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)

-Approximately what percentage of the population measured in Table 2 expresses GalNAcyl transferase?

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)

-Approximately what percentage of the population measured in Table 2 expresses GalNAcyl transferase?

Quizplus · Accepted Answer

11ecba2d_0ece_efd9_a3bf_ed24657f233a_MD0008_00 According to the passage, GalNAcyl transferase modifies the H-antigen by adding GalNAc in an α-1,3 glycosidic linkage to D-galactose, producing the A-antigen. Therefore, individuals who express the A-antigen on their red blood cells must express at least one copy of GalNAcyl transferase. This includes participants in the study with type A blood and those with type AB blood. Table 2 shows that 2746 participants had type A blood and 174 had type AB blood, for a total of 2920 participants who expressed the A-antigen. Therefore, 2920 participants expressed GalNAcyl transferase. The total number of participants was 10,000, so approximately 29% of the participants in the study expressed GalNAcyl transferase. (Choice B) Approximately 27% of participants had type A blood (2746/10,000), but individuals with type AB blood also express GalNAcyl transferase and must be counted in the calculation. (Choice C) Those with type B blood do not express GalNAcyl transferase. Approximately 11% of the participants had either type B blood or type AB blood (887+174/10,000). This represents the percentage of individuals who express galactosyl transferase. (Choice D) Approximately 9% of participants had type B blood (887/10,000). These individuals express galactosyl transferase, not GalNAcyl transferase. Educational objective: To determine the percentage of a population that meet specific criteria, all individuals with the relevant trait must be considered out of the total population evaluated.

Passage The ABO Blood Groups Are Determined by the Polysaccharide Antigens