midterm notes for chem31
TRANSCRIPT
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Lipids are a class of biological molecules defined
solubility in water and high solubility in nonpolar solven
Fatty acid is composed of a long hydrocarbon chain
and a terminal carboxyl group (or head). Natures
even number of carbon atoms (usually 14 to 24).
marine organisms, however, contain substantial am
fatty acids with odd numbers of carbon atoms.
Saturated FA (all carboncarbon bonds are single b
unsaturated FA (with one or more double bondshydrocarbon chain) mono unsaturated- has a single
bond, polyunsaturated- more than one. Stearic ac
and palmitic acid (16:0) are the most common satura
acids in nature. Oleic acid (18:1) (9) the most
unsaturated fatty acids
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FIGURE 8.1 the structures of some typical fatty aci
that most natural fatty acids contain an even number o
atoms and that the double bonds are nearly always
rarely conjugated.
This causes a bend or kink in the fatty acid chain. T
has very important consequences for the structure of b
membranes. Saturated fatty acid chains can pack
together to form ordered, rigid arrays under certain co
but unsaturated fatty acids prevent such close pac
produce flexible, fluid aggregates.
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These essential fatty acids include linoleic and -l
acids. These must be obtained by mammals in t
(specifically from plant sources).
Triacylglycerols /triglycerides)TAGS - are a majoreserve and the principal neutral derivatives of glycerol
animals. Are found primarily in the adipose tissu
fat) ,which serves as a depot or storage site fo
Monoacylglycerols and diacylglycerols also exist, bu
less common than the triacylglycerols. Most natural p
animal fat is composed of mixtures of simple and
triacylglycerols.
Acylglycerols can be hydrolyzed by heating with acid o
by treatment with lipases. Hydrolysis with alkali
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saponification and yields salts of free fatty acids and
(soap).
Simple TAGS all 3FA are the same
Mixed TAGS 2 or 3 different FA
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Fatty acids found in waxes are usually saturated.
The alcohols found in waxes may be saturated or uns
and may include sterols, such as cholesterol .Waxes i
insoluble due to the weakly polar nature of the ester g
a result, this class of molecules confers water-
character to animal skin, to the leaves of certain plant
bird feathers.
Triacontenolpalmitate major component of beeswa
Carnauba wax, obtained from the fronds of a speciestree in Brazil, is a particularly hard wax used for hi
finishes, such as in automobile wax, boat wax, floor w
shoe polish. Lanolin, a component of wool wax, is u
base for pharmaceutical and cosmetic products beca
rapidly assimilated by human skin.
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The terpenes are a class of lipids formed from combin
two or more molecules of 2-methyl-1,3-butadiene, bette
as isoprene (a five-carbon unit that is abbreviated C5).
monoterpene (C10) consists of two isoprene units.
sesquiterpene (C15) consists of three isoprene units.
diterpene (C20)has four isoprene units, and so on.
units can be linked in terpenes to form straight chain
molecules.
triterpenes are (C30) terpenes and include squalelanosterol, two of the precursors of cholesterol a
steroids.
Tetraterpenes (C40) are less common but incl
carotenoids, a class of colorful photosynthetic pigm
Carotene is the precursor of vitamin A, while lycopene
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to -carotene but lacking the cyclopentene rings, is a
found in tomatoes.
Long-chain polyisoprenoid molecules with a termina
moiety are called polyprenols. The dolichols, one
polyprenols (Figure 8.18), consist of 16 to 22 isopre
and, in the form of dolichyl phosphates, function
carbohydrate units in the biosynthesis of glycopro
animals. Polyprenyl groups serve to anchor certain pr
biological membranes.
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FIGURE 8.17 many monoterpenes are readily recog
their characteristic flavors or odors (limonene in
citronellal in roses, geraniums, and some perfumes; p
turpentine; and menthol from peppermint, used in cou
and nasal inhalers).
The diterpenes, which are (C20) terpenes, include ret
essential light-absorbing pigment in rhodops
photoreceptor protein of the eye), phytol (a const
chlorophyll), and the gibberellins (potent plant hormon
triterpene lanosterol is a constituent of wool fat. Lycop
carotenoid found in ripe fruit, especially tomatoes.
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A large and important class of terpene-based lipid
steroids. This molecular family, whose members e
amazing array of cellular functions, is based on a structural motif of three six-membered rings and o
membered ring all fused together.
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The structure of cholesterol, sho
steroid ring desi
and carbon numbering.
Cholesterol is the most common steroid in animals,
component of animal cell plasma membranes, comp
lipoprotein complexes in the blood; it is one of the con
of plaques that form on arterial walls in atheroscleros
steroids contain methyl groups at positions 10 and 13 a
to 10-carbon alkyl side chain at position 17. Many
contain oxygen at C-3, either a hydroxyl group in ste
carbonyl group in other steroids.
Steroid Hormones
Steroids derived from cholesterol in animals incl
families of hormones (the androgens, estrogens, pr
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glucocorticoids and mineralocorticoids) and bile acids
8.20). Androgens such as testosterone and estroge
as estradiol mediate the development of sexual chara
and sexual function in animals. The progestins
progesterone participate in control of the menstrual c
pregnancy. Glucocorticoids (cortisol, for e
participate in the control of carbohydrate, protein, a
metabolism, whereas the mineralocorticoids regu
(Na+, K+, and Cl-) balances in tissues. The bil
(including cholic and deoxycholic acid) are d
molecules secreted in bile from the gallbladder that ass
absorption of dietary lipids in the intestine.
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