General organic and biological chemistry structures off life 5th CH17 lipids GOB structures 5th ed

Lecture Presentation

Chapter 17
Lipids

Karen C. Timberlake
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Chapter 17 Lipids
A clinical lipid specialist
• assesses a patient’s
current diet and
exercise program.
• diagnoses and
determines treatment
including dietary
changes.
• advises patients on the
use of medications that
lower lipid levels.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Chapter 17 Readiness

Core Chemistry Skills
• Writing Equations for Hydrogenation,
Hydration, and Polymerization (12.7)
• Naming Alcohols and Phenols (13.1)
• Naming Carboxylic Acids (16.1)
• Hydrolyzing Esters (16.5)

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


17.1 Lipids
Lipids are
• biomolecules that contain fatty
acids or a steroid nucleus.
• soluble in organic solvents but
not in water.
• named for the Greek word lipos,
which means “fat.”
• an important feature in cell
membranes, fat-soluble vitamins,
and steroid hormones.

Steroid Nucleus

Learning Goal Describe the classes of lipids.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Types of Lipids
Lipids are characterized by their
structures:
Lipids such as
• waxes,
• triacylglycerols,
• glycerophospholipids, and
• sphingolipids
are esters that can be
hydrolyzed to give fatty acids
and other molecules.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Lipids Containing Glycerol
Triacylglycerols and glycerophospholipids contain the
alcohol glycerol.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.

Lipids Containing Sphingosine
Sphingolipids contain the amino alcohol sphingosine.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Lipids Containing Sphingosine
Steroids, which have a completely different structure, do not
contain fatty acids and cannot be hydrolyzed. They are
characterized by the steroid nucleus of four fused carbon rings.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


General Structure of Lipids

Lipids are naturally occurring compounds in cells and tissues.
They are soluble in organic solvents but not in water.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.

Study Check
Lipids are characterized by presence of fatty acids or
a steroid nucleus. Which type is described by the
following?
A. contain a fused four-membered
ring system
B. contain long carbon chains
C. include carboxyl groups

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Solution
Lipids are characterized by presence of fatty acids or
a steroid nucleus. Which type is described by the
following?
A. contain a fused four-membered
ring system

steroids

B. contain long carbon chains

fatty acids

C. include carboxyl groups

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

fatty acids

© 2016 Pearson Education, Inc.


Study Check
Which of the following is NOT a characteristic
of lipids?
A. may contain a carboxylic acid group
B. may contain a four-ring structure
C. soluble in water
D. mostly nonpolar

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Solution
Which of the following is NOT a characteristic
of lipids?
A. may contain a carboxylic acid group
B. may contain a four-ring structure
C. soluble in water
D. mostly nonpolar

The answer is C. Lipids are nonpolar and therefore
are NOT soluble in water.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


17.2 Fatty Acids
We might think of saturated fatty
acids as chips with regular
shapes that stack closely
together in a can.
Similarly, irregularly shaped
chips would be like unsaturated
fatty acids that do not fit closely
together.
Learning Goal Draw the condensed or line-angle
structural formula for a fatty acid and identify it as
saturated or unsaturated.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.

17.2 Fatty Acids
Fatty acids, the simplest type of lipids, are
• long, unbranched carbon chains with a carboxylic acid
group at the end.
• typically 12–18 carbon atoms long.
• insoluble in water because of the long carbon chain.
• saturated when they do not contain C C double
bonds in the carbon chain.
• unsaturated when they contain C C double bonds in
the carbon chain.
Core Chemistry Skill Identifying Fatty Acids
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Drawing Fatty Acids
• In a line-angle structural formula of a fatty acid, the ends and
bends of the line are the carbon atoms.
• The structural formula of lauric acid can be drawn in
several forms.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.

Saturated Fatty Acids
Fatty acids can be saturated, with only C — C single
bonds in the carbon chain.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Monounsaturated Fatty Acids
Fatty acids can be monounsaturated, with only one
double C     C bond in the carbon chain.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Polyunsaturated Fatty Acids
Fatty acids can be polyunsaturated, with at least two
double C     C bonds in the carbon chain.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.

Cis and Trans Unsaturated Fatty Acids
• Unsaturated fatty acids can be drawn as cis and trans isomers.
• Oleic acid is a monounsaturated fatty acid found in olives, with one
double bond at carbon 9.
• The trans isomer of oleic acid is called elaidic acid and has a
straight chain without a kink.

Almost all naturally occurring unsaturated fatty acids have one or more
cis double bonds.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Essential Fatty Acids
Humans
• are capable of synthesizing some fatty acids from
carbohydrates or other fatty acids.
• cannot synthesize sufficient amounts of
polyunsaturated fatty acids such as linoleic acid,
linolenic acid, and arachidonic acid.
Because these polyunsaturated fatty acids must be
obtained from the diet, they are known as essential
fatty acids.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.

Properties of Saturated Fatty Acids
Saturated fatty acids
• contain only single C — C bonds and fit close
together in a regular pattern, with strong
dispersion forces between carbon chains.
• require a significant amount of energy and high
temperatures to separate and melt.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Properties of Saturated Fatty Acids
In unsaturated fatty
acids, cis double bonds
cause the carbon chain
to bend or kink, giving
the molecules an
irregular shape and
thus allowing fewer
interactions between
molecules.
The reduced interactions in fatty
acids with cis bonds reduce the
melting point of the molecules.
General, Organic, and Biological Chemistry: Structures of Life, 5/e

Karen C. Timberlake

© 2016 Pearson Education, Inc.


Study Check
Consider the condensed structural formula for vaccenic acid.

A. Why is this molecule an acid?
B. How many total carbon atoms are in vaccenic acid?
C. Is this a saturated, monounsaturated, or polyunsaturated
fatty acid?
D. Is it likely to be a solid or liquid at room temperature?
E. Would it be soluble in water?
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.