1. LIPIDS

2. 3.4 What Are Lipids?
Lipids are a diverse group of molecules that contain regions composed almost entirely of hydrogen and carbon
All lipids contain large chains of nonpolar hydrocarbons
Most lipids are therefore hydrophobic and water insoluble

3. Animation: Lipids

4. 3.4 What Are Lipids?
Lipids are diverse in structure and serve a variety of functions
They are used for energy storage
They form waterproof coverings on plant and animal bodies
They serve as the primary component of cellular membranes
Still others are hormones

5. 3.4 What Are Lipids? Lipids are classified into three major groups
Oils, fats, and waxes
Phospholipids
Steroids containing rings of carbon, hydrogen, and oxygen

6. 3.4 What Are Lipids?
Oils, fats, and waxes are lipids containing only carbon, hydrogen, and oxygen
Oils, fats, and waxes are made of one or more fatty acid subunits

7. 3.4 What Are Lipids?
Oils, fats, and waxes are lipids containing only carbon, hydrogen, and oxygen (continued)
Fats and oils
Are used primarily as energy-storage molecules, containing twice as many calories per gram as carbohydrates and proteins
Are formed by dehydration synthesis
Three fatty acids  glycerol  triglyceride

8. Figure 3-12 Synthesis of a triglyceride
glycerol
fatty acids
triglyceride 8

9. Figure 3-13a Fat
Fat 9

10. 3.4 What Are Lipids?
Oils, fats, and waxes are lipids containing only carbon, hydrogen, and oxygen (continued)
Fats that are solid at room temperature are saturated (the carbon chain has as many hydrogen atoms as possible, and mostly or all C–C bonds); for example, beef fat

11. Figure 3-14a A fat
A fat 11

12. 3.4 What Are Lipids?
Oils, fats, and waxes are lipids containing only carbon, hydrogen, and oxygen (continued)
Fats that are liquid at room temperature are unsaturated (with fewer hydrogen atoms, and many CC bonds); for example, corn oil
Unsaturated trans fats have been linked to heart disease

13. Figure 3-14b An oil
An oil 13

14. 3.4 What Are Lipids?
Oils, fats, and waxes are lipids containing only carbon, hydrogen, and oxygen (continued)
Waxes are highly saturated and solid at room temperature
Waxes form waterproof coatings such as on
Leaves and stems in plants
Fur in mammals
Insect exoskeletons
Waxes are also used to build honeycomb structures

15. Figure 3-13b Wax
Wax 15

16. 3.4 What Are Lipids?
Phospholipids have water-soluble “heads” and water-insoluble “tails”
These form plasma membranes around all cells
Phospholipids consist of two fatty acids  glycerol  a short polar functional group
They have hydrophobic and hydrophilic portions
The polar functional groups form the “head” and are water soluble
The nonpolar fatty acids form the “tails” and are water insoluble

17. Figure 3-15 Phospholipids
variable
functional
group
phosphate
group
polar head
glycerol
backbone
fatty acid tails
(hydrophilic)
(hydrophobic) 17

18. 3.4 What Are Lipids? Steroids contain four fused carbon rings
Steroids are composed of four carbon rings fused together with various functional groups protruding from them
Examples of steroids include cholesterol
Found in the membranes of animal cells
Component of male and female sex hormones
Makes up 2% of human brain
Excessive cholesterol contributes to cardiovascular disease

19. Figure 3-16 Steroids
Estrogen
Cholesterol
Testosterone 19

20. Triglycerides and Olestra
Building
Triglycerides and Olestra

21. Triglyceride

22. Olestra
Olestra is a large water insoluble sucrose polyester made of 6-8 fatty acids bonded to sucrose. The type and number of fatty acids determine the physical properties of Olestra The fatty acids come from edible oils such as cottonseed, corn, and soybean oils

23. Olestra is a food ingredient which is chemically prepared
Olestra is a food ingredient which is chemically prepared with similar properties of fats.
Olestra is a fat-substitute will sucrose backbone. As it is not absorbed, its calorific value is zero.
They are not absorbed in the intestines. This is due to their large size.
A tri-ester of fatty acid can be easily absorbed but a polymer of 6-8 fatty acids with a sucrose molecule as backbone is a large compound impossible to absorbed and metabolized.
This fat substitute is stable at higher temperatures also. It has zero saturated and trans fat but tastes like fat.
However, there are problems with this chemically synthesized compound too.
Many cases with digestive upset were observed as this molecule will directly excreted in stools because it is not absorbed in intestines. Also, vitamin and phyto-chemical losses occur. Olestra was produced by Olean company.

24. olestra