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
Slide 3
2014 Pearson Education, Inc. Animation: Lipids
Slide 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
Slide 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
Slide 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
Slide 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
Slide 8
Figure 3-12 Synthesis of a triglyceride triglyceride fatty
acids glycerol
Slide 9
Figure 3-13a Fat Fat
Slide 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 CC bonds);
for example, beef fat
Slide 11
Figure 3-14a A fat A fat
Slide 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
Slide 13
Figure 3-14b An oil An oil
Slide 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
Slide 15
Figure 3-13b Wax Wax
Slide 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
Slide 17
Figure 3-15 Phospholipids fatty acid tails phosphate group
variable functional group glycerol backbone polar head
(hydrophilic) (hydrophobic)
Slide 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
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
Slide 23
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.