Exam 3 Biochem-Lecture 30

Which are a component of all membranes but are particularly abundant in the myelin sheath???
Sphingolipids

 

Sphingomyelins are……that are also …….

  •  sphingolipids
  • phospholipids.

 

What are important structural lipid components of nerve cell membranes???

Sphingomyelins

 

The predominant sphingomyelins contain

palmitic or stearic acid N-acylated at carbon 2 of sphingosine.
The sphingolipids, like the phospholipids, are composed of

  • a polar head group
  • two nonpolar tails.

 The core of sphingolipids is
 the long-chain amino alcohol, sphingosine
Amino acylation, with a long chain fatty acid, at carbon 2 of sphingosine yields …..
a ceramide.

 

Sphingolipids include

  • the sphingomyelins 
  •  glycosphingolipids (the cerebrosides, sulfatides, globosides and gangliosides).

 Sphingomyelins are ……that are also ……

sphingolipids

phospholipids

 

The sphingomyelins are synthesized by the transfer of phosphorylcholine  from phosphatidylcholine to a ceramide in a reaction catalyzed by what enzyme? 

 sphingomyelin synthase

 

Sphingomyelin is degraded by………. a lysosomal enzyme that hydrolytically removes phosphorylcholine, leaving a ceramide. 

 sphingomyelinase

 

Defects in the enzyme acid sphingomyelinase result in the lysosomal storage disease known as :

Niemann-Pick disease.

 

There are at least how many related disorder identified as Niemann-Pick disease???

4 related disorders

 

4 related disorders identified as Niemann-Pick

disease are

Type A

Type B

Type C

Type D

 

Type A and B of Niemann-Pick disease

result from

defects in acid sphingomyelinase

 

Type C1, C2 and D of Niemann-Pick disease

do not result from defects in acid sphingomyelinase
Glycosphingolipids, or glycolipids are composed of
 a ceramide backbone with a wide variety of carbohydrate groups (mono- or oligosaccharides) attached to carbon 1 of sphingosine.
The four principal classes of glycosphingolipids are

  • cerebrosides
  • sulfatides
  • globosides
  • gangliosides

 

Cerebrosides have

a single sugar group linked to ceramide
The most common of Cerebrosides is

  • galactose (galactocerebrosides)
  • with a minor level of glucose(glucocerebrosides).

 

Galactocerebrosides are found

are found predominantly in neuronal cell membranes
Gluco-cerebrosides are

  • not normally found in membranes, especially neuronal membranes
  • They represent intermediates in the synthesis or degradation of more complex glycosphingolipids.

Galactocerebrosides are synthesized from
ceramide and UDP-galactose
Glucocerebrosides are synthesized from
ceramine and UDP-glucose

 

Fabry disease is characterized by

 

  • accumulation of globosides
  • a reddish-purple skin rash
  • kidney and heart failure
  • burning pain in the lower extremities.

 

Gaucher’s disease is characterized

by

  • accumulation of glucocerebroside
  • liver and spleen enlargement
  • erosion of long bones and pelvis
  • mental retardation in infantile form only.

 

NANA is

N-acetylneuraminic acid or sialic acid.

 

The linkage of NANA always involves ……..on the number ……… carbon of the carbohydrate.

the OH group

2

 

Gangliosides are very similar to globosides except that

     

 

 

they also contain NANA in varying amounts.

 

CNS is unique in that

more than 50% of the sialic acid is in gangliosides.