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chapter 10

Heteropolysaccharides I: Glycoproteins and Glycolipids

(d)

Cholesterol

C h o lestero l (3-hydroxy-5,6-cholestene) b e lo n g s to a family of c o m p o u n d s derived from a fu sed , red u ced , n o n lin ear four-ring sy ste m of

cy clo p en taf a ]-p h e n a n th re n e. Bile a d d s , steroid h o rm o n es, a n d vitam in D m etabolites a re d eriv ed from cholesterol.

C onform ational

form ula

(e)

Glycosphingollplds (gangllosldes)

C eram id e o lig o sacch arid es consisting of a t le a st o n e resid u e of sialic a d d a re know n a s g an g lio sid es. T h e s e a re ab b rev iated by th e letter G

with a su b scrip t M (m ono), D (di), o r T (tri) to indicate th e n u m b er of sialyl re sid u es a n d a n u m b e r (or letter) to distinguish different m em b ers

of a g ro u p from e a c h other. G an g lio sid es a re particularly rich in n e rv o u s tissu e s. Following is th e stru ctu re of ganglioside G ut.

O H

I

8

G alactosyl-p - ( 1 -3 ) N -acetylgalactosam inyl- p -( 1 - 4 ) g alacto sy l-p -( 1 - 4 ) glucosyl ceram id e

Sialyl

F I G U R E 1 0 -5

(

Continued

)

components of the bilayers and their role in natural

membranes. Liposomes are formed when phospholipids

are shaken vigorously in an aqueous medium. Electron

microscopic studies of liposome vesicle reveal “sealed”

concentric bilayers with the aqueous phase trapped on the

inside (Figure 10-8). Known substances can be entrapped

in liposomes, and permeability properties can be studied

under experimental conditions. Liposomes have potential

applications in medicine. Drugs and macromolecules (e.g.,

enzymes and nucleic acids) encapsulated in liposome sys-

tems can be targeted to a particular cell population or organ

system.