Chemistry 121(01) Winter 2010-11
Introduction to Organic Chemistry and Biochemistry
Instructor Dr. Upali Siriwardane (Ph.D. Ohio State)
E-mail: upali@chem.latech.edu
Office: 311 Carson Taylor Hall ; Phone: 318-257-4941;
Office Hours: MWF 8:00 am - 10:00 am;
TT 9:00 – 10:00 am & 1:00-2:00 pm.
December 17, 2010 Test 1 (Chapters 12-13)
January 19, 2011 Test 2 (Chapters 14,15 & 16)
February 7, 2011 Test 3(Chapters 17, 18 & 19)
February 23, 2011 Test 4 (Chapters 20, 21 & 22)
February 24, 2011
Comprehensive Make Up Exam:
Chemistry 121 Winter 2011 LA Tech
19-1
Chapter 19. Lipids
Sections
Chemistry 121 Winter 2011 LA Tech
19-2
Chapter 19
19.1 Structure and Classification of Lipids
19.2 Fatty Acids: Lipid Building Blocks
19.3 Physical Properties of Fatty Acids
19.4 Energy-Storage Lipids: Triacylglycerols
19.5 Dietary Considerations and Triacylglycerols
19.6 Chemical Reactions of Triacylglycerols
19.7 Membrane Lipids: Phospholipids
19.8 Membrane Lipids: Sphingoglycolipids
19.9 Membrane Lipids: Cholesterol
19.10 Cell Membranes
19.11 Emulsification Lipids: Bile Acids
19.12 Messenger Lipids: Steroid Hormones
19.13 Messenger Lipids: Eicosanoids
19.14 Protective-Coating Lipids: Biological Waxes
Chemistry at a Glance: Types of Lipids and How They Function
Chemical Connections: The Fat Content of Tree Nuts and Peanuts;
Artificial Fat Substitutes; The Cleansing Action of Soap; Trans Fatty
Acids and Blood Cholesterol Levels; Steroid Drugs in Sports; The Mode
of Action for Anti-Inflammatory Drugs
Chemistry 121 Winter 2011 LA Tech
19-3
Lipids
A heterogeneous class of naturally occurring
organic compounds classified together on the
basis of common solubility properties
• insoluble in water
• soluble in aprotic organic solvents including diethyl
ether, dichloromethane, and acetone
Lipids include
•
•
•
•
•
•
Waxes
triglycerides
phospholipids
Prostaglandins
cholesterol, steroid hormones, and bile acids
fat-soluble vitamins
Chemistry 121 Winter 2011 LA Tech
19-4
Structure and Classification of Lipids
Lipids that are ester or amides of fatty acids:
Waxes – are carboxylic acid esters where both are carboxylic acid esters where both
R groups are long straight hydrocarbon chain. R groups are long straight hydrocarbon
chain.
Performs external protective functions. Performs external protective functions.
Triglycerides– are carboxylic acid are carboxylic acid triesters of
Glycerols . They are a major source of biochemical energy.
Glycolipids – amides derived from sphingosine, contain polar carbohydrate groups. On the
cell surface, they connect with intracellular messengers.
Glycerophopholipids – triesters of glycerols that contain charged phosphate diesters. They
help to control the flow of molecules into and out of cells.
Sphingomyelins – amides derived from an amino alcohol, also contain charged amino
alcohol, phosphate diester groups. They are essential to the structure of cell membranes.
Lipids that are not esters or amides:
Steroids – They performs various functions They performs various functions
such as hormones and contributes to the structure of cell membranes.
Eicosanoids – They are carboxylic acids that are a special type of intracellular chemical
Messengers.
Chemistry 121 Winter 2011 LA Tech
19-5
Wax
esters are fatty acids esterified to long-chain saturated or monoenoic (one double bond)
alcohols.
They are carboxylic acid esters where both are carboxylic acid esters where both
R groups are long straight hydrocarbon chain. R groups are long straight hydrocarbon
chain.
They performs external protective functions. Performs external protective functions.
O
Beeswax
CH3(CH2)24
O
(CH2)29CH3
Spermaciti: sperm whale wax
O
CH3(CH2)14
Chemistry 121 Winter 2011 LA Tech
O
(CH2)15CH3
19-6
Spermaceti source
Carnauba wax source
Bee’s wax
Chemistry 121 Winter 2011 LA Tech
19-7
Triglycerides
H2C O
CH2OH
CHOH
O
RCOOH
HC O
CH2OH
Glycerol
O
C O
H2
O Saturated Fat or Oil
Chemistry 121 Winter 2011 LA Tech
19-8
Properties of Fats and Oils
Oils: A mixture of triglycerides that is liquid
because it contains a high proportions of unsaturated
fatty acids.
Fats : A mixture of triglycerides that is solid because it
contains a high proportions of saturated fatty acids.
Chemistry 121 Winter 2011 LA Tech
19-9
Physical properties of Triglycerides
Depends on their fatty acid components
• melting point increases as the number of carbons in
their hydrocarbon chains increases and as the number
of double bonds decreases
• triglycerides rich in unsaturated fatty acids are
generally liquid at room temperature and are called oils
• triglycerides rich in saturated fatty acids are generally
semisolids or solids at room temperature and are
called fats
Chemistry 121 Winter 2011 LA Tech
19-10
Triglycerides
The lower melting points of triglycerides rich in
unsaturated fatty acids are related to differences
in their three-dimensional shape
• hydrocarbon chains of saturated fatty acids can lie
parallel with strong dispersion forces between their
chains; they pack into well-ordered, compact
crystalline forms and melt above room temperature
• because of the cis configuration of the double bonds in
unsaturated fatty acids, their hydrocarbon chains have
a less ordered structure and dispersion forces between
them are weaker; these triglycerides have melting
points below room temperature
Chemistry 121 Winter 2011 LA Tech
19-11
Reduction of Triglycerides
• the process of converting fats to oils is called
hardening and involves catalytic reduction of some or
all of an oil’s carbon-carbon double bonds
• in practice, the process is controlled to produce a fat of
a desired consistency
• the resulting fats are sold for cooking (Crisco, Spry,
and others)
• margarine and other butter substitutes are produced by
partial hydrogenation of polyunsaturated oils derived
from corn, peanuts, and soybeans
• because catalytic hydrogenation is to some degree
reversible, hardening results in the isomerization of
some cis-fatty acids to trans-fatty acids; trans fatty
acids are to be avoided as much as possible
Chemistry 121 Winter 2011 LA Tech
19-12
Triglycerides
An ester of glycerol with three fatty acids
O
O CH2 OCR
R'COCH O
1 . NaOH, H2 O
CH2 OCR'' 2 . HCl, H2 O
A triglyceride
Chemistry 121 Winter 2011 LA Tech
CH2 OH
HOCH
CH2 OH
RCOOH
+
R'COOH
R''COOH
1,2,3-Propanetriol Fatty acid s
(Glycerol, glycerin )
19-13
Soaps and Detergents
Natural soaps are prepared by boiling lard or other
animal fat with NaOH, in a reaction called
saponification (Latin, sapo, soap)
O
O CH2 OCR
sap on ification
RCOCH O + 3 NaOH
CH2 OCR
A triglyceride
Chemistry 121 Winter 2011 LA Tech
CH2 OH
CHOH
O
+
-
3RCO Na
+
CH2 OH
Sodium soaps
1,2,3-Propanetriol
(Glycerol; glycerin)
19-14
Soaps and Detergents
Soaps clean by acting as emulsifying agents
• the long hydrophobic hydrocarbon chains of soaps are
insoluble in water and tend to cluster in such a way as
to minimize their contact with water
• the polar hydrophilic carboxylate groups tend to
remain in contact with the surrounding water
molecules
• driven by these two forces, soap molecules
spontaneously cluster into micelles
• Micelle: a spherical arrangement of organic molecules
in water clustered so that their hydrophobic parts are
buried inside the sphere and their hydrophilic parts are
on the surface of the sphere and in contact with water
Chemistry 121 Winter 2011 LA Tech
19-15
Soaps and Detergents
• when soap is mixed with water-insoluble grease, oil,
and fat stains, the nonpolar parts of the soap micelles
“dissolve” nonpolar dirt molecules and they are carried
away in the polar wash water
Chemistry 121 Winter 2011 LA Tech
19-16
Soaps
Soaps form water-insoluble salts when used in
water containing Ca(II), Mg(II), and Fe(III) ions
(hard water)
2 CH3 (CH2 ) 1 4 COO- Na+
+ Ca2 +
A sodiu m s oap
(soluble in w ater as micelles)
-
[CH3 (CH2 ) 1 4 COO ] 2 Ca
2+ +
+
2 Na
Calcium salt of a fatty acid
(insolub le in w ater)
Chemistry 121 Winter 2011 LA Tech
19-17
Synthetic Detergents
The design criteria for a good detergent are
• a long hydrocarbon tail of 12 to 20 carbons
• a polar head group that does not form insoluble salts
with Ca(II), Mg(II), or Fe(III) ions
• the most widely used synthetic detergents are the
linear alkylbenzenesulfonates (LAS)
CH3 (CH2 ) 1 0 CH2
Dodecylben zene
1 . H2 SO4
2 . NaOH
CH3 (CH2 ) 1 0 CH2
-
SO3 Na
+
Sod ium 4-dodecylbenzenes ulfon ate
(an an ion ic detergent)
• also added to detergent preparations are foam
stabilizers, bleaches, and optical brighteners
Chemistry 121 Winter 2011 LA Tech
19-18
Fatty Acids
A long, unbranched chain carboxylic acid
• nearly all have an even number of carbon atoms, most
between 12 and 20, in an unbranched chain
• the three most abundant are palmitic acid (16:0),
stearic acid (18:0), and oleic acid (18:1)
• in most unsaturated fatty acids, the cis isomer
predominates; the trans isomer is rare
• unsaturated fatty acids have lower melting points than
their saturated counterparts; the greater the degree of
unsaturation, the lower the melting point
Chemistry 121 Winter 2011 LA Tech
19-19
Fatty Acids
The most abundant fatty acids
Carb on Atoms /
D ouble Bond s Stru cture
Saturated Fatty Acids
12:0
CH3 ( CH2 ) 1 0 COOH
14:0
16:0
CH3 ( CH2 ) 1 2 COOH
18:0
CH3 ( CH2 ) 1 4 COOH
CH3 ( CH2 ) 1 6 COOH
20:0
CH3 ( CH2 ) 1 8 COOH
Common
Name
mp
(°C)
lau ric acid
44
myris tic acid
palmitic acid
58
63
stearic acid
70
arach idic acid
77
Unsatu rated Fatty Acid s
16:1
CH3 ( CH2 ) 5 CH=CH(CH2 ) 7 COOH
18:1
CH3 ( CH2 ) 7 CH=CH(CH2 ) 7 COOH
16
18:2
-5
18:3
palmitoleic acid
oleic acid
CH3 ( CH2 ) 4 (CH=CHCH2 ) 2 ( CH2 ) 6 COOH lin oleic acid
CH3 CH2 (CH=CHCH2 ) 3 ( CH2 ) 6 COOH
lin olen ic acid
-11
20:4
CH3 ( CH2 ) 4 (CH=CHCH2 ) 4 ( CH2 ) 2 COOH arach idonic acid
-49
Chemistry 121 Winter 2011 LA Tech
1
19-20
Saturated Fatty Acids
Chemistry 121 Winter 2011 LA Tech
19-21
Saturated/Unsturated fatty acids
Chemistry 121 Winter 2011 LA Tech
19-22
Unsaturated Fatty Aicds
Chemistry 121 Winter 2011 LA Tech
19-23
Saturated/Unsturated fatty acids
Chemistry 121 Winter 2011 LA Tech
19-24
Saturated/Unstaureated Mixtures
Chemistry 121 Winter 2011 LA Tech
19-25
Fatty Acids
the greater the degree of unsaturation the lower the
melting point
COOH Stearic acid (18:0)
(mp 70°C)
COOH Oleic acid (18;1)
(mp 16°C)
COOH Linoleic acid (18:2)
(mp-5°C)
COOH Lin olen ic acid (18:3)
(mp -11°C)
Chemistry 121 Winter 2011 LA Tech
19-26
Unsaturated triglyceride
Chemistry 121 Winter 2011 LA Tech
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What are "Omega" series fatty acids?
Scientists differentiate fatty acids by the
characteristics of their molecules. The two
principal essential fatty acids are Omega-6
(n-6) series and the Omega-3(n-3) series. The
number indicates the position of the first double
carbon bond when counting from a specified end
of the molecule.
Chemistry 121 Winter 2011 LA Tech
19-28
Essential Fatty Acids
Fatty acids that cannot be produced by the body
and are necessary for proper metabolism. The
OMEGA 6 and OMEGA 3 fatty acids are referred
to as Essential Fatty Acids (EFA).
Chemistry 121 Winter 2011 LA Tech
19-29
Phospholipids
Phospholipids are the second most abundant
group of naturally occurring lipids
• they are found almost exclusively in plant and animal
membranes, which typically consist of 40% to 50%
phospholipids and 50% to 60% proteins
• the most abundant phospholipids are derived from
phosphatidic acid, a molecule in which glycerol is
esterified with two fatty acids and one phosphoric acid
• further esterification with a low-molecular weight
alcohol gives a phospholipid
• the three most abundant fatty acids in phosphatidic
acids are palmitic acid (16:0), stearic acid (18:0), and
oleic acid (18:1)
Chemistry 121 Winter 2011 LA Tech
19-30
Phospholipids
Phosphate(PO4 )-containing molecules with
structures related to the triglycerides are aclled
Glycerophopholipids
E.g. Phosphatidycholine (lecithin)
Chemistry 121 Winter 2011 LA Tech
19-31
Examples of glycerophospholipids
Name
Phosphatidyl choline (lecithin)
Phosphatidyl ethanolamine (cephalin)
Chemistry 121 Winter 2011 LA Tech
19-32
Phospholipids
A phosphatidate and a phospholipid
O
nonp olar
hydrocarbon
tails
A p hosph atidate
O CH2
O CH
O
CH2 O-P-O
O
OO
A p hosph olip id
Chemistry 121 Winter 2011 LA Tech
polar head
group s
O CH2
O CH
O
CH2 -O-P-OCH2 CH2 N(CH3 ) 3
O
O
19-33
Phospholipids
Chemistry 121 Winter 2011 LA Tech
19-34
Phosphatidycholine (lecithin)
Chemistry 121 Winter 2011 LA Tech
19-35
Phospholipids
• low-molecular weight alcohols in phospholipids
N ame and Fo rmul a
N ame of Pho spho li pid
ethano lami ne
HOCH2 CH2 NH2
cho li ne
pho sphatidy leth ano lami ne
(ceph al in)
+
HOCH2 CH2 N(CH3 ) 3
seri ne
pho sphatidy lcho li ne
(lecithin)
-
HOCH2 CHCOO
NH3
+
i no sito l
HO
ph osphatidy lseri ne
OH
HO
HO
Chemistry 121 Winter 2011 LA Tech
OH phosp hatid yl ino sitol
OH
19-36
Lipid Bilayer
When placed in aqueous solution, phospholipids
spontaneously form a lipid bilayer
• polar head groups lie on the surface, giving the bilayer
an ionic coating
• nonpolar fatty acid hydrocarbon chains lie buried
within the bilayer
This self-assembly is driven by two noncovalent
forces
• hydrophobic effects, which result when nonpolar
hydrocarbon chains cluster to exclude water molecules
• electrostatic interactions, which result when polar head
groups interact with water and other polar molecules in
the aqueous environment
Chemistry 121 Winter 2011 LA Tech
19-37
Plasma membrane
Planar lipid bilayers
Biological membranes are bilipid layers .
In a real cell the membrane phospholipids create a
spherical three dimensional lipid
bilayer shell around the cell. However, they are
often represented two-dimensionally as:
Passive tranport
Active transport
Chemistry 121 Winter 2011 LA Tech
19-38
Biological Membranes
Fluid mosaic model: a biological membrane
consists of a phospholipid bilayer with proteins,
carbohydrates, and other lipids embedded on the
surface and in the bilayer
• fluid signifies that the protein components of
membranes “float” in the bilayer and can move freely
along the plane of the membrane
• mosaic signifies that the various components of the
membrane exist side by side, as discrete units rather
than combining to form new molecules and ions
Chemistry 121 Winter 2011 LA Tech
19-39
Fluid-Mosaic Model
Chemistry 121 Winter 2011 LA Tech
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Prostaglandins
Essential fatty acids in the cell membranes
produce prostaglandins.
Prostaglandins regulate bodily functions in the
heart, kidneys, liver, lungs, brain,
nerves and the immune system.
Chemistry 121 Winter 2011 LA Tech
19-41
Types of Prostaglandins
In human beings, there are three families of
prostaglandins, each of which is derived
from a different fatty acid.
Prostaglandin PG
PGE1
PGF1
PGE2
PGF2
Eicosanoids
Thromboxane A2
Leukotriene B4
Chemistry 121 Winter 2011 LA Tech
19-42
Prostaglandins
Prostaglandins: a family of compounds that have
the 20-carbon skeleton of prostanoic acid
9
7
5
1
3
8
6
4
2
12
14
16
18
CO2 H
10
11
13
15
17
19
20
Pros tanoic acid
Chemistry 121 Winter 2011 LA Tech
19-43
Prostaglandins
Prostaglandins are not stored in tissues as such,
but are synthesized from membrane-bound 20carbon polyunsaturated fatty acids in response to
specific physiological triggers
• one such polyunsaturated fatty acid is arachidonic acid
9
8
COOH
13
11 12
14
15
Arachidonic acid
Chemistry 121 Winter 2011 LA Tech
19-44
Prostaglandins
• among the prostaglandins synthesized biochemically
from arachidonic acid are
O
HO
9
9
COOH
HO
11
COOH
15
OH
PGE2
Chemistry 121 Winter 2011 LA Tech
HO
11
15
OH
PGF2
19-45
Prostaglandins
• the observation that PGF2 stimulates contractions of
uterine smooth muscle led to the development of
synthetic PGFs that can be used for therapeutic
abortions
extra methyl group
at carbon-15
HO
HO
9
9
COOH
COOH
HO
11
15
HO
HO H
PGF2 
Chemistry 121 Winter 2011 LA Tech
11
15
HO CH3
Carb op rost
(15S)-15-Meth yl-PGF2 
19-46
Prostaglandins
• the PGE1 analog, misoprostol, is used to prevent the
ulceration associated with the use of aspirin-like
NSAIDs
O
O
COOH
HO
15 16
HO
HO H
PGE1
Chemistry 121 Winter 2011 LA Tech
COOCH3
HO
15
CH3
16
Misopros tol
19-47
Eicosanoids
The prostaglandins are members of an even larger
family of compounds called eicosanoids, all of
which contain 20 carbons and are derived from
polyunsaturated fatty acids
• thromboxanes
9
8
1
COOH
O
11
O
12
15
20
OH
Th romboxane A2
(a potent vasocons trictor)
Chemistry 121 Winter 2011 LA Tech
19-48
Eicosanoids
Leukotrienes
• found primarily in white blood cells
• one function is constriction of smooth muscles,
especially those of the lungs
OH
11
9
1
7
20
COOH
6 5
S
COOH
O
glycine
14
L-cysteine
Leu kotrien e C4 (LTC4)
(a smooth mus cle con strictor)
Chemistry 121 Winter 2011 LA Tech
N
H
HN
COOH
NH2
L-glutamic acid
O
19-49
Eicosanoids
Prostacyclin
1
5
HOOC
6
O
H
7
9 8
H
14
15
11
20
13
OH
OH
Pros tacyclin
(a platelet aggregation inh ibitor)
Chemistry 121 Winter 2011 LA Tech
19-50
Steroids
A group of plant and animal lipids that have this
tetracyclic ring structure
Chemistry 121 Winter 2011 LA Tech
19-51
Steroids
Fats similar to, and usually synthesized from,
cholesterol.
Chemistry 121 Winter 2011 LA Tech
19-52
Chemistry 121 Winter 2011 LA Tech
19-53
Steroids
Features common to steroids
CH3
H
CH3
C
A
H
D
B
H
H
• the fusion of rings is trans and each atom or group at a
ring junction is axial
• the pattern of atoms or groups along the ring junctions
is nearly always trans-anti-trans-anti-trans
• the steroid system is nearly flat and quite rigid
• most have axial methyl groups at C-10 and C-13
Chemistry 121 Winter 2011 LA Tech
19-54
Steroids
Cholesterol
H
H3 C
H3 C
*
HO
*
*
*
*
*
*
*
Ch oles terol has 8 s tereocen ters ;
256 stereois omers are possible
Chemistry 121 Winter 2011 LA Tech
H3 C
H
H
H
H
HO
H
This is the stereoisomer foun d in
h uman metab olis m
19-55
Steroids
Androgens - male sex hormones
• synthesized in the testes
• responsible for the development of male secondary sex
characteristics
H3 C
H3 C
OH
H
H
H
O
H3 C
H3 C
H
O
H
H
H
HO
Tes tos terone
Chemistry 121 Winter 2011 LA Tech
Androsterone
19-56
Steroids
Anabolic steroid: a steroid hormone, such as
testosterone, that promotes tissue and muscle
growth and development
HO
H3 C
CH3
H3 C
H3 C
H
H
H
H
O
H3 C
H
H
Chemistry 121 Winter 2011 LA Tech
H
H
H
H
HO
O
Meth androstenolone
HO
CH3
H3 C
OH
N androlon e
Methand riol
19-57
Steroids
Estrogens: female sex hormones
• synthesized in the ovaries
• responsible for the development of female secondary
sex characteristics and control of the menstrual cycle
CH3
H3 C
H3 C
C=O
H
H3 C
H
H
O
O
H
H
H
H
HO
Progesterone
Chemistry 121 Winter 2011 LA Tech
Es trone
19-58
Synthetic Estrogens
Progesterone-like analogs are used in oral
contraceptives
"Nor" refers to the abs ence
of a methyl group here.
It is present in ethindrone
HO C CH
H3 C
H
H
H
O
Chemistry 121 Winter 2011 LA Tech
H
Norethindrone
19-59
Steroids
Glucocorticoid hormones
•
•
•
•
synthesized in the adrenal cortex
regulate metabolism of carbohydrates
decrease inflammation
involved in the reaction to stress
CH2 OH
H3 C
O
H3 C
C=O
OH
H
H
C=O
H3 C
OH
HO
H3 C
H
O
CH2 OH
H
H
H
O
Cortisone
Chemistry 121 Winter 2011 LA Tech
Cortisol
19-60
Steroids
Mineralocorticoid hormones
• synthesized in the adrenal cortex
• regulates blood pressure and volume by stimulating
the kidneys to absorb Na+, Cl-, and HCO3OH
O
H3 C
CH
CH2 OH
C= O
H
H
H
O
Aldos terone
Chemistry 121 Winter 2011 LA Tech
19-61
Steroids
Bile acids
• synthesized in the liver, stored in the gallbladder, and
secreted into the intestine
• emulsify dietary fats and aid in their absorption and
digestion
H3 C
H3 C
H
HO
COOH
H
H
OH
H
Cholic acid
Chemistry 121 Winter 2011 LA Tech
19-62
Steroid Biosynthesis
The building block from which all carbon atoms of
steroids are derived is the two-carbon acetyl
group of acetyl-CoA
Stage 1: synthesis of isopentenyl pyrophosphate from
three molecules of acetyl-CoA (Sect 16.5)
Stage 2: synthesis of cholesterol
Stage 3: conversion of cholesterol to other steroids
cholesterol
bile acids (e.g., ch olic acid)
sex hormones (e.g., testosteron e and es trone)
mineralocorticoid h ormon es (e.g., ald os terone)
glucocorticoid hormones (e.g., cortisone)
Chemistry 121 Winter 2011 LA Tech
19-63
Biosynthesis Choresterol
O
CH3 -C-S-CoA
Acetyl Coen zyme A
O HO CH3
-
O
OH
(R)-Mevalonate
3-
OP2 O6
Is op entenyl pyroph os phate
C10 terpen es
( C1 0 ) Geranyl pyrophosp hate
C15 an d C20 terpen es
( C1 5 ) Farn esyl pyrophosp hate
C30 terpen es
( C3 0 ) Sq ualene
Cholesterol
Chemistry 121 Winter 2011 LA Tech
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Fat-Soluble Vitamins
Vitamins are divided into two broad classes on the
basis of their solubility
• those that are fat soluble (and hence classified as
lipids
• those that are water soluble
The fat-soluble vitamins include A, D, E, and K
Chemistry 121 Winter 2011 LA Tech
19-65
Vitamin A (Retinol)
• occurs only in the animal world
• found in the plant world in the form of a provitamin in a
group of pigments called carotenes
cleavage h ere
-Caroten e
enzyme-catalyzed
cleavage in the liver
CH2 OH
2
Retin ol
(Vitamin A)
Chemistry 121 Winter 2011 LA Tech
19-66
Vitamin A
The best understood role of vitamin A is its
participation in the visual cycle in rod cells
• the active molecule is retinal (vitamin A aldehyde),
which forms an imine with an -NH2 group of the protein
opsin to form the visual pigment called rhodopsin
• the primary chemical event of vision in rod cells is
absorption of light by rhodopsin followed by
isomerization of the 11-cis double bond to the 11-trans
configuration
Chemistry 121 Winter 2011 LA Tech
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Vitamin A
• isomerization of the double bond at C11-C12 is
triggered by light striking rhodopsin
11-12 cis configu ration
11
12
CH= N-opsin
light
11
CH= N-opsin
12
Chemistry 121 Winter 2011 LA Tech
19-68
Vitamin A
• a group of structurally related compounds that play a
role in the regulation of calcium and phosphorus
metabolism
• the most abundant form is vitamin D3
UV ligh t
HO
7-D ehydrocholesterol
HO
Vitamin D 3
Chemistry 121 Winter 2011 LA Tech
19-69
Vitamin E
Vitamin E: a group of compounds of similar
structure
• the most active is -tocopherol
• vitamin E functions as an antioxidant; it traps peroxy
radicals of the type HOO• and ROO• formed as a result
of oxidation by O2 of unsaturated hydrocarbon chains
in membrane phospholipids
OH
V itamin E
(-Tocoph erol)
O
Chemistry 121 Winter 2011 LA Tech
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Vitamin K
• the name of this vitamin comes from the German word
Koagulation, signifying its important role in the bloodclotting process
O
isoprene u nits
2
O
O
Vitamin K1
O
Menadione
(a synthetic vitamin K analog)
Chemistry 121 Winter 2011 LA Tech
19-71
Nonglyceride Lipids
Sphingolipids
steroids,
waxes
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Sphingolipids: Sphingosine
These lipids are based on sphingosine, are found in
plants and animals, and are common in the nervous
system.
Chemistry 121 Winter 2011 LA Tech
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Sphingolipids
CH CH CH2 12 CH3
CH CH CH2 12 CH3
CH OH
CH OH
O
CH NH C R1
CH2OH
ceramide
N-acylsphingosine
Chemistry 121 Winter 2011 LA Tech
O
CH NH C R1
O
+
CH2O P O CH2CH2N (CH3)3
O
sphingomyelin
A ceramide with
phosphocholine or
phosphoethanolamine as
head group
19-74
Sphingoglycolipids
Attachment of carbohydrates to primary -OH
of ceramide
Cerebrosides: contain a single moiety,
principally galactose
Sulfatides: sulfuric esters of
galactocerebrosides
Gangliosides: contain a complex
oligosaccharide moiety
Chemistry 121 Winter 2011 LA Tech
19-75
Sphingolipids
Chemistry 121 Winter 2011 LA Tech
19-76
Sphingoglycolipids-2
CH2 CH CH CH CH CH2
O NH OH
CH2OH
CO
O
H
H
R1
OH H
HO
H
H OH
a cerebroside
These compounds are found in the cell
membranes
of nerve and brain cells.
Chemistry 121 Winter
2011 LA Tech
CH
3
12
19-77
Clinical significance of
sphingolipids
Blood groups determined by various glycolipids on RBCs
Type 0
R
GlcNAc
Fucose
R
Type A
Galactose
Sialic acid (NANA)
R
Type B
Chemistry 121 Winter 2011 LA Tech
19-78
Estrogens
They are primarily responsible for the conversion of
girls into sexually-mature women. Participate in
the monthly preparation of the body for a
possible pregnancy. Participate in pregnancy if it
occurs
Chemistry 121 Winter 2011 LA Tech
19-79
Anabolic steroids
A number of synthetic androgens promote
an increase in body weight and muscle
strength: popular with athletes, weight
lifters, cyclists, professional football
players, etc.
Often these athletes take doses 100 time
greater than those used in standard
therapy. Such illicit use
Side effects: acne, a decrease in libido,
testicle size, and sperm counts to name a
few.
Chemistry 121 Winter 2011 LA Tech
19-80
Complex lipids
Lipoproteins
Lipoproteins are composed of a neutral core of
cholesterol and triacylglycerols.
Glycolipids
Sugar containing lipids
Chemistry 121 Winter 2011 LA Tech
19-81
Four major groups of plasma lipoproteins.
1. Chylomicrons
2. Very low-density lipoproteins (VLDL)
3. Low-density lipoproteins (LDL)
4. High-density lipoproteins (HDL)
Chemistry 121 Winter 2011 LA Tech
19-82
The roles of HDL, LDL, and cholesterol.
Cholesterol and lipoproteins are related plaque that
causes heart attacks and most strokes.
When LDL levels are low, atherosclerosis and heart
attacks are almost unknown.
High HDL levels are associated with a reduced risk
of heart disease: "good" cholesterol
Chemistry 121 Winter 2011 LA Tech
19-83
Sphingolipids
These lipids are based on sphingosine, are found in
plants and animals, and are common in the nervous
system.
CH CH CH2 12 CH3
CH OH
CH NH2
CH2OH
sphingosine
Chemistry 121 Winter 2011 LA Tech
19-84
Sphingolipids
CH CH CH2 12 CH3
CH CH CH2 12 CH3
CH OH
CH OH
O
CH NH C R1
CH2OH
ceramide
N-acylsphingosine
Chemistry 121 Winter 2011 LA Tech
O
CH NH C R1
O
+
CH2O P O CH2CH2N (CH3)3
O
sphingomyelin
A ceramide with
phosphocholine or
phosphoethanolamine as
head group
19-85
Sphingoglycolipids
Attachment of carbohydrates to primary -OH
of ceramide
Cerebrosides: contain a single moiety,
principally galactose
Sulfatides: sulfuric esters of
galactocerebrosides
Gangliosides: contain a complex
oligosaccharide moiety
Chemistry 121 Winter 2011 LA Tech
19-86
Sphingoglycolipids-2
CH2 CH CH CH CH CH2
O NH OH
CH2OH
CO
O
H
H
R1
OH H
HO
H
H OH
12
CH3
a cerebroside
These compounds are found in the cell
membranes
of nerve and brain cells.
Chemistry 121 Winter
2011 LA Tech
19-87
Clinical significance of sphingolipids
Blood groups determined by various glycolipids on RBCs
Type 0
R
GlcNAc
Fucose
R
Type A
Galactose
Sialic acid (NANA)
R
Type B
Chemistry 121 Winter 2011 LA Tech
19-88