Passage
Nerve cells must maintain the composition of their myelin sheaths to function properly. Galactocerebroside (GC) , shown in Figure 1, is a hydrolyzable lipid and an important component of the myelin sheath.
Figure 1 Structure of the myelin sheath component galactocerebrosideHomeostasis of GC is maintained by its dynamic synthesis and degradation, as shown in Figure 2. GC is synthesized by the enzyme ceramide galactosyltransferase (CGT) using UDP-galactose (UDP-Gal) and ceramide (Cer) as substrates. It is degraded by the enzyme galactocerebrosidase (GalC) , which hydrolyzes the glycosidic bond to release galactose (Gal) and ceramide. A deficiency in GalC activity leads to a buildup of GC, and prior research has connected this buildup with neurodegeneration.
Figure 2 Schematic of GCT and GalC activity in healthy and GalC deficient cellsOver 100 inactivating GalC mutations have been identified. Five of the most common mutations are listed in Table 1. The changes to both DNA and amino acid sequence are shown.Table 1 Five Common Galactocerebrosidase Mutations

-GC can be classified as:

Question

Passage
Nerve cells must maintain the composition of their myelin sheaths to function properly. Galactocerebroside (GC) , shown in Figure 1, is a hydrolyzable lipid and an important component of the myelin sheath.

Figure 1 Structure of the myelin sheath component galactocerebrosideHomeostasis of GC is maintained by its dynamic synthesis and degradation, as shown in Figure 2. GC is synthesized by the enzyme ceramide galactosyltransferase (CGT) using UDP-galactose (UDP-Gal) and ceramide (Cer) as substrates. It is degraded by the enzyme galactocerebrosidase (GalC) , which hydrolyzes the glycosidic bond to release galactose (Gal) and ceramide. A deficiency in GalC activity leads to a buildup of GC, and prior research has connected this buildup with neurodegeneration.

Figure 2 Schematic of GCT and GalC activity in healthy and GalC deficient cellsOver 100 inactivating GalC mutations have been identified. Five of the most common mutations are listed in Table 1. The changes to both DNA and amino acid sequence are shown.Table 1 Five Common Galactocerebrosidase Mutations

-GC can be classified as:

Quizplus · Accepted Answer

11ecba2d_0e66_425c_a3bf_31f73af1913f_MD0008_00 Lipids are a broad class of hydrophobic biomolecules that are categorized at multiple levels. At a general level, they are classified as hydrolyzable or nonhydrolyzable based on whether they contain hydrolyzable linkages such as esters or amides. Hydrolyzable lipids are further classified based on their backbone structure and modifications. For example, lipids built on a glycerol backbone are glycerolipids, whereas those built on sphingosine backbones are sphingolipids. A lipid with a phosphate group modification is called a phospholipid, and a lipid with a carbohydrate attached is called a glycolipid. Multiple characteristics may be present at once, yielding more complex names such as glycerophospholipids, phosophosphingolipids, glycosphingolipids, or phosphoglycolipids. The passage states that GC is a hydrolyzable lipid. The structure in Figure 1 shows that it is built on a sphingosine backbone, making it a sphingolipid. Figure 1 and the passage also show that GC includes the carbohydrate galactose, attached to the lipid by a glycosidic bond (glycosylation). Because GC is a sphingolipid that has been glycosylated, it can be classified as a glycosphingolipid. (Choice A) Glycerophospholipids contain a phosphate group and are built on a glycerol backbone. Neither is true of galactocerebroside, so it cannot be classified as a glycerophospholipid. (Choices B and D) Galactocerebroside does not contain a phosphate group, so it cannot be classified as a phosphosphingolipid or a phosphoglycolipid. Educational objective: Hydrolyzable lipids are classified according to their modifications. Those with sphingosine backbones are sphingolipids; those with glycerol backbones are glycerolipids; phosphate modifications yield phospholipids; and carbohydrate modifications yield glycolipids. Complex lipids may involve a combination of these characteristics and are named accordingly (ie, glycosphingolipid, glycerophospholipid).

Passage Nerve Cells Must Maintain the Composition of Their Myelin Sheaths