oil

12. Hydrogenation Can reduce carbon-carbon double bonds to single bonds
With hydrogen and a catalyst
Used to produce
Crisco
Partial hydrogenation
Used to make margarine
Less hydrogen is used
More unsaturation
Source of trans fatty acids

13. Saponification
Glycerides are esters, therefore are subject to hydrolysis
Carried out with acids or bases
Saponification
Base-promoted hydrolysis of fats and oils
Produce glycerol and a mixture of fatty acid salts called soaps