1. Lipids General Characteristics Classification Biological function
Lipids and detergents (HW)

2. Characteristics (use in conjunction with Interactive Concepts in Biology)
Composed of a hydrocarbon chain (R or alkyl group), hydrogen groups and carboxyl group at the end of the chain
As the size of the alkyl group increases, the relative contribution of the carboxyl group to the physical properties of the molecule decreases
Insoluble in water, soluble in organic solvents, fat-soluble

3. What are lipids?
Are fat molecules or formed by dehydration or condensation reactions of fatty acids (an even # of carbons, typically carbons in the chain) and glycerol
Are involved in:
energy storage (triglycerols in fat cells) and utilization (some fatty acids are used as building blocks, most are used for energy production
structural elements of membranes,
hormones (steroids, sex hormones),
some aid in digestion and nutrient transport, may be part of proteins and carbohydrates1
1 Campbell, N. et al Biology Fifth Edition. Benjamin Cummings Publishing Company. United States

4. Classification of Lipids
Lipids are classified: according to solubility
Fats and oils (triglycerides), waxes, phospholipids, sterols
Formation of triglycerides:
Glycerol Fatty Acids TRIGLYCERIDE
Ester Linkage
Fatty acid chain could be saturated or unsaturated

5. Unsaturated fatty acids
Saturated with H
Contain single carbon- carbon covalent bonds
Examples:
16:0 Palmitic acid CH3(CH2)14COOH
18:0 Stearic acid CH3(CH2)16COOH
Unsaturated fatty acids
Contain 1 or more C-C double bonds (mono-poly)
Example:
18:1 Oleic acid CH3(CH2) CH=CH (CH2) 7COOH

6. …or according to behavior in basic environments
Lipids are often classified as saponifiable and nosaponifiable.
Saponifiable: are hydrolyzed by bases (strong bases NaOH, KOH) to give salts and alcohol. Examples include tryglycerols, glycolipids, phospholipids, and some waxes
Nonsaponifiable: not hydrolyzed by base. Examples: steroids, prostaglandins, some waxes.
Saponification = base catalyzed hydrolysis

7. Lipids and Detergents Soaps are salts of fatty acids (Na or K salts)
The hydrocarbon portion (the tail) of the fatty acid salt is water-insoluble but the ionic is water soluble, even more than alcohol!!
“Grease (and dirt) have the hydrocarbon character and so it dissolves in the hydrocarbon chains of the soap molecules

8. Hydrophilic and Hydrophobic and lipophilic (tail)
Water Hydrocarbons
Hydrophilic and Hydrophobic and lipophilic (tail)
Lipophobic portion of soap portion of the soap
Soluble in hydrocarbon part of
fatty acid

9. Then how does it help “dissolve” lipids?
As a consequence oil (and dirt) bits are collected in the center of a micelle.
Micelles stay in basic solutions as a colloid and do not come together to precipitate because of the ion repulsion

10. Biological Function of Lipids
Triglycerides and energy storage
High in energy and water-insoluble
In general, the less oxygen the molecule contains, the more energy it contains, then fats and oils have more energy than sugars and proteins (contain numerous hydroxyl atoms)2
Fats and oils have about 9 kcal (Cal) of energy per gram, twice as effective as compared to dry carbohydrates and proteins
“Fats and oils are stored “dry” in fat cells, but glycogen is hydrated by numerous water molecules”3
2 Bradford, M. et al Organic and Biological Chemistry. Saunders College Publishing, United States. p. 301
3 Ibid

11. Biological functions…
Fatty tissue serves a protective role
Help to cushion and protect organs from injury
Large amounts of fatty acids are required in animals
These are used in insulation against cold temperatures and energy source in animals that hibernate
Subcutaneous fat in humans also has an insulating role