Ch.15 Lipids

Timberlake - Chemistry: An Introduction to General, Organic, and Biological Chemistry 13th Edition

Timberlake13th EditionChemistry: An Introduction to General, Organic, and Biological ChemistryISBN: 9780134421353Not the one you use?Change textbook

Timberlake 13th Edition

Ch.15 Lipids

Problem 5

Chapter 15, Problem 5

Describe some similarities and differences in the structures of a saturated fatty acid and an unsaturated fatty acid.

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A saturated fatty acid has a hydrocarbon chain where all the carbon-carbon bonds are single bonds. This means the chain is fully 'saturated' with hydrogen atoms.

An unsaturated fatty acid contains one or more carbon-carbon double bonds in its hydrocarbon chain. These double bonds reduce the number of hydrogen atoms attached to the carbon chain.

Both saturated and unsaturated fatty acids have a carboxylic acid group (-COOH) at one end of the molecule, which is a common feature of all fatty acids.

The presence of double bonds in unsaturated fatty acids introduces kinks or bends in the hydrocarbon chain, making them less tightly packed compared to the straight chains of saturated fatty acids.

Saturated fatty acids are typically solid at room temperature (e.g., butter), while unsaturated fatty acids are usually liquid at room temperature (e.g., olive oil) due to differences in molecular packing.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Fatty Acid Structure

Fatty acids are carboxylic acids with long hydrocarbon chains. They consist of a hydrophilic (water-attracting) carboxyl group (-COOH) at one end and a hydrophobic (water-repelling) hydrocarbon tail. The length and saturation of the hydrocarbon chain influence the physical properties of the fatty acid.

Saturation

Saturation refers to the presence of double bonds between carbon atoms in the fatty acid chain. Saturated fatty acids have no double bonds, resulting in straight chains that pack tightly together, while unsaturated fatty acids contain one or more double bonds, causing kinks that prevent tight packing and lead to a liquid state at room temperature.

Physical Properties

The structural differences between saturated and unsaturated fatty acids lead to distinct physical properties. Saturated fatty acids are typically solid at room temperature due to their straight chains, while unsaturated fatty acids are usually liquid, which affects their roles in biological systems and their impact on health.

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02:54

Physical Properties Concept

Related Practice

Textbook Question

Which of the following solvents might be used to dissolve an oil stain?

a. water

b. CCl₄

c. diethyl ether

d. benzene

e. NaCl solution

Textbook Question

Draw the line-angle formula for each of the following fatty acids:

a. palmitic acid

Textbook Question

Stearic acid and linoleic acid each have 18 carbon atoms. Why does stearic acid melt at 69 °C but linoleic acid melts at –5 °C?

Textbook Question

Lipids are not soluble in water. Are lipids polar or nonpolar molecules?

Textbook Question

For each of the following fatty acids, give the shorthand notation for the number of carbon atoms and double bonds, and classify as saturated, monounsaturated, or polyunsaturated:

a. lauric acid

Textbook Question

What are some functions of lipids in the body?