Passage
The ABO blood groups are determined by the polysaccharide antigens linked to sphingolipids on red blood cell membranes. The polysaccharide known as the H-antigen (O-type blood) consists of a polysaccharide (R-group) glycosidically linked to D-galactose, which is connected to L-fucose in an α-1,2 linkage. Type A and type B blood express the A- and B-antigens, respectively (Figure 1) . These antigens are modified forms of the H-antigen, in which D-galactose (B-antigen) or a derivative of D-galactose called GalNAc (A-antigen) is added in an α-1,3 linkage to the D-galactose moiety of the H-antigen.
Figure 1 Structures of the H-, A-, and B-antigens. The R-group represents additional carbohydrates.The addition of GalNAc or galactose to the H-antigen is catalyzed by an enzyme encoded by the ABO gene. One allele of the gene encodes GalNAcyl transferase and produces the A-antigen, while another allele encodes galactosyl-transferase and yields the B-antigen (Figure 1) . The two alleles differ at seven nucleotide positions, summarized in Table 1.Table 1 Nucleotide Positions Where the Alleles Encoding GalNAcyl Transferase and Galactosyl Transferase Differ
Individuals with both alleles express both antigens and have type AB blood. Those with type O blood have a third allele that encodes an inactive form of the enzyme. A study of blood type abundance was conducted, and the number of participants with each type is shown in Table 2. Table 3 shows several fatty-acyl chains found in the sphingolipids to which the antigens were attached.Table 2 Number of Participants That Express Each Blood Type in a Study of 10,000 Individuals
Table 3 Types of Sphingolipids to Which Polysaccharide Antigens Were Bound, as Determined by Mass Spectrometry (Note: For fatty acid chains, the numbers on the left and right of the colon indicate number of carbons and number of C=C double bonds, respectively)

-Which of the following statements accurately describes the sphingolipids in Table 3?They provide structure to biological membranesThey are primarily used for energy storageThey can be hydrolyzed to produce two fatty acids

Question

Passage
The ABO blood groups are determined by the polysaccharide antigens linked to sphingolipids on red blood cell membranes. The polysaccharide known as the H-antigen (O-type blood) consists of a polysaccharide (R-group) glycosidically linked to D-galactose, which is connected to L-fucose in an α-1,2 linkage. Type A and type B blood express the A- and B-antigens, respectively (Figure 1) . These antigens are modified forms of the H-antigen, in which D-galactose (B-antigen) or a derivative of D-galactose called GalNAc (A-antigen) is added in an α-1,3 linkage to the D-galactose moiety of the H-antigen.

Figure 1 Structures of the H-, A-, and B-antigens. The R-group represents additional carbohydrates.The addition of GalNAc or galactose to the H-antigen is catalyzed by an enzyme encoded by the ABO gene. One allele of the gene encodes GalNAcyl transferase and produces the A-antigen, while another allele encodes galactosyl-transferase and yields the B-antigen (Figure 1) . The two alleles differ at seven nucleotide positions, summarized in Table 1.Table 1 Nucleotide Positions Where the Alleles Encoding GalNAcyl Transferase and Galactosyl Transferase Differ

Individuals with both alleles express both antigens and have type AB blood. Those with type O blood have a third allele that encodes an inactive form of the enzyme. A study of blood type abundance was conducted, and the number of participants with each type is shown in Table 2. Table 3 shows several fatty-acyl chains found in the sphingolipids to which the antigens were attached.Table 2 Number of Participants That Express Each Blood Type in a Study of 10,000 Individuals

Table 3 Types of Sphingolipids to Which Polysaccharide Antigens Were Bound, as Determined by Mass Spectrometry (Note: For fatty acid chains, the numbers on the left and right of the colon indicate number of carbons and number of C=C double bonds, respectively)

-Which of the following statements accurately describes the sphingolipids in Table 3?They provide structure to biological membranesThey are primarily used for energy storageThey can be hydrolyzed to produce two fatty acids

Quizplus · Accepted Answer

11ecba2d_0ece_0578_a3bf_c908eff35f8e_MD0008_00 Lipids are broadly classified as either hydrolyzable or nonhydrolyzable. They can also be grouped by function as structural lipids, energy-storing lipids, and signaling lipids. Structural lipids are found in the membranes surrounding cells and organelles and include hydrolyzable glycerophospholipids and sphingolipids as well as nonhydrolyzable cholesterol. The properties of individual lipids such as the number of fatty acid tails, double bonds, and head group structures influence both fluidity and curvature of biological membranes. The sphingolipids in Table 3 contain a sphingosine backbone attached to a single fatty acyl chain and a polar head group. In red blood cells and other cell types these sphingolipids are essential structural components of the plasma membrane (Number I). (Number II) The lipids that are primarily responsible for energy storage are triacylglycerides, which are metabolized through hydrolysis and beta-oxidation. The fatty acyl groups of sphingolipids may be hydrolyzed and used for energy production, but this is not their primary function. (Number III) Glycerophospholipids contain two hydrolyzable fatty acyl chains, but sphingolipids contain only one. The other long chain hydrocarbon in a sphingolipid is part of the sphingosine backbone and cannot be hydrolyzed. Therefore, sphingolipids produce one fatty acid upon hydrolysis, not two. Educational objective: Sphingolipids are structural lipids that help influence the fluidity and curvature of biological membranes. The long hydrocarbon chain of the sphingosine head group cannot be readily hydrolyzed, and sphingolipids are not a primary means of energy storage.

Passage The ABO Blood Groups Are Determined by the Polysaccharide Antigens