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LIPIDS
They constitute he most abundant fraction of lipids and are present both in plants and in animals as energy storage.
Fats, oils, waxes
Esters of fatty acid
“fatty acids" are carboxylic acids of long unbranched chain, with evennumber of C atoms, saturated or unsaturated, with a number of C atomsusually from 12 to 20.
A lipid is defined as a naturally occurring organic compound that is insoluble inwater, but soluble in nonpolar organic solvents. Therefore, they include many typesof compounds.
Lipids: structurally different compounds, related to each other by a shared physical property, that is solubility in nonpolar or scarcely polar solvents (Hydrocarbons, chloroform, diethyl ether)
Fats and oils are triglycerides or triacylglycerols, both terms meaning “triesters of glycerol (1,2,3-propanetriol).
Waxes: simple ester of fatty acids with long chained alcohols.
CH3(CH2)14CO2(CH2)29CH3O
O
Example:
triacontyl hexadecanoate (bee wax)
CH2CHCH2
OHOHOH
CH2CHCH2
OO
ORO
R'O
R"O
glycerol1,2,3-propanetriol
R, R', R" may be equal or different, saturated or unsaturated
R CO
from 12 to 20 C
Saturated fatty acids are solid at room temperature (grease), because zig-zaghydrocarbon chains can fit compactly together, resulting in high van derWaals attractions.
Searic acid (octadecanoic acid)
CH2CH3CH2CH2 CCH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2 OH
O
Example:
O
OH
linolenic acid (9,12,15-ottadecatrienoic acid)
CH H
CH2CH3C C
CH2C
H H
CH2C
CH2 CCH2CH2CH2CH2CH2CH2
C
OH
OH H
191215
The presence of cis double bonds prevents the formation of neat, compactlattices and chains tend to coil and liquid at room temperature (oil)
Example:
O
OH912
15
CH2CHCH2
OHOHOH
CH2CHCH2
OO
OC
C
CRO R'
O
R"O
O C R"O
-
CROO-
C R'O
O-
glycerol
NaOH
Na+
+Na+
Na+H2O
Basic hydrolysis give glycerol and carboxylates of fatty acids (soaps)
In an organism, ingested fats are hydrolyzed into mono- and diglycerids, fatty acids, and glycerol, all absorbed hrough the intesinal wall.
CH2 OCORCH OCORCH2OCOR
CH2 OHCH OCORCH2OCOR
CH2 OHCH OHCH2 OCOR
CH2 OHCH OHCH2OH
H2Oenzymes + + + RCO2H
diglyceride monoglyceride glycerol fatty acid
Soaps are characterized by a polar head (carboxylate anion) and long nonpolar chains.
CO2-
Soaps in water do not dissolve, but aggregate giving micelles, clusters of hydrocarbonchains with their ionic heads facing the water. They do not dissolve, but the solutionlooks homogeneous.
grease
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2OH2O
H2O
H2OH2O
The soap micelles emulsify oily dirt, including it in the nonpolar core of micelle.
Detergents (synthetic solfonates) work in the same way
SO3- Na
+
Phospholipids
Phospholipids are lipids that contain phpsphate ester groups. They are of different types.Phosphoglycerids: they are closely related to the fats and oils. Thesecompounds usually contain fatty-acid esters at two positions ofglycerol with a phpsphate ester a the third position
R' contains a positive charge
such as, for exsmple:
CH2CH2 N(CH3)3O+
choline
They can be found almost exclusively in cell membranes
OO CO
CH2 N(CH3)3
CH2
CH
CH2O
O PO O
O CH2C
-+
polar head nonpolar tails
CH2CHCH2
OO
ORO
RO
PO
OHO R'
phosphatidylcholine (a lecitin)
Fosfatidiletanolammina (una cefalina)
C R
CH2 N(CH3)3O P O
OO
CH2
CH2
COCO
O
OCH2
HR+
-L
C R
CH2 NH3O P O
OO
CH2
CH2
COCO
O
OCH2
HR+
-
Lecithins and cephalins are two types of phpsphoglyceride hat are found in the brain, nerve cells, and liver of animals and are aldo found in food (egg yolks, wheat germ, yeast, soybeans, etc.)
phosphatidylethanolamine (a cholin)
CHCH2
OHN
OR'
HH
R"R',R" = HR' = COR, R" = H
R'= COR, R"= glycoside glycosphingolipidsceramidessphingosine
CHCH2
OHN
O PO
OO
H
OR"
N(CH3)3+
-sphingomyelin
Component of membranes and of myelinic coating of nervous cells
Sphingolipids
Example:
Sphyngomyekin is a phosphate ester of a long-chain allyl alcohol with an amide side chain.
Terpenes
All terpenes contain a number of C atoms multiple of 5. Sequences of 4 Cs + 1C in the side chain are repeated
The 5 carbon atoms structure is said “isoprene unit”: the end closer o the methyl branch is called “head”, the other end is indicated as “tail”.
headtail
The name “isoprene unit” derives from isoprene (methylbutadiene); acually, the unit involved in the biogenetic process is isopentenyl pyrophosphate
OO PO
OOP
O
O isoprenemethylbutadiene
-- -
isopentenyl pyrophosphateSimplest terpenes contain two isoprene units.
The odorous components of plants that can be separated from other plant materials by steam distillation are called essenial oils. Many essential oils are used in perfumes. Most essential oils are mixtures of terpenes, a class of natural products found in both plants and animals.
GLOSSARYó Terpenes with TWO isoprene units (C10) are monoterpenes.ó Terpenes with THREE isoprene units (C15) are sesquiterpenes.
ó Terpenes with SIX isoprene units (C30) are triterpenes.
ó Terpenes with FOUR isoprene units (C20) are diterpenes.
ó Terpenes with EIGHT isoprene units (C40) are tetraterpenes.
Generally, terpenes are constructed by the head-to-tail joining of isoprene units. However, head-to-head and tail-to-tail are also present.
tail
myrcenehead
tail
head a-pinene
limonene
(lemon)
10 C: two isoprene units monoterpene
zingiberene(ginger)
15 C: three isoprene units sesquiterpene
examples
myrcene(laurel)
10 C: two isoprene units monoterpene (head-to-tail)
a-pinene(conifers)
10 C: two isoprene units monoterpene
b-Carotene
tail-to-tail junction C 40: tetraterpene
H2OC H
OH
CO2HCO2H CH2
O H
OHCO2H CH2
OOH
Gibberelline A13
20 C: diterpene (considered a terpene, even if with only 18 C)growth hormone in plants
gibberellic acid
OH
squalene
biosynthesis
cholesterol
C 30: triterpene
biosynthesized by dimerization of two sesquiterpene (C 15) units
a steroid
C 40: tetraterpene
phytoene
SteroidsPolycycles with the structure of cyclopentanoperhydrophenanthrene
A B
C D1
2
34 5
67
8910
1112 13
14 15
16
17
Often methyl groups are present in 10 (number 19)and in 13 (number 18), called angular methylgroups; a C chain may be present in 17 (numbersfrom 20 on)
Tridimensional structure of steroids depends on the type of ring junction
Junctions between B and C rings and between C and D rings are ALWAYS transJunction between A and B rings may be either trans or cis
A B
bicyclo[4.4.0]decane (decalin)
Reference compound:
A and B rings are numbered first, then C ring and finally D ring are numbered, followed by side chains, if any
H
HHH
H
HH
H
H
H HH
H
H
HH
H
H
HHH
H
H
H
H
H
H
H HH
H
H
HH
H
H
2.5 Å
trans-decalineall chair boat-chair
H
H
H
H
H
H
H
H
HHH
H
HH
HH
H
H
2.17 Å
cis-decaline
Tridimensional structure of steroids:
CH3CH3 R
H
CH3CH3 R
H
5-a
b face
a face5-b
Steroids with trans A-B junction are called “5-a”, those with cis junction are indicated with “5-b”.
Systematic names of steroids are based on the saturated tetracyclic alkane with the same skeleton of C atoms
Nomenclature of steroids
C1-C27 CHOLESTANEC1-C24 CHOLANEC1-C21 PREGNANEC1-C19 ANDROSTANEC1-C18 ESTRANE
12
34 5 6
78910
1112
1314 15
1617
18
1920
2122
2324
2526
27
Deviations from thes base-skeletons is indicated with a prefix
Substituents and double bonds are indicated with respective prefixes and suffixes,together the number of thiddlee position they occupy and eventually the indication aor b (if they are below or above, respectively, the middle plane of the steroid).
Examples:
O
O
O
OH
Nandrolonesemisystematic:19-nortesterone (nor = missing)systematic: 17b-hydroxy-4-estren-3-one
progesteronC 21: 4-pregnen-3,20-dione
O Cholesterol5-cholesten-3b-ol
Cholesterol is the only steroidabundant in vertebrated, but has nohormonal activity
OH
CO2HCH3
CH3
H
OH
CO2H
lithocolic acid3a-hydroxy-5b-cholan-24-oic acid
OH ergosterol
sterol of yeast, gives Vitamin D2when irradiated
O
O
O
OHOH
cortisone
Hormone of adrenal cortex, used for treatment of arthritis
ProstaglandinsThey are carboxylic acids with 20 Cs and a ring. Together with tromboxanes and leucotrienes, thei costituite the group of eicosanoidd (from eicosanoic)acid
CO2H1
2
3
4
5
6
789
10
11 1213
14
15
16
17
1820
19
Prostaglandins are involved in stimulation or inhibition of smooth muscle;in regulatione of gastric secretion; in regulation of blood pressure; inregulation of muscle of respiration; intervene in inflammatory, nervous, andreproduttive processes.
Nomenclatura use semisysthematic names
Nomenclature delle prostaglandins
1. Three capital letters are used; the first two are PG (for prostaglandin), the third indicates how the cyclopentane ring is substituted.
Prostanoic acid
R'
C5H11HOO
O
O
PGG
R'
R"
O
O
PGH
O
R"OH
CH2CH2CH2CO2H
PGI
I tromboxanes are indicated with lettersTX leucotrienesi with letters LT O
R'
R"O
TXAOH
OHR'
R"TXB
OR'
R"
OR'
R"
OR'
R"
OR'
R"OH
OHR'
R"OH
OHR'
R"OPGA PGB PGC PGD PGE PGF
more important
2.C9 configuration is indicated with subscript a (below the plane or b (above the plane)
CO2H CO2H
O O
a chain 1
2
3
4
56
7R'= or135
6
7
4 2
w chain R"= 1314 15 16
17
18
19
20or 13
14 15 16
17 18
19
20
Side chain linked to C8 is called a chain; Side chain linked to C 12 is calledw chain; double bonds may be present in side chains: their number isindicated with a subscript
3.
OH
OH
OH
CO2HCO2H
OH
O
OHProstaglandin E1 Prostaglandin F2a
OH
CO2H
O H
H
H
H
O
Trombossano A2
CO2H
OH
O
OH
prostaciclina
CO2HH S
H OH
NH
OCO2H
NH2Leucotriene D4