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CASE FILES: BIOCHEMISTRY
[28.2] Tay-Sachs
disease
involves
the
metabolism
of
gangliosides.
Gangliosides are composed of a ceramide backbone with at least which
one of the following?
A. Phosphorylated sugar residue
B. Glucose residue
C. Galactose residue
D. Sialic acid residue
E. Fructose residue
[28.3] The genetic disease which results from a mutation in the gene coding
for the enzyme hexosaminidase (P-N-acetylhexosaminidase) is called
what?
A. Huntington disease
B. Lesch-Nyhan syndrome
C. Tay-Sachs disease
D. Amyotrophic lateral sclerosis
E. Neurofibromatosis
A nsw ers
[28.1]
A. Tay-Sachs disease is the result of the lack of the enzyme
fi-N-
acetylhexosaminidase. This enzyme hydrolyzes a terminal N-
acetylgalactosamine from the ganglioside GM2. This ganglioside is
found in high concentrations in the nervous system and is normally
degraded in the lysosome by the sequential removal of terminal sug-
ars. The lack of P-N-acetylhexosaminidase results in the accumula-
tion of the partially degraded ganglioside in the lysosome leading to
significant swelling of the lysosome. The abnormally high level of
lipid in the lysosome of the neuron affects its function resulting in the
disease.
[28.2]
D. Gangliosides are carbohydrate-rich lipids in which an oligosac-
charide chain is attached to ceramide. The oligosaccharide chain
must contain at least one acidic sugar such as
N
-acetylneuraminate or
N
-glycosylneuraminate. These sugars are commonly referred to as
sialic acid residues. Gangliosides are synthesized by the stepwise
addition of sugar residues to ceramide.
[28.3]
C. Tay-Sachs disease is the result of the lack of the enzyme P-N-
acetylhexosaminidase. Affected infants show weakness and retarded
motor skills before 1 year of age. Other abnormalities follow, and
death usually occurs before age 3.
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