Biochemistry · MU Sofia

28. METABOLISM OF GLYCEROPHOSPHATIDES…

Covers glycerophosphatides (phospholipids): their degradation by phospholipases A1, A2, C and D and by lysophospholipase, and their synthesis from phosphatidic acid and diacylglycerol with head groups such as choline, ethanolamine and serine. It then describes sphingolipids, including ceramides, sphingomyelins and glycosphingolipids, and the lysosomal storage disorders Gaucher, Tay-Sachs and Niemann-Pick, with their enzyme deficiencies, symptoms and treatments. Four multiple-choice questions with answers close the note.

Inside: 17 sections · 11 labelled pictures · 10 flashcards · 7 min

Topic 28 of 70 in the MU Sofia syllabus for Biochemistry (Medicine, Year 2). The free AceMed note covers it in 17 sections, about 1,033 words (7 min of reading), with 10 flashcards.

In this note

  1. Introduction
  2. Phosphilipids
  3. Degradation
  4. Synthesis of phospholipids
  5. Synthesis:
  6. Phosphatidic Acid Synthesis
  7. Phospholipases A1, A2, C, and D
  8. Sphingolipids
  9. Sphingolipidoses
  10. Gaucher Disease:
  11. Gaucher Disease Symptoms:
  12. Tay-Sachs Disease:
  13. Tay – Sachs Disease Symptoms:
  14. Niemann-Pick Disease:
  15. Niemann-Pick Disease Symptoms:
  16. MCQs ☺
  17. Answers

Introduction

Glycerophosphatides, also known as phospholipids, are a class of lipids containing a glycerol backbone linked to two fatty acid chains and a phosphate-containing head group.

They are vital components of cell membranes and play roles in cell signalling and lipid metabolism.

Degradation

  • Phospholipase A2 (PLA2) Action: Cleaves the fatty acid at the sn-2 position, releasing a lysophospholipid and a free fatty acid.
  • Lysophospholipase Action: Further hydrolyzes the lysophospholipid to yield glycerol and a free fatty acid.

Synthesis of phospholipids

  • Phospholipids are synthesized from phosphatidic acid & 1,2-diacylglycerol, intermediates in the production of triacylglycerols.
  • Phospholipids synthesis occurs in the smooth endoplasmic reticulum.
  • Inner mitochondrial membrane

Synthesis:

  • Glycerol-3-Phosphate Backbone Formation: Glycerol-3-phosphate is acylated with two fatty acids to form phosphatidic acid (PA).
  • Head Group Addition: A head group (e.g., choline, ethanolamine, serine) is attached to the phosphate of PA, forming various phospholipids like phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylserine (PS).

Phospholipases A1, A2, C, and D

Phospholipases are enzymes that catalyze the hydrolysis of phospholipids, playing crucial roles in cell signalling, membrane remodelling, and lipid metabolism.

  • Phospholipase A1 (PLA1):
  • Cleaves the fatty acid at the sn-1 position of phospholipids, releasing a fatty acid and a lysophospholipid.
  • Phospholipase A2 (PLA2):
  • Hydrolyzes the fatty acid at the sn-2 position of phospholipids, yielding a lysophospholipid and a free fatty acid.
  • Phospholipase C (PLC):
  • Cleaves phospholipids at the phosphate group, generating diacylglycerol (DAG) and a phosphorylated head group.
  • Phospholipase D (PLD):
  • Catalyzes the hydrolysis of phospholipids to produce phosphatidic acid (PA) and a free head group (e.g., choline).

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