Sugar containing lipids

The glycosphingolipids (GSLs) are sugar-containing lipids built on a backbone of ceramide they include galactosyl- and glucosylceramide (cerebrosides) and the gangliosides. Their structures are described in Chapter 14. They are mainly located in the plasma membranes of cells. 

Relatively little is known about the possible interrelationships of the metabolism of the complex sugar-containing lipids, the glycosphingolipids (GSLs) and the plasma lipoproteins. 

Figure 22.11. Cellulose is a structural and rather chemically inert component of terrestrial plants. Alginic acid is synthesized by marine algae and has medicinal properties. Some polysaccharides contain nitrogen in the form of amino sugars. The primary example of this is chitin, which composes the exoskeletons of Crustacea. An amino sugar contains an amine in place of a hydroxyl group. In other polysaccharides, sugars combine with lipids and proteins. These form glycoUpids and glycoproteins, respectively.

There are three cases of proteins containing nonprotein components in addition to those just mentioned metalloproteins, glycoproteins, and lipoproteins. More about glycoproteins and lipoproteins follows later in this book when we get around to sugars and lipids. 

Botanically speaking, citrus is a hesperidium, a berry with a leathery aromatic rind and a fleshy interior divided into sections. As shown by the cross section shown in Fig. 6.1, the exo carp or peel consists of an outer layer called the flavedo which contains oil glands and pigments and a white spongy inner layer called the albedo. The fleshy interior or endocarp of the fruit consists of wedge-shaped sections (segments) filled with multiple fluid-filled sacs or vesicles. These juice sacs constitute the edible portion of a citrus fruit. The cytoplasm contents provide the primary source of the citrus juice. The juice consists primarily of water, sugars, pectins, lipids, terpenes, amino acids, phenolics, carotenoids and minerals. 

Proteins may consist exclusively of a polymeric chain of amino acids these are the simple proteins. Quite often some other chemical component is covalendy bonded to the amino acid chain. Glycoproteins and lipoproteins contain sugar and lipid components, respectively. Porphyrins are frequently associated with proteins, eg, in hemoglobin. Proteins bound to other chemical components are called conjugated proteins. Most enzymes are conjugated proteins. 

Morphine is extracted from the dried latex (opium) from the seed capsule of the poppy. Incisions, abont 1 mm deep, are made in the seed capsnle approximately two weeks after the petals have fallen from the flower and the seed head is mature, and the latex exndes from the seed head, dries and oxidizes in the sun and is collected the following day. With successive harvestings, a pod may produce anywhere between 10 and 100 mg of opium. The latex contains 10-20 wt% alkaloids, with the remainder of the latex being sugars, proteins, lipids, gums and water. 

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