Page 3 of 3: biochemistry

shravani · Credits: 6427 My Scrapbook

Which of the following structures is common to all sphingolipids?

A. Carnitine

B. Ceramide

C. Diacylglycerol

D. Sphingomyelin

E. Squalene

shravani · Credits: 6427 My Scrapbook

Explanation:

The correct answer is B. Sphingolipids are a class of lipids that are structural components of membranes.
Ceramide is a component of sphingolipids. Ceramide is composed of sphingosine, a long-chain amino alcohol
with a saturated fatty acid linked to the amino group. Sphingolipids can be differentiated on the basis of the "X"
group that is esterified to the terminal hydroxyl group of ceramide.

Carnitine (choice A) is involved in the oxidation of fatty acids. Carnitine is important in transferring fatty acids
from the cytoplasm into the mitochondria (the carnitine shuttle).

Diacylglycerol (choice C) is the alcohol common to all phospholipids. The second alcohol (e.g., choline,
ethanolamine, serine) contributes the polar head that distinguishes the different classes of phospholipids. Like
sphingolipids, phospholipids are found in membranes
Sphingomyelin (choice D) is a sphingolipid with phosphocholine as its "X" group. It is a component of the myelin
sheath.

Squalene (choice E) is a 30-carbon intermediate in the synthesis of cholesterol.

shravani · Credits: 6427 My Scrapbook

A 47-year-old male patient presents with painful arthritis in the right big toe and uric acid renal stones. He has
been taking allopurinol for his condition. What biochemical defect would likely be found in this patient?

A. A defect in urea synthesis

B. An abnormality of the purine degradation pathway

C. An inability to synthesize non-essential amino acids

D. Defective topoisomerases

E. Increased levels of leukotrienes

shravani · Credits: 6427 My Scrapbook

disease mostly affects males, and is frequently treated with allopurinol, an inhibitor of xanthine oxidase.
Xanthine oxidase catalyzes the sequential oxidation of hypoxanthine to xanthine to uric acid.

A defect in urea synthesis (choice A) would result in the accumulation of ammonia.

Phenylketonuria is a disease in which tyrosine cannot be produced from phenylalanine (choice C). It is
characterized by a musty body odor and mental retardation.

Defective topoisomerases (choice D) would affect DNA unwinding, and therefore replication.

Leukotrienes (choice E) are potent constrictors of smooth muscle and would more likely lead to
bronchoconstriction.

tamya · Credits: 203 My Scrapbook

the case history seems to be indicating leesch neehan syndrome..due to HGPRT deff..so ans is purine metabolism

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