Question 1

The parents of a 7-month-old infant bring their son to the pediatrician because they have noticed that their child has a dull response to outside stimuli. In addition, they note that their child exhibits an exaggerated startle response (sudden extension of arms and legs) to sharp sounds and that he seems to be losing previously acquired motor and mental skills. His pediatrician makes a diagnosis of Tay-Sachs disease. Elevated intracellular levels of which of the following carbohydrate-containing compounds would provide useful information for confirmation of this diagnosis?

A) abnormal glycogen
B) aldohexoses
C) aldoketoses
D) gangliosides
E) glycosaminoglycans

gangliosides

Accepted Answer

In the genetic disorder known as Tay-Sachs disease, ganglioside GM2 is not catabolized. As a consequence, the ganglioside concentration is elevated many times higher than normal. The functionally absent lysosomal enzyme is b-N-acetyl hexosaminidase (more commonly called hexosaminidase A). The elevated GM 2 results in irreversible brain damage to infants, who usually die before the age of 3 years. Under normal conditions, this enzyme cleaves N-acetylgalactosamine from the oligosaccharide chain of this complex sphingolipid, allowing further catabolism to occur. Tay-Sachs disease is characterized by the accumulation of gangliosides, specifically GM2 gangliosides, due to a deficiency in the enzyme hexosaminidase A.

Question 2

The parents of an 18-month-old girl are alarmed at the rapid deterioration in her motor skills and the appearance of an engorged belly. They note that when their daughter tries to follow the movement of an object she thrusts her head in the direction of movement as if she cannot move her eyes from side-to-side. Physical and laboratory examination reveals that the child is suffering from Gaucher disease. Which of the following carbohydratecontaining compounds would be expected to be elevated in macrophages from this patient?

A) abnormal glycogen
B) cerebrosides
C) glycosaminoglycans
D) MG² ganglioside
E) neuraminic acid

Accepted Answer

Gaucher disease is characterized by the accumulation of glucocerebrosides in macrophages due to a deficiency in the enzyme glucocerebrosidase.

Question 3

The aldehyde and ketone moieties of the carbohydrates with 5 and 6 carbons will spontaneously react with alcohol groups present in neighboring carbons to produce ring structures. The rings can open and close allowing for different configurations of the atoms in the ring. Which of the following represents the carbon about which this rotation occurs?

A) anomeric
B) chiral16 part i Biological Building Blocks of Cells and Tissues
C) glycosidic
D) hydroxy
E) terminal

anomeric

Accepted Answer

The carbon about which the rotation occurs in ring structures of carbohydrates is the anomeric carbon and the 2 forms are termed anomers The carbon about which the rotation occurs in carbohydrates is the anomeric carbon. This carbon is the one that was originally the carbonyl carbon (aldehyde or ketone) before the ring closure and is involved in forming the hemiacetal or hemiketal linkage.

Question 4

A deficiency in the hepatic enzyme aldolase B would result in a reduced ability to metabolize which of the following carbohydrates?&#10;A) dihydroxyacetone&#10;B) fructose&#10;C) glucose&#10;D) glyceraldehyde&#10;E) sucrose

Accepted Answer

Hepatic aldolase B is responsible for the hydrolysis of fructose-1-phosphate into dihydroxyacetone phosphate and glyceraldehyde. The fructose- 1-phosphate is derived via the action of ketohexokinase (fructokinase) and thus if aldolase B is deficient downstream utilization of fructose will be impaired. A deficiency in aldolase B impairs the metabolism of fructose, leading to an accumulation of fructose-1-phosphate in the liver.

Question 5

You are examining a patient complaining of cramping in the lower belly, bloating, gas, and diarrhea. These symptoms appear within 30 minutes to 2 hours after the ingestion of dairy products. You advise your patient to avoid foods that contain a particular sugar. Which of the following is the sugar this patient should avoid?

A) glucose
B) lactose
C) sucrose
D) fructose
E) galactose

Accepted Answer

The symptoms described are indicative of lactose intolerance, where the body is unable to properly digest lactose, a sugar found in dairy products.  The patient is most likely deficient in intestinal lactase and is thus, lactose intolerant. The signs and symptoms of lactose intolerance usually begin 30 minutes to 2 hours after eating or drinking foods that contain lactose and include nausea, vomiting, diarrhea, bloating, gas, and painful abdominal cramping.

Deck 2: Biological Building Blocks: Carbohydrates