Unit-3 The Structure and Functionsof Lipids - Copy.ppt

Common Physical Properties of Lipids
 Soluble in non-polar organic solvents
 Contain C, H, O
 Sometimes N & P
 Includes fats and oils – mostly triglycerides
 Fat: solid at room temperature
 Oil: liquid at room temperature
 More highly reduced than CHO
 more energy

Lipids or Glucose for Energy?
H3C
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
O
OH
HC
CH
HC
CH
CH
CH2OH
O
HO
HO
OH
HO
More reduced state (more H bound to C)
 More potential for oxidation
Less reduced state (more O bound to C)
 Less potential for oxidation

Energy from Lipids
 Compared to carbohydrates, fatty acids
contain more hydrogen molecules per unit
of carbon, thus, they are in a more reduced
form
 Carbohydrates are partially oxidized so
they contain less potential energy (H+ and
e-) per unit of carbon

Functions and Properties
 Concentrated source of energy (9 kcal/gm)
 Energy reserve: any excess energy from
carbohydrates, proteins and lipids are
stored as triglycerides in adipose tissues
 Provide insulation to the body from cold
 Maintain body temperature
 Mechanical insulation
 Protects vital organs

 Electrical insulation
 Protects nerves, help conduct electro-chemical
impulses (myelin sheath)
 Supply essential fatty acids (EFA)
 Linoleic acid and linolenic acid
 Formation of cell membranes
 Phospholipids, a type of fat necessary for the
synthesis of every cell membrane (also
glycoproteins and glycolipids)

 Synthesis of prostaglandins from fatty acids
 Hormone-like compounds that modulates many
body processes

Immune system, nervous systems, and GI secretions

Regulatory functions: lower BP, blood clotting, uterine
contractions
 Helps to transport fat soluble vitamins
 Palatability /የሚጥም/and aroma/ሽታ፣መዓዛ/
 Flavor and taste for some species!
 The satiety/ጥጋብ/ value – help control
appetite
 Fullness; fats are digested slower

Fatty Acid Structure
H - C - ( C )n - C - OH
-
H
-
H
-
H
-
H
=
O
Carboxyl
group
Carbon
group(s
)
Methyl
group

Fatty Acids
 Building blocks for triglycerides and
phospholipids
 A chain of carbon and hydrogen
atoms with a carboxyl group at the
alpha end and a methyl group at the
omega end

Fatty Acids
 With a few exceptions, natural fatty
acids:
 Contain an even number of carbon atoms
 Arranged in an unbranched line
 Have a carboxyl group (-COOH) at one end
 Have a methyl group (CH3) at the other
end

Unit-3 The Structure and Functionsof Lipids - Copy.ppt

Fatty Acid Chain Length
 Short chain: 2 to 6 C (volatile fatty acids)
 Medium chain: 8 – 12 C
 Long chain: 14 – 24 C
 As chain length increases, melting point
increases
 Fatty acids synthesized by plants and
animals have an even number of carbons
 Mostly long chain
 16C to 18C fatty acids are most prevalent

Fatty Acid Saturation
 Saturated - no double bonds
 Unsaturated – contain double bonds
 Monounsaturated – one double bond
 Polyunsaturated - >1 double bond
 The double bond is a point of
unsaturation
 As number of double bonds
increases, melting point decreases

Saturated and Unsaturated Fatty
Acids Help Shape Foods

Saturated Fats
 All the chemical bonds between the carbon
are single bonds C-C-C-
 No double bonds
 No space for more H atoms; fully
“saturated”
 Solid at room temperature

Butter, shortening, lard, coconut oil, palm oil,
and fully hydrogenated vegetable oils

Poultry skin, whole milk

Mono-Unsaturated Fatty Acids
 Only one double bond
 Therefore, two H atoms can be added
 Liquid at room temperature
 Olive oil, canola oil, peanut oil
 Other sources: avocado, almonds,
cashews, pecans and sesame seeds

Poly-Unsaturated Fatty Acids
 Two or more double bonds
 Include omega-3 and omega-6 fatty acids
(essential fatty acids)
 Linolenic acid: omega 3 fatty acid
 Linoleic acid: omega 6 fatty acid
 Richest sources of poly-unsaturated fatty
acids include:
 Vegetable oils

Corn, sunflower, safflower, cotton seed oils

Saturation
 Unsaturated fatty acids
 Converted to saturated fatty acids by rumen
microbes
 More susceptible to rancidity

Oxidation of double bonds produces peroxides and free
radicals, which can cause damage to other compounds
 Antioxidants
 Vitamins E, C
 Carotenoids

Such as beta-carotene, lycopene
 Selenium

Fatty Acid Nomenclature
 Chain length
 Most fatty acids have an equal number of
carbons

Fish oil is rich in odd-numbered FAs
 Double bonds
 Number

Location from methyl or carboxyl end
 Degree of “saturation”
H3C
C
H2
C
H
C
H
C
H2
C
H
C
H
C
H2
C
H
C
H
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
O
OH

Fatty-acid Nomenclature
 Named according to
chain length
 C18
H3C
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
O
OH

 Named according to the number of
double bonds
 C18:0
H3C
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
O
OH
Common name:
Stearic acid

H3C
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H
C
H
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
O
OH
double bonds
 C18:1
Common name:
Oleic acid

H3C
C
H2
C
H2
C
H2
C
H2
C
H
C
H
C
H2
C
H
C
H
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
O
OH
double bonds
 C18:2
Common name:
Linoleic acid

H3C
C
H2
C
H
C
H
C
H2
C
H
C
H
C
H2
C
H
C
H
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
O
OH
double bonds
 C18:3
Common name:
Linolenic acid

 Named according to the
location of the first double bond from
the non-carboxyl end (count from the
methyl end)
 Omega system (e.g., omega 3, 3)
 n–system (e.g., n–3)
H3C
C
H2
C
H
C
H
C
H2
C
H
C
H
C
H2
C
H
C
H
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
O
OH

H3C
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H
C
H
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
O
OH
H3C
C
H2
C
H2
C
H2
C
H2
C
H
C
H
C
H2
C
H
C
H
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
O
OH
H3C
C
H2
C
H
C
H
C
H2
C
H
C
H
C
H2
C
H
C
H
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
O
OH
Omega 9 or n–9 fatty acid

 Named according to location of
H’s
 Cis or trans fatty acids
Cis-9-octadecenoic acid
(Oleic acid)
Trans-9-octadecenoic acid
(Elaidic acid)

C
H C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H3C
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H O
OH
C
H
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
O
OH
H3
C C
H 2
C
H 2
C
H 2
C
H 2
C
H 2
C
H 2
C
H 2
C
H

Isomers
 Geometrical isomers
due to double bond
 Cis

occurs naturally

bend in acyl chain
 Trans

Not as common

Found in
hydrogenated oils

Results from bacterial
synthesis
 In fats in ruminants!!

Straight acyl chains
 Chain branching

Straight

Synthesized by
mammals and plants
 Branched

Synthesized by
bacteria

Figure 5.5
Fatty Acids Vary in Shape
 Unsaturated fatty acids form two
different shapes

Melting Points
 Affected by chain length
 Longer chain = higher melting temp
Fatty acid: C12:0 C14:0 C16:0 C18:0 C20:0
Melting point: 44°C 58°C 63°C 72°C 77°C

Melting Points
 Affected by number of double bonds
 More saturated = higher melting temp
Fatty acid: C18:0 C18:1 C18:2 C18:3
Melting point: 72°C 16°C –5°C –11°C

Essential Fatty Acids
 Must be in diet
 Tissues can not synthesize
 Linoleic acid (18:2)

Omega-6-FA
 Linolenic acid (18:3)

Omega-3-FA
 Arachidonic (20:4)

Not found in plants!

Can be synthesized from C18:2 (linoleic acid) in most
mammals (except in cat)
 Essential nutrient in the diet of cats

Functions of Essential
Fatty Acids
 A component of the phospholipids in
cell membranes
 Precursor for prostaglandins:
arachidonic acid
 Important metabolic regulator
 Contraction of smooth muscle
 Aggregation of platelets
 Inflammation

Essential Fatty Acids
 Deficiency of essential fatty acid
intakes:
 Growth retardation
 Problems with reproduction
 Skin lesions
 Kidney and liver disorders

Simple Lipids or Homolipids
 Simple lipids are esters of fatty acid
linked with various alcohols.
 Fats and oils (triglycerides,
triacylglycerols)
 These esters of fatty acid have
glycerol, a trihydroxy alcohol. Fat is
solid at room temperature, while oil
is in liquid form.

 Triglycerides are abundant and constitute about
98 percent of all dietary lipids. The rest consists
of cholesterol, its esters and phospholipids.
 Unlike carbohydrates, which can be stored only
for a short time in the body, triglycerides are
stored in the body in large amounts as body fat,
which can last for years.
 An average man weighing about 70 kg, has at
least 10 to 20 percent of his body weight in
lipid, most of which is triacylglycerol.
 This is found in adipose (fat) tissue, as well as all
other organs of the body. Body fat is a reservoir
of chemical energy.

Waxes
 Waxes are long-chain saturated and
unsaturated fatty acid esters with
monohydroxy alcohols, which have high
molecular weight.
 Waxes are produced naturally by skin
glands as a protection, to keep it
lubricated, pliable, and water-proof. Wax
also covers hair, feathers, and wool.

Compound Lipids or Heterolipids
 Heterolipids are fatty acid esters with alcohol and
additional groups.
 Phospholipids (phosphatids)
 Phospholipids contain fatty acids, glycerol, nitrogen
bases, phosphoric acid, and other substituents.
 They are most abundant in cell membranes and
serve as structural components. They are not stored
in large quantities. As their name implies,
phospholipids contain phosphorus in the form of
phosphoric acid groups.
 Their molecular structure is polar, consisting of one
hydrophilic head group and two hydrophobic tails.

Glycolipids (cerebrosides)
 Glycolipids are fatty acids with carbohydrates and
nitrogen but without phosphoric acid. Glycolipids also
include some compounds like sulfolipids, gangliosides,
and sulfatids which are structurally-related.
 These cerebrosides are important constituents of the
brain and other tissues.
 They consist of at least one sugar unit, so they are also
called glycosphingosides. They are like phospholipids
because they have a hydrophobic region, with a polar
region and two long hydrocarbon tails.
 Like phospholipids, glycolipids form lipid bilayers that
are self-sealing and form the structure of cellular
membranes.

Derived Lipids
 These substances are derived by
hydrolysis from compound and
simple lipids. These fatty acids
include alcohols, mono- and
diglycerides, carotenoids, steroids,
and terpenes.

 Steroids
 The steroids are biological
compounds that are some of the
most studied types of fat. They
contain no fatty acids and unlike fats,
are nonsaponifiable (cannot be
hydrolyzed to yield soap).
Steroids

 Cholesterol
 Cholesterol is a well-studied lipid,
because of its strong correlation with
the incidence cardiovascular disease. It
is an important component of cell
membranes and plasma lipoproteins,
and is an important precursor of many
biologically important substances like
bile acids and steroid hormones. It is
abundant in nerve tissues and is
associated with gallstones.

 Dietary cholesterol is found in saturated fats of
animals (as butter and lard), but vegetable oils
do not contain cholesterol.
 Only a small portion of your body cholesterol
comes from the diet. Most of it is produced in
the body.
 Eating unsaturated fatty acids from vegetable
oil helps lower blood cholesterol levels by
reducing cholesterol synthesis in the body.
 However, eating saturated fats from animal fat
elevates blood cholesterol and triglycerides
and reduce the ratio of your good to bad
cholesterol.

Simple Lipids
 Neutral fats and oils
 Monoacyl glycerols (monoglycerides)
 Diacyl glycerols (diglycerides)
 Diglycerides found in plant leaves
 One fatty acid is replaced by a sugar (galactose)
 Triacyl glycerols (triglycerides)

Triglycerides found in seeds and
animal adipose tissue
 Triacyl glycerols (triglycerides)
 Lipid storage form

Where in the body? Adipocytes!!
 Most lipids consumed are triglycerides

Triglycerides
 Three fatty acids connected to a
glycerol backbone

Triglycerides
 Most common structure in dietary lipids
 Composed of one glycerol molecule and three fatty
acids connected by an ester bond (bond between an
alcohol and and organic acid)
 Fatty acids may be same or mixed
Glycerol
Fatty Acid
Fatty Acid
Fatty Acid

Caution:
High levels
in the
blood are a
risk factor
for heart
disease
Triglycerides
 Most common lipid in both foods and the
body
 Make up about 95% of lipids found in foods
 Functions

Add texture

Makes meats tender

Preserves freshness

Stores as adipose tissue
for energy

Most Common Fatty Acids in Di- and
Triglycerides
Fatty acid Carbon:Double bonds Double bonds
Myristic 14:0
Palmitic 16:0
Palmitoleic 16:1 Cis-9
Stearic 18:0
Oleic 18:1 Cis-9
Linoleic 18:2 Cis-9,12
Linolenic 18:3 Cis-9,12,15
Arachidonic 20:4 Cis-5,8,11,14
Eicosapentaenoic 20:5 Cis-5,8,11,14,17
Docosahexaenoic 22:6 Cis-4,7,10,13,16,19
CH3(CH2)nCOOH

Complex Lipids - Phospholipids
 Two primary types:
 Glycerophosphatides

Core structure is glycerol

Part of cell membranes, chylomicrons,
lipoproteins
 Sphingophosphatides

Core structure is sphingosine

Part of sphingomyelin

 Hydrophilic on one end; hydrophobic
on the other
 Make up the phospholipid bilayer in
the cell membrane
 Lecithin (a.k.a. phosphatidylcholine)

A major phospholipid in the cell membrane

Used as an emulsifier in foods
 Synthesized by the liver
Phospholipids
Portion of Figure 5.8

Phospholipids
 Structure:
 glycerol + 2 fatty acids + PO4
 PO4 = negatively charged
It’s just like a
penguin…
A head at one end
& a tail
at the other!

Phospholipids
 Hydrophobic or hydrophilic?
 fatty acid tails =
 PO4 head =
 split “personality”
interaction with H2O is
complex &very important! “repelled by water”
“attracted to water”
hydrophobic
hydrophillic

Phospholipids in water
 Hydrophilic heads “attracted” to H2O
 Hydrophobic tails “hide” from H2O
 can self-assemble into “bubbles”

bubble = “micelle”

can also form a phospholipid bilayer

early evolutionary stage of cell?
bilayer
water
water

Why is this important?
 Phospholipids create a barrier in water
 define outside vs. inside
 they make cell membranes!

Phospholipids’ Role in Cell
Membranes

Complex Lipids -
Phospholipids
 Glycerophosphatides resemble triglyceride
in structure except one of the fatty acids is
replaced by a compound containing a
phosphate group, or occasionally, nitrogen
 Most prevalent is lecithin

Phospholipids
 Significant use in feed industry as
emulsifiers
 Lipids form emulsion in water
 Phospholipid sources:
 Liver, egg yolk,
 Soybeans, wheat germ
 Peanuts

Complex Lipids -
Glycolipids
 Carbohydrate component in
structure
 Cerebrosides & gangliosides
 Medullary sheaths of nerves; white
matter of brain

Derived Lipids
 Prostaglandins
 Synthesized from arachidonic acid

Several metabolic functions
 Steroids
 Cholesterol, ergosterol, bile acids
 Terpenes
 Made by plants

Carotenoids, xanthophylls

Sterols
 Compounds with multi-ring structure
 Insoluble in water
 Present both in plant and animal foods
 Major sterol is cholesterol
 However, cholesterol is found only in animal
products (manufactured in liver)

High content in organ meats and egg yolk

Common Sterol Compounds
Stigmasterol
(a phytosterol)
Cholestero
l
(a sterol)
Vitamin D3
(cholecalciferol)
Testosterone
(a steroid
hormone)

 Major steroid in animal tissue
 Amphipathic with a polar head group
( -OH group at C3) and a non polar
hydrocarbon body
 Synthesized from acetyl Co A
 Two forms:
Free, esterified ( with a long chain fatyy acid)
 Melts at 150 C
 Insoluble in water but can be extracted from
tissue by cloroform, ether, benzene

Function of cholesterol
 In plasma membrane
 In lipoproteins
 Precursor of many other steroids:
a) Bile acids ( Cholic acid, taurocholic acid)
b) Steroid hormones ( male and female
sex hormones, progesterone,
adrenocortcal)

Cholesterol
 Important cell component
 animal cell membranes
 precursor of all other steroids

including vertebrate sex hormones
 high levels in blood may contribute to
cardiovascular disease

Cholesterol
helps keep
cell membranes
fluid & flexible
Important component of cell membrane

From Cholesterol  Sex Hormones
 What a big difference a few atoms can make!

Fatty Acid Metabolism
Fatty Acid Metabolism

Fatty Acid Synthesis
• Occurs mainly in liver and
adipocytes, in mammary glands
during lactation
• Occurs in cytoplasm
• FA synthesis and degradation occur
by two completely separate
pathways
• When glucose is plentiful, large
amounts of acetyl CoA are produced
by glycolysis and can be used for

Three stages of fatty acid
synthesis:
A. Transport of acetyl CoA into cytosol
B. Carboxylation of acetyl CoA
C. Assembly of fatty acid chain

A. Transport of Acetyl CoA to the
Cytosol
• Acetyl CoA from catabolism of
carbohydrates and amino acids is
exported from mitochondria via the
citrate transport system
• Cytosolic NADH also converted to
NADPH
• Two molecules of ATP are expended for
each round of this cyclic pathway

Sources of NADPH for Fatty Acid Synthesis
1. One molecule of NADPH is generated for each molecule of acetyl
CoA that is transferred from mitochondria to the cytosol (malic
enzyme).
2. NADPH molecules come from the pentose phosphate pathway.

B. Carboxylation of Acetyl CoA
Enzyme: acetyl CoA carboxylase
Prosthetic group - biotin
A carboxybiotin intermediate is formed.
ATP is hydrolyzed.
The CO2 group in carboxybiotin is transferred to acetyl CoA
to form malonyl CoA.
Acetyl CoA carboxylase is the regulatory enzyme.

C. The Reactions of Fatty Acid Synthesis
• Five separate stages:
(1) Loading of precursors via thioester
derivatives
(2) Condensation of the precursors
(3) Reduction
(4) Dehydration
(5) Reduction

During the fatty acid synthesis all intermediates are linked to the protein called acyl
carrier protein (ACP-SH), which is the component of fatty acyl synthase complex.
The pantothenic acid is a
component of ACP.
Intermediates in the
biosynthetic pathway are
attached to the
sulfhydryl terminus of
phosphopantotheine
group.

The elongation phase of fatty acid synthesis starts with the
formation of acetyl ACP and malonyl ACP.
Acetyl transacylase and malonyl transacylase catalyze these
reactions.
Acetyl CoA + ACP  acetyl ACP + CoA
Malonyl CoA + ACP  malonyl ACP + CoA

Acetyl ACP and
malonyl ACP react
to form acetoacetyl
ACP.
Enzyme -
acyl-malonyl ACP
condensing
enzyme.
Condensation reaction

Reduction
Acetoacetyl ACP is reduced to
D-3-hydroxybutyryl ACP.
NADPH is the reducing agent
Enzyme: -ketoacyl ACP
reductase

Dehydration
D-3-hydroxybutyryl ACP
is dehydrated to form
crotonyl ACP
(trans-2
-enoyl ACP).
Enzyme: 3-hydroxyacyl
ACP dehydratase

Reduction
The final step in the cycle
reduces crotonyl ACP to
butyryl ACP.
NADPH is reductant.
Enzyme - enoyl ACP
reductase.
This is the end of first
elongation cycle (first round).

In the second round
butyryl ACP condenses
with malonyl ACP to
form a C6--ketoacyl
ACP.
Reduction, dehydration,
and a second reduction
convert the C6--
ketoacyl ACP into a C6-
acyl ACP, which is
ready for a third round
of elongation.

• Rounds of synthesis continue until a
C16 palmitoyl group is formed
• Palmitoyl-ACP is hydrolyzed by a thioesterase
Final reaction of FA synthesis
Acetyl CoA + 7 Malonyl CoA + 14 NADPH + 14 H+
Palmitate + 7 CO2 + 14 NADP+
+ 8 HS-CoA + 6 H2O
Overall reaction of palmitate synthesis from acetyl
CoA and malonyl CoA

Fatty Acid Elongation and Desaturation
The common product of fatty acid synthesis is palmitate (16:0).
Cells contain longer fatty acids and unsaturated fatty acids they are
synthesized in the endoplasmic reticulum.
The reactions of elongation are similar to the ones seen with fatty
acid synthase (new carbons are added in the form of malonyl
CoA).
For the formation of unsaturated fatty acids there are various
desaturases catalizing the formation of double bonds.

(1)Activation of fatty acids takes place on
the outer mitochondrial membrane
(2) Transport into the mitochondria
(3) Degradation to two-carbon
fragments (as acetyl CoA) in the
mitochondrial matrix (b-oxidation
pathway)
Stages of fatty acid oxidation

(1) Activation of Fatty Acids
• Fatty acids are converted to CoA thioesters by acyl-
CoA synthetase (ATP dependent)
• The PPi released is hydrolyzed by a pyrophosphatase
to 2 Pi
• Two phosphoanhydride bonds (two ATP equivalents)
are consumed to activate one fatty acid to a thioester

• The carnitine shuttle
system.
• Fatty acyl CoA is first
converted to acylcarnitine
(enzyme carnitine
acyltransferase I (bound to
the outer mitochondrial
membrane).
• Acylcarnitine enters the
mitochondria by a
translocase.
• The acyl group is
transferred back to CoA
(enzyme - carnitine
2) Transport of Fatty Acyl CoA into Mitochondria

b-oxidation
 B-oxidation of palmitate (C16:0) yields 106 molecules
of ATP
 C 16:0-CoA + 7 FAD + 7 NAD+
+ 7 H20 + 7 CoA  8 acetyl-
CoA + 7 FADH2 + 7 NADH + 7 H+
2.5 ATPs per NADH = 17.5
1.5 ATPs per FADH2 = 10.5
10 ATPs per acetyl-CoA = 80
Total = 108 ATPs
 2 ATP equivalents (ATP AMP + PPi, PPi  2 Pi)
consumed during activation of palmitate to acyl-CoA
 Net yield = 106 ATPs

Ketone Bodies
• A special source of fuel and energy for certain tissues
• Produced when acetyl-CoA levels exceed the capacity of the
TCA cycle (depends on OAA levels)
• Under starvation conditions no carbos to produced
anpleorotic intermediates
• Some of the acetyl-CoA produced by fatty acid oxidation in
liver mitochondria is converted to acetone, acetoacetate and
-hydroxybutyrate
• These are called "ketone bodies"
• Source of fuel for brain, heart and muscle
• Major energy source for brain during starvation
• They are transportable forms of fatty acids!

Formation of
ketone bodies
Re-utilization of ketone bodies

Unit-3 The Structure and Functionsof Lipids - Copy.ppt

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