MCAT Biochemistry Question 59: Answer and Explanation

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Question: 59

14. Andersen's disease (glycogen storage disease type IV) is a condition characterized by a deficiency in glycogen branching enzyme. Absence of this enzyme would be likely to cause all of the following effects EXCEPT:

  • A. decreased glycogen solubility in human cells.
  • B. slower action of glycogen phosphorylase.
  • C. less storage of glucose in the body.
  • D. glycogen devoid of α-1,4 linkages.

Correct Answer: D

Explanation:

In Andersen’s disease, glycogen is less branched than normal, thereby inducing lower solubility of glycogen. Branches reduce the interactions between adjacent chains of glycogen and encourage interactions with the aqueous environment. The smaller number of branches means that glycogen phosphorylase has fewer terminal glucose monomers on which to act, making enzyme activity slower than normal overall. Finally, without branches, the density of glucose monomers cannot be as high; therefore, the total glucose stored is lower than normal. Glycogen synthase is still functioning normally, so we would expect normal α-1,4 linkages in the glycogen of an individual with Andersen’s disease but few (if any) α-1,6 linkages.

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