33. Metabolism of Sphingolipids: Sphingophospholipids and Glycolipids. Sphingolipidoses

Covers sphingophospholipids, with sphingomyelin as the key example, and glycolipids such as cerebrosides, sulfatides and gangliosides. It goes through structure, synthesis and degradation of each class, then their functions in membranes, signalling and myelin. A table of sphingolipidoses follows, listing the enzyme deficiency, accumulated lipid and key features of Tay-Sachs, Gaucher, Niemann-Pick, Krabbe and metachromatic leukodystrophy.

Inside: 6 sections · 5 labelled pictures · 15 flashcards · 3 min

Topic 33 of 76 in the MU Pleven syllabus for Biochemistry (Medicine, Year 2). The free AceMed note covers it in 6 sections, about 367 words (3 min of reading), with 15 flashcards.

Metabolism of Sphingolipids

1. Overview

Sphingolipids are complex lipids containing sphingosine as the backbone instead of glycerol.
They are major components of cell membranes, especially abundant in the brain and nervous tissue.
Two main classes:
Sphingophospholipids (contain phosphate group)
Glycolipids (contain carbohydrate group)

Sphingophospholipids

2. Key Example: Sphingomyelin

Composed of sphingosine + fatty acid (ceramide) + phosphocholine.
Found in myelin sheath of axons → essential for nerve conduction.

3. Synthesis of Sphingomyelin

Starts from serine + palmitoyl-CoA forming sphingosine.
Sphingosine + fatty acyl-CoA → Ceramide.
Ceramide + phosphatidylcholine → Sphingomyelin.

4. Degradation

Enzyme: Sphingomyelinase breaks sphingomyelin → Ceramide + Phosphocholine.
Ceramidase converts ceramide → Sphingosine + Fatty acid.

Glycolipids (Glycosphingolipids)

5. Structure

Ceramide + one or more sugar residues.
Located mainly in outer layer of plasma membrane.
No phosphate group.

6. Types

Cerebrosides: Ceramide + one sugar (glucose or galactose).
Sulfatides: Cerebrosides + sulfate group (negatively charged).
Gangliosides: Ceramide + complex oligosaccharides + N-acetylneuraminic acid (NANA).

7. Functions

Important in cell-cell recognition, hormone reception, signal transduction, and nerve tissue insulation.

8. Degradation

Occurs in lysosomes stepwise by specific enzymes removing sugars one at a time.