Transcript Lipids

BIOCHEMISTRY 1
BCM 201
CHAPTER 3
LIPIDS
Lipids
Types of Lipids
Fatty Acids
Chemical & physical Properties of Fatty acids
Fats and oils
Lipids classifications
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LIPIDS
• Class of biomolecule whose distinctive
characteristic is their solubility behavior.
• Insoluble in water, but soluble in organic
solvents including :diethyl ether, chloroform, methylene chloride
and acetone.( this is due its hydrophobic
nature )
Types of Lipids
• Lipids with fatty acids ( open chain forms)
Waxes
Fats and oils (triglycerides)
Phospholipids
Sphingolipids
Glycolipids
• Lipids without fatty acids ( cyclic forms)
Steroids
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Lipid : structure
1. Open chain
 Long nonpolar tail with polar head
 Saponifiable
2. Cylic forms/Fused Ring:
 Based on the steroid ring skeleton
Fatty acids
• A molecule with a carboxyl group as the
polar end and a hydrocarbon chain as the
hydrophobic end.
• Also been called Amphiphatic compounds
because the carboxyl group ( COOH ) is
hydrophilic and the hydrocarbon tail is
hydrophobic.
•
•
•
•
Long-chain carboxylic acids
Insoluble in water
Typically 12-18 carbon atoms (even number)
Some contain double bonds
• An unbranched –chain carboxylic acid, mostly
in even numbers of carbon.
Polar hydrophilic
group
Non polar
hydrophobic tail
Saturated and Unsaturated Fatty Acids
Saturated = C–C bonds
Unsaturated = one or more C=C bonds
COOH
palmitic acid, a saturated acid
COOH
palmitoleic acid, an unsaturated fatty acid
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General rules for the structures of
naturally occurring fatty acids
1. Most fatty acids have an even number of
carbon atoms.
2. The hydrocarbon chain is almost always
unbranced.
3. Most carbon-carbon bonds are
single;however ,fatty acids may contain
one,two, or more carbon-carbon double
bonds.
4. Double bonds are most cis.
5. For monounsaturated fatty acids,the double
bond is usually between carbon 9 and 10.
6. If more than one carbon-carbon double bond
is present they are not conjugated but are
separated by methylene unit.
• Degree of unsaturation refers to the number of
double bonds. The superscript indicates the position
of double bonds. Ex: Δ9 refers to double bond at ninth
carbons atom from the carbonyls ends.
Comparison between saturated and
unsaturated fatty acids
Properties of Unsaturated
Fatty Acids
Properties of Saturated
Fatty Acids
• Contain one or more
double C=C bonds
• Nonlinear chains do not
allow molecules to pack
closely
• Few interactions between
chains
• Low melting points
• Liquids at room
temperature
• Contain only single C–C
bonds
• Closely packed
• Strong attractions between
chains
• High melting points
• Solids at room temperature
Triacylglycerols
• Glycerol is a simple compound that contains
three hydroxyl groups.
• When all three of the alcohol groups form
ester linkages with fatty acids, the resulting
compound is a triacylglycerols.
• TAGs which are solids at room temperature
are rich in saturated acids and are called fats.
• TAGs which are liquids at room temperature
are rich in unsaturated acids and are called
oils.
examples : oil seeds include peanut butter,
corn, palm, olive and soybean.
Fats and Oils
Formed from glycerol and fatty acids
O
CH2 OH
CH
OH
CH2
OH
glycerol
HO C
O
+
(CH2)14CH3
HO C (CH2)14CH3
O
HO C
(CH2)14CH3
palmitic acid (a fatty acid)
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Triglycerides (triacylglcerols)
Esters of glycerol and fatty acids
ester bonds
O
CH2
O
C
(CH2)14CH3 + H2O
O
CH
CH2
O
O
C (CH2)14CH3
O
C
+ H 2O
(CH2)14CH3 +
H 2O
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Properties of Triglycerides
Hydrogenation
• Unsaturated compounds react with H2
• Ni or Pt catalyst
• C=C bonds
C–C bonds
Hydrolysis
• Split by water and acid or enzyme catalyst
• Produce glycerol and 3 fatty acids
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Hydrogenation
O
CH2
O
C
(CH2)5CH CH(CH2)7CH3
O
CH
CH2
O
O
C (CH2)5CH CH(CH2)7CH3
O
C
+ 3 H2
Ni
(CH2)5CH CH(CH2)7CH3
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Product of Hydrogenation
O
CH2
O
C
(CH2)14CH3
O
CH
CH2
O
O
C (CH2)14CH3
O
C
(CH2)14CH3
Hydrogenation converts double bonds in oils to single bonds. The solid products are
used to make margarine and other hydrogenated items.
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Butter
Margerine
• It is possible to convert back and forth between saturated
and unsaturated fats and oils, and commercially this is done
to achieve a certain texture. The fats tend to be solid at
room temperature, and the oils tend to be liquids at room
temperature.
• For some functions the liquid is more desirable, such as a
cooking oil. For other functions, such as spreading
margarine, the solid is more desirable, unless it is too solid.
• So food processing companies have found ways to partially
hydrogenate vegetable oils to make them more solidified.
It's also possible to dehydrogenate these solids to put
double bonds back in.
• The terms saturated, mono-unsaturated, and polyunsaturated refer to the number of hydrogens attached to
the hydrocarbon tails of the fatty acids as compared to the
number of double bonds between carbon atoms in the tail.
• Fats, which are mostly from animal sources, have all single
bonds between the carbons in their fatty acid tails, thus all
the carbons are also bonded to the maximum number of
hydrogens possible.
• Since the fatty acids in these triglycerides contain the
maximum possible amount of hydrogens, these would be
called saturated fats. The hydrocarbon chains in these fatty
acids are, thus, fairly straight and can pack closely together,
making these fats solid at room temperature.
• Oils, mostly from plant sources, have some double
bonds between some of the carbons in the
hydrocarbon tail, causing bends or “kinks” in the shape
of the molecules.
• Because some of the carbons share double bonds,
they’re not bonded to as many hydrogens as they
could if they weren’t double bonded to each other.
• Therefore these oils are called unsaturated fats.
Because of the kinks in the hydrocarbon tails,
unsaturated fats can’t pack as closely together, making
them liquid at room temperature.
• In unsaturated fatty acids, there are two ways the
pieces of the hydrocarbon tail can be arranged
around a C=C double bond.
• In cis bonds, the two pieces of the carbon chain
on either side of the double bond are either both
“up” or both “down,” such that both are on the
same side of the molecule.
• In trans bonds, the two pieces of the molecule
are on opposite sides of the double bond, that is,
one “up” and one “down” across from each other.
Saponification and Soap
• Hydrolysis with a strong base
• Triglycerides split into glycerol and the salts of fatty
acids
• The salts of fatty acids are “soaps”
• KOH gives softer soaps
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Saponification
O
CH2
O
C
(CH2)16CH3
O
CH
CH2
O
O
C
O
C
(CH2)16CH3 + 3 NaOH
(CH2)16CH3
CH2 OH
CH
CH2
O
+OH + 3 Na O C (CH2)14CH3
salts of fatty acids (soaps)
OH
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example
Learning Check L1
How would the melting point of stearic acid
compare to the melting points of oleic acid and
linoleic acid? Assign the melting points of –17°C,
13°C, and 69°C to the correct fatty acid. Explain.
stearic acid (18 C) saturated
oleic acid (18 C) one double bond
linoleic acid (18 C) two double bonds
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Solution L1
Stearic acid is saturated and would have a higher
melting point than the unsaturated fatty acids.
Because linoleic has two double bonds, it would
have a lower mp than oleic acid, which has one
double bond.
stearic acid mp 69°C
oleic acid mp 13°C
linoleic acid mp -17°C
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Phospholipids
• Is a fat derivatives, having hydrophobic and
hydrophilic domains.
• Also referred as phosphoglycerides.
• Its simple form, one glycerol bonded to two
fatty acids and a phosphate group.
• i) phosphotidic acid
• ii) phosphate group carrying one several
nitrogen-containing molecules, choline.
• A major component of the cell membranes.
• Phospholipids are always needed for the
formation of a stable bilayer structure.
• Examples of phospholipids include lecithin,
cephalins, phosphoinositides (in the brain),
and cardiolipin (in the heart)
Functions of phospholipids:
• Act as building blocks of the biological cell
membranes in virtually all organisms
• Participate in the transduction of biological
signals across the membrane.
• Act as efficient store of energy as with
triglycerides.
• Play an important role in the transport of fat
between gut and liver in mammalian digestion.
• An important source of acetylcholine which is the
most commonly occuring neurotransmitter
substance occuring in mammals.
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Waxes
• Complex mixtures of esters of long chain
carboxylic acids and long chain alcohols.
• Serve as protective coatings for both plants
and animals.
• In plants, they coats stems, leaves and fruit.
• In animals, they are found on fur, feathers,and
skin.
Sphingolipids
• Sphingolipids, like the phospholipis ,are
composed of a polar head group and two
nonpolar tails.
• The core of sphingolipids is either the long
chain amino alcohol,sphingosine or its N-acyl
derivative ( a ceramide ).
• Are found in plants and animals.
• Abundant in nervous system.( component of
nerve cell membrans.
Steroid
• A group of lipids that have fused ring structure
of 3 six membered rings,and 1 five-membered
ring.
• Steroids are nonpolar.
• The most abundant steroid is cholesterol.
• Some common examples of steroids are:
Vitamin D, cholesterol, estrogen and
cortisone.
Functions
• Steroids are used to increase muscle bulk and
strength and to enable longer and harder athletic
training sessions. Some users take steroids for
cosmetic (body image) reasons.
• Anti-inflammatory steroids (or corticosteroids)
can reduce swelling, pain, and other
manifestations of inflammation. Synthetic
steroids are used in a variety of therapies to
control respiratory problems, skin inflammation,
ease joint inflammations, and to treat blood
disorders.
• Steroids increase protein synthesis, promoting
growth of muscles and bones. They reduce
the recovery time needed between training
sessions and enable athletes to train more
intensively for longer periods. Anabolic
steroids increase muscle mass.
• Cholesterol is the precursor for all steroids.It is
a common component of animal cell
membranes .
• It functions to help stabilize the membrane.
Thus,it is crucial molecule in animals.
Steroid
Cell Membrane
• The membrane that surrounds the cytoplasm of a cell;
it is also called the plasma membrane or, in a more
general sense, a unit membrane. This is a very thin,
semifluid, sheet like structure made of four continuous
monolayers of molecules.
• The plasma membrane and the membranes making up
all the intracellular membranous organelles display a
common molecular architectural pattern of
organization, the unit membrane pattern, even though
the particular molecular species making up the
membranes differ considerably.
• All unit membranes consist of a bilayer of lipid
molecules, the polar surfaces of which are directed
outward and covered by at least one monolayer of
nonlipid molecules on each side, most of which are
protein, packed on the lipid bilayer surfaces and held
there by various intermolecular forces.
• Some of these proteins, called intrinsic proteins,
traverse the bilayer and are represented on both sides.
The segments of the polypeptide chains of these
transverse proteins within the core of the lipid bilayer
may form channels that provide low-resistance path
was for ions and small molecules to get across the
membrane in a controlled fashion.
• The best model to represent membranes is
fluid-mosaic model. S. jonathan Singer and
Garth Nicholson in 1972 suggested this model
,which consist of a lipid bilayer embedded
with proteins ,with some on the surface
(peripheral ) and others passing through the
entire bilayer ( integral ).
Fluid-mosaic model
Fluid-mosaic model
• Plasma membranes are primarily lipid bilayers with
associated proteins and glycolipids
– Cholesterol is also a major component of plasma
membranes
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ENDS