Download Lipids

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.‖
• extracted from cells using nonpolar organic solvents.
• natural components of cell membranes, fat-soluble
vitamins, and steroid hormones.
Lipids
There are 2 types of lipids;
• those that contain the structural component of a fatty acid;
and
• those that contain the structural component of a four
member steroid molecule.
Types of Lipids
The lipids that contain fatty acids are
• waxes,
• fats and oils (triacylglycerols),
• glycerophospholipids, and
• prostaglandins.
The types of lipids that do not contain fatty acid chains are
steroids.
Types of Fatty Acid Lipids
Learning Check
Which lipids contain the alcohol glycerol?
A. steroids and waxes
B. triacylglycerols and glycerophospholipids
C. sphingolipids and glycerophospholipids
D. glycerophospholipids and waxes
Solution
Which lipids contain the alcohol glycerol?
A. steroids and waxes
B. triacylglycerols and glycerophospholipids
C. sphingolipids and glycerophospholipids
D. glycerophospholipids and waxes
Answer is B. Triacylglycerols and glycerophospholipids
contain the alcohol glycerol.
Fatty Acids
Fatty acids
• contain long-chain
hydrocarbons with a
carboxylic acid.
• typically contain 12 to 18
carbon atoms.
• are insoluble in water.
• can be saturated or
unsaturated.
Fatty Acid Formulas
The formulas for fatty acids are written as
• condensed structural formulas.
• skeletal formulas.
Saturated Fatty Acids
Saturated fatty acids have
• only single C—C bonds.
• molecules that fit closely together in a
regular pattern.
• have properties similar to alkanes.
Saturated Fatty Acids
Unsaturated Fatty Acids
Unsaturated fatty acids
• have one or more double
bond.
• that are naturally occurring have one or more cis double
bond
insert picture of cis and trans fatty acid from top of pg 602
Monounsaturated Fatty Acids
Unsaturated fatty acids with one double bond are called
monounsaturated fatty acids.
Insert table 17.1 monounsaturated fatty acids.
Polyunsaturated Fatty Acids
Unsaturated fatty acids with more than one double bond are
called polyunsaturated fatty acids.
Insert table 17.1 polyunsaturated fatty acids.
Properties of Saturated
Fatty Acids
Saturated fatty acids
• fit closely together in
a regular pattern.
• are solids at room
temperature.
Properties of
Unsaturated Fatty Acids
Unsaturated fatty acids
• have ―kinks‖ in the
fatty acid chains.
• do not pack closely.
• are liquids at room
temperature.
―kinks‖ in
chain
Prostaglandins
Prostaglandins have
• 20 carbon atoms in their fatty acid chains.
• differ by the substituents attached to the 5-carbon ring.
Prostaglandins and
Physiological Effects
Prostaglandins have potent physiological effects.
• Some increase blood pressure.
• Some lower blood pressure.
• Some stimulate contractions and relaxation of smooth
muscle in the uterus during the birth process and menstrual
cycle.
When tissues are injured, arachidonic acid in the blood
is converted to PGE1 and PGF2 that produce
inflammation and pain in the area.
NSAIDs and Prostaglandins
Several nonsteroidal anti-inflammatory drugs (NSAIDs), such
as aspirin, block production of prostaglandins decreasing pain,
inflammation, and fever.
Insert Picture of arachidonic acid conversion, top page 605.
NSAIDs and Prostaglandins
Other NSAIDs include naproxen (Aleve and Naprosyn),
ketoprofen (Actron), and nabumetone (Relafen).
Long-term use of such products can result in liver, kidney, and
gastrointestinal damage.
Omega-3 and Omega-6
Fatty Acids
Fish and vegetable oils have high levels of unsaturated fats.
 In vegetable oils, they are mostly omega-6 with
the first
at C6.
Linoleic acid
 In fish oils, they are mostly omega-3 with the first
at C3.
CH3─CH2─(CH═CH─CH2)3─(CH2)6─COOH
1
3
Linolenic acid
Omega-6 and Omega-3 Fatty
Acids
Omega-3 Fatty Acids
Omega-3 fatty acids
• lower the tendency of blood platelets to stick together,
thereby reducing the possibility of blood clots.
• can help reduce risk of heart disease.
• are found in salmon, tuna, and herring.
Learning Check
Draw the condensed structural formulas for each of the fatty
acids with 10 carbon atoms that follow.
A. saturated
Learning Check
Draw the condensed structural formulas for each of the fatty
acids with 10 carbon atoms that follow.
B. monounsaturated omega-3
Learning Check
Draw the condensed structural formulas for each of the fatty
acids with 10 carbon atoms that follow.
C. monounsaturated omega-6
Solution
Draw the condensed structural formulas for each of the fatty
acids with 10 carbon atoms that follow.
A. saturated
CH3—CH2—CH2—CH2—CH2—CH2—CH2—CH2—CH2—COOH
B. monounsaturated omega-3
C. monounsaturated omega-6
Waxes
Waxes are
• esters of saturated fatty acids and long-chain alcohols each
containing 14 to 30 carbon atoms.
• coatings that prevent loss of water from leaves of plants.
Typical Waxes
Fats and Oils:
Triacylglycerols
Fats and oils are
• also called triacylglycerols.
• triesters of glycerol.
• produced by esterification.
• formed when the hydroxyl
groups of glycerol react with the
carboxyl groups of fatty acids.
• a major form of energy storage
for animals.
Insert picture of
polar bear pg 608
Triacylglycerols
In a triacylglycerol, glycerol forms ester bonds with three
fatty acids.
Insert structure top pg 608 as shown:
Formation of a
Triacylglycerol
• Most naturally occurring fats and oils are mixed
triacylglycerols that contain glycerol bonded by ester
bonds to two or three different fatty acids, typically
palmitic acid, linoleic acid, and stearic acid.
• One possible structure follows.
Learning Check
Draw the condensed structural formula for glyceryl
tripalmitoleate (tripalmitolein).
Solution
Draw the condensed structural formula for glyceryl
tripalmitoleate (tripalmitolein).
Fats and Oils
• Fats and oils are one of the three energy sources provided by
diet.
• Nutritionists recommend that less than 30% of the daily
dietary caloric intake by derived by fats.
• Fats provide more energy per gram than carbohydrates and
protein
• When calculating calories from fat, multiply by 9, for carbs
and protein multiple by 4.
Properties of Fats and Oils
A triacylglycerol that is usually called a fat
• is solid at room temperature.
• is prevalent in meats, whole milk, butter, and cheese.
A triacylglycerol that is usually called an oil
• is liquid at room temperature.
• is prevalent in plants, such as olive and safflower.
Oils with Unsaturated
Fatty Acids
Oils
• have more unsaturated fats.
• have cis double bonds that cause ―kinks‖
in the fatty acid chains.
• cannot pack triacylglycerol molecules as
closely together as in fats.
• are liquids at room temperature.
Triacylglycerol with
Unsaturated Fatty Acids
Unsaturated fatty
acid chains have
kinks that do not
allow close
packing, such as
those in olive oil.
Saturated and Unsaturated Fatty
Acids In Fats and Oils
Vegetable oils are liquids at room temperature because they
have a higher percentage of unsaturated fatty acids than do
animal fats.
Chemical Properties of
Triacylglycerols
The chemical reactions of triacylglycerols are similar
to those of alkenes and esters.
• In hydrogenation, double bonds in unsaturated fatty
acids react with H2 in the presence of a Ni or Pt
catalyst.
• In hydrolysis, ester bonds are split by water in the
presence of an acid, a base, or an enzyme.
Hydrogenation of
Glyceryl Trioleate
In a hydrogenation reaction, H2 adds across
the double bond to form a carbon–carbon single
bond.
Hydrogenation of Oils
The hydrogenation of oils
• converts double bonds to single bonds,
• adds hydrogen (H2) to the carbon atoms of double bonds,
• produces solids, such as margarine and shortening
Cis and Trans Fatty Acids
Unsaturated fatty acids can be
• cis with bulky groups on the same side of
• trans with bulky groups on opposite sides of
, or
.
Trans Fatty Acids and
Hydrogenation
Trans fatty acids
• are formed during hydrogenation when cis double bonds
are converted to an undesirable side product with a trans
double bond.
• in the body behave like saturated fatty acids.
• are estimated to make up 2–4% of our total calories.
The American Heart Association recommends the use of soft
margarine, which is only slightly hydrogenated and therefore
has fewer trans fatty acids.
Trans Fats
In vegetable oils,
• the unsaturated fats usually contain cis double bonds.
• during hydrogenation, some cis double bonds are
converted to trans double bonds (more stable), causing a
change in the fatty acid structure.
Formation of Trans Fats
Learning Check
Identify each statement as true (T) or false (F).
A. There are more unsaturated fats in vegetable oils.
B. Hydrogenation of oils converts some cis-double bonds to
trans-double bonds.
C. Animal fats have more saturated fats.
Solution
Identify each statement as true (T) or false (F).
T A. There are more unsaturated fats in vegetable oils.
T B. Hydrogenation of oils converts some cis-double
bonds to trans-double bonds.
T C. Animal fats have more saturated fats.