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Membrane Lipid Biosynthesis

Membrane Lipid Biosynthesis. Medical Biochemistry Lecture #51. METABOLISM OF ACYLGLYCEROLS AND SPHINGOLIPIDS.

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Membrane Lipid Biosynthesis

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  1. Membrane Lipid Biosynthesis Medical Biochemistry Lecture #51

  2. METABOLISM OF ACYLGLYCEROLS AND SPHINGOLIPIDS • Triacylglycerols are the major energy-storing lipids, whereas phosphoglycerols, sphingomyelin, and glycosphingolipids are amphipathic and fulfillmany roles, ranging from structural functions in cell membranes to specialized functions, i.e., precursors for hormone second messengers, lung surfactant, and platelet-activating factor.

  3. Biosynthesis of Triacylglycerols and Phosphoglycerols   - They are formed by acylation of triose phosphates.

  4. Biosynthesis of Glycerol ether phospholipids: -This pathway is exclusively located in peroxisomes.

  5. Phospholipases allow degradation and remodeling of phosphoglycerols:

  6. All Sphingolipids are formed from Ceramide: Ceramide is synthesized in the endoplasmic reticulum.

  7. Glycosphingolipids are a combination of Ceramide with one or more sugar residues: • The simplest glycosphingolipids (cerebrosides) are galactosylceramide (GalCer) and glucosylceramide (GlcCer).  • GalCer is the major lipid of myelin, whereas GlcCer is the major glycosphingolipids of exteraneuronal tissues and a precursor for most of the more complex glycosphingolipids.

  8. UDPGlc = Uridine diphosphoglucose UDPGal = Uridine diphosphogalactose

  9. CLINICAL ASPECTS: • Deficiency of lung surfactant causes Respiratory Distress Syndrome. Lung surfactant is a secretion with marked surface-active properties and prevents the alveoli from collapsing.   • It is mainly composed of lipids, i.e., dipalmitoylphosphatidylcholine which is synthesized shortly before parturition in full-term infants. Preterm new-borns have this syndrome due to deficiency of lung surfactant.  • Administration of either natural or artificial surfactant has been useful. 

  10. Phospholipids Sphingolipids are involved in Multiple Sclerosis (M.S.) and Lipidoses • MS is a demyelinating disease, there is loss of both phospholipids and of sphingolipids from white matter. Thus, the lipid composition of white matter resembles that of gray matter. The cerebrospinal fluid shows raised phospholipid levels.  • Sphingolipidoses are a group of inherited diseases that are often manifested in childhood. These diseases are part of a larger group of lysosomal disorders.  • There is an accumulation of complex lipids that have a portion of their structure in common-Ceramide.   • The enzymatic defect in each of these diseases is a deficiency due to gene mutation of a specific lysosomal hydrolytic enzyme necessary to break down the lipid or of a key activator protein of the enzyme.

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