Glycolipids

Glycolipids

Q. 1 Glycerol  is  the  backbone  of  all  of  the following phospholipids EXCEPT
 A Phosphatidylethanolamine
 B Cardiolipin
 C Phosphatidylcholine
 D Sphingomyelin
Q. 1 Glycerol  is  the  backbone  of  all  of  the following phospholipids EXCEPT
 A Phosphatidylethanolamine
 B Cardiolipin
 C Phosphatidylcholine
 D Sphingomyelin
Ans. D

Explanation:

Sphingomyelin   = phosphorylcholine + ceramide

Ceramide            = fatty acid + sphingosine

Sphingosine        = condensing palmitic acid with a decarboxylated   serine   and   then   reducing   the product

Glycerol  never  is  involved  in  the  structure  of sphingomyelin. Phosphatidylethanolamine, cardiolipin, phosphatidylcholine, and phosphatidylinositol are synthesized using phosphatidic acid as the basic building block  Phosphatic acid  is  diacylglycerol with a phosphate  ester on carbon three; therefore, glycerol is the backbone of all of these compounds. FAQ Sphingomyelin :-

–  Membranous myelin sheath that surrounds nerve cell axons.

–    It is the only sphingolipid NOT derived from Glycerol.

–       Associated  with  increased  accumulation  in Niemann-Pick  Disease.


Q. 2

Which of the following occurs in the lipidosis known as Tay-Sachs disease?

 A

Synthesis of a specific ganglioside is excessive

 B

Xanthomas due to cholesterol deposition are observed

 C

Phosphoglycerides accumulate in the brain

 D

Ganglioside GM2 is not catabolized by lysosomal enzymes

Q. 2

Which of the following occurs in the lipidosis known as Tay-Sachs disease?

 A

Synthesis of a specific ganglioside is excessive

 B

Xanthomas due to cholesterol deposition are observed

 C

Phosphoglycerides accumulate in the brain

 D

Ganglioside GM2 is not catabolized by lysosomal enzymes

Ans. D

Explanation:

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 β-N- acetylhexosaminidase.

The elevated GM2 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.

The cause of most lipidoses (lipid storage diseases) is similar.

That is, a defect in catabolism of gangliosides causes abnormal accumulation.

None of the other choices result in lipidotic disorders. 

Ref: Hopkin R., Grabowski G.A. (2012). Chapter 361. Lysosomal Storage Diseases. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo (Eds), Harrison’s Principles of Internal Medicine, 18e.

 


Q. 3

Glycosphingolipidis made up of:

 A

Glucose

 B

Fatty acids

 C

Sphingosine

 D

All Correct

Q. 3

Glycosphingolipidis made up of:

 A

Glucose

 B

Fatty acids

 C

Sphingosine

 D

All Correct

Ans. D

Explanation:

A, B, C i.e. Glucose, Sphingosine, Fatty acids

Glycosphingolipid = Ceramide (Sphingosine / amino alcohol + Fatty acid) + Mono/oligo saccharide like glucose, galactose. Ganglioside (acidic glycosphingolipid) = Ceramide + Oligosaccharide + NANA (N-acetylneuraminic acid or sialic acid)

 

–  Glyco-sphingolipid is made up of ceramide (which is a long chain fatty acid attached to amino group of sphingosine through an amide linkage i.e. = sphingosine/ amino alcohol + Fatty acid) attached directly to mono /oligo saccharide

(polar head) by an 0-glycosidic bond. Glycosphingolipids differ from sphingomyelin (phospho- sphingolipid) in that they do not contain phosphate (polar group); and differ from glycerophospholipids (phosphoglycerides) that they do not contain glycerol.

Ganglioside (acidic, negatively charged glyco-sphingolipid) contain sphingosine alcohol (4 sphingenine) 1 molecule, long chan fatty acid (1 mol), Oligosaccharide polar head and 1 or more residues of N- acetylneurminic acid (Neu 5 Ac), a sialic acid (often simply called sialic acid) giving it a negative charge, at termini. Ganglioside do not contain glycerol and phosphateQ.

Ceramide containing sphingosine amino alcohol is present in all sphingolipids (ie. phospho & glyco- sphingolipids)Q.



Q. 4

Which of the following is not a glycerosphingolipid?

 A

Lecithin

 B

Cardiolipin

 C

Plasmalogens

 D

Sphingomyelin

Q. 4

Which of the following is not a glycerosphingolipid?

 A

Lecithin

 B

Cardiolipin

 C

Plasmalogens

 D

Sphingomyelin

Ans. D

Explanation:

 

Phospholipids are :

  1. Glycerophospholipids (glycerol containing) :- Phosphatidylcholine (lecithin), phosphatidylethanolamine (cephaline), phosphatidylserine, phosphatidylinositol, plasmalogens, lysophospholipids, cardiolipin.
  2. Sphingophospholipids (sphingosine containing) :- Sphingomyeline

Quiz In Between



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