Transcript The Chemistry of Life 4
Chemistry 24.4
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24.4
Lipids
Before the invention of electric lighting, wax candles were a major source of lighting in homes. In this section, you will read more about waxes and similar compounds that make up the class of biomolecules known as lipids.
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24.4
Lipids > Triglycerides
Triglycerides
What physical property distinguishes lipids from other classes of biological molecules?
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24.4
Lipids > Triglycerides
Fats, oils, and other water-insoluble compounds are called
lipids.
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24.4
Lipids > Triglycerides
Natural fats and oils exist as triesters of glycerol with fatty acids, which are long-chain carboxylic acids (C 12 through C 24 ). This form of lipid is known as a
triglyceride
.
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24.4
Lipids > Triglycerides
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24.4
Lipids > Triglycerides Lipids tend to dissolve readily in organic solvents, such as ether and chloroform, rather than in highly polar solvents such as water. This property sets them apart from most biological substances such as carbohydrates and proteins.
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24.4
Lipids > Triglycerides
The hydrolysis of oils or fats by boiling with an aqueous solution of an alkali-metal hydroxide is called
saponification.
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24.4
Lipids > Triglycerides
A typical saponification reaction is shown below.
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24.4
Lipids > Triglycerides
Saponification is used to make soap.
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24.4
Lipids > Phospholipids
Phospholipids
How do phospholipid molecules arrange themselves in water?
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24.4
Lipids > Phospholipids Phospholipids
, or lipids that contain phosphate groups, are abundant in cells.
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24.4
Lipids > Phospholipids In water, phospholipids spontaneously form a spherical double layer, called a lipid bilayer, in which the hydrophobic tails of phospholipid molecules are sandwiched between two layers of hydrophilic heads.
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24.4
Lipids > Phospholipids
A cell membrane has a lipid bilayer structure.
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24.4
Lipids > Phospholipids
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24.4
Lipids > Waxes
Waxes
Waxes
are esters of long-chain fatty acids and long-chain alcohols.
• Waxes are also part of the lipid family.
• Waxes are low-melting, stable solids.
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24.4 Section Quiz.
Assess students’ understanding of the concepts in Section 24.3.
Continue to: Launch:
-or-
Section Quiz Slide 17 of 20
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24.4 Section Quiz
1. The class of substances called lipids includes a. proteins.
b. hydrocarbons.
c. soaps.
d. fats, oils, and waxes.
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24.4 Section Quiz
2. In water, phospholipids spontaneously form a. a solution in which the hydrophilic heads dissociate from the hydrophobic tails.
b. a single layer in which hydrophobic tails are hydrogen-bonded to hydrophilic heads.
c.
a double layer in which the hydrophobic tails are sandwiched between the hydrophilic heads.
d. a double layer in which the hydrophilic heads are sandwiched between the hydrophobic tails.
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24.4 Section Quiz
3. The selective absorption of nutrients across a cell membrane occurs in channels formed by a. lipids.
b. phospholipids.
c. proteins.
d. carbohydrates.
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