Classes of Phospholipids

Study Notes

Common Phosphoglycerides

Phosphatidylserine (PS) forms from phosphatidic acid (PA) and serine.
Phosphatidylethanolamine (PE, cephalin) results from PA and ethanolamine.
Phosphatidylcholine (PC, lecithin) is created by combining PA with choline.
Phosphatidylglycerol (PG) derives from PA and glycerol.
Phosphatidylinositol (PI) is formed from PA and inositol.

Specialized Phospholipids

Cardiolipin is found exclusively in the inner mitochondrial membrane, crucial for respiratory complexes.
Plasmalogen functions as an antioxidant, protecting membrane phospholipids and includes platelet-activating factor (PAF).

Sphingomyelins

Sphingomyelins have a sphingosine backbone instead of glycerol.
They form through the amide linkage of sphingosine and fatty acids to create ceramide.
Phosphorylcholine esterifies carbon 1 of ceramide to produce sphingomyelin, essential for myelin in nerves.

Choline as an Essential Nutrient

Dipalmitoylphosphatidylcholine (DPPC) is vital for lung surfactant.
Synthetic surfactants are used to treat respiratory distress syndrome (RDS), also known as hyaline membrane disease.

Unique Aspects of Phosphatidylinositol

PI typically contains stearic acid on carbon 1 and arachidonic acid on carbon 2 of glycerol.
Serves as a reservoir of arachidonic acid, providing substrates for prostaglandin synthesis.

Role of PI in Signal Transduction

In signal transduction, GDP is exchanged for GTP.
Cell stimulation by hormones and neurotransmitters activates phospholipase C to cleave PIP2.
Produces inositol 1,4,5-trisphosphate (IP3) which mobilizes intracellular calcium, as well as diacylglycerol for protein kinase C activation.

Phospholipid Degradation

Various phospholipases target glycerophospholipid phosphodiester bonds.
Phospholipase A1 removes fatty acid from position 1.
Phospholipase A2 removes fatty acid from position 2, liberating arachidonic acid for signaling pathways.
Phospholipase C acts in liver lysosomes, producing second messengers from PIP2.
Phospholipase D cleaves alcohol from phosphoglycerides, yielding phosphatidic acid.

Neutral Glycosphingolipids

Cerebrosides represent the simplest form, consisting of ceramide and a monosaccharide (galactose or glucose).

Sphingolipidoses

Defective enzymes in glycosphingolipid degradation lead to substrate lipid accumulation, harming cells.
Degradation occurs in lysosomes, with hydrolase deficiencies causing lipid build-up.
Most sphingolipidoses result in neurological impairment and are typically fatal early in life; except Fabry Disease, an X-linked condition.

Niemann-Pick Disease

Characterized by accumulation in brain, liver, and spleen, leading to various health issues.

Tay-Sachs Disease

Involves the accumulation of GM2 gangliosides due to hexosaminidase A deficiency, leading to severe neurological impairment.

Fabry Disease

An X-linked disorder caused by deficiency of alpha-galactosidase A, resulting in cardiovascular, renal, and cutaneous complications.

Description

This quiz covers the various classes of phospholipids, including common phosphoglycerides and specialized phospholipids. Learn about the composition and significance of key phospholipids like phosphatidylcholine and cardiolipin. Ideal for students studying cell biology or biochemistry.