midterm notes for chem31

8/6/2019 Midterm Notes for Chem31

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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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midterm notes for chem31

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