Phospholipids and Ether Lipids

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Questions and Answers

What type of phospholipid is abundant in nerve tissue?

Sphingomyelin

Phosphatidylethanolamine

Phosphatidylcholine

Phosphatidalethanolamine (correct)

What is the function of Platelet-activating factor (PAF)?

To activate inflammatory cells and mediate hypersensitivity reactions (correct)

To generate superoxide radicals to kill bacteria

To prevent thrombotic and acute inflammatory events

To lower blood pressure

What is the backbone of Sphingomyelin?

Phosphatidalcholine

Phosphatidylethanolamine

Sphingosine (correct)

Glycerol

What is the effect of Platelet-activating factor (PAF) on platelets?

It activates platelets and causes them to aggregate Signup and view all the answers

What is unique about the name of Plasmalogens?

They have 'al' in their names Signup and view all the answers

What is the potency of Platelet-activating factor (PAF)?

It causes effects at concentrations as low as 10^(-11) mol/l Signup and view all the answers

What is the typical arrangement of fatty acids in phospholipids?

Saturated FA at carbon 1 and unsaturated FA at carbon 2 Signup and view all the answers

Where are most phospholipids synthesized in the cell?

Smooth endoplasmic reticulum (SER) Signup and view all the answers

What is the function of kinases in phospholipid synthesis?

To phosphorylate choline and ethanolamine Signup and view all the answers

What is the significance of choline reutilization?

It is important because the amount of choline synthesized de novo is insufficient Signup and view all the answers

What is the intermediate molecule formed during the synthesis of phosphatidylcholine and phosphatidylethanolamine?

CDP-choline and CDP-ethanolamine Signup and view all the answers

What is the final step in the synthesis of phosphatidylcholine and phosphatidylethanolamine?

Transfer of choline phosphate or ethanolamine phosphate to DAG Signup and view all the answers

What is the recommended daily intake of choline for men?

550 mg Signup and view all the answers

What is the primary function of surfactant in the lungs?

To decrease the surface tension of the alveoli Signup and view all the answers

What is the role of dipalmitoylphosphatidylcholine (DPPC) in the lungs?

To decrease the surface tension of the alveoli Signup and view all the answers

What is the significance of the L/S ratio in fetal lung maturity?

It is a measure of fetal lung maturity Signup and view all the answers

What is a major cause of neonatal deaths in Western countries?

Respiratory distress syndrome Signup and view all the answers

At what gestational age does the shift from sphingomyelin to DPPC synthesis occur in pneumocytes?

32 weeks Signup and view all the answers

What is the purpose of giving glucocorticoids to the mother shortly before delivery?

To accelerate lung maturation Signup and view all the answers

What is acute RDS caused by?

Infection, injury, or aspiration Signup and view all the answers

What is the result of enhanced enzyme activity in COPD?

Decreased elastic fibers in the alveolar wall Signup and view all the answers

What is the purpose of phosphatidylcholine synthesis in the liver?

To export PC in the bile and as a component of plasma lipoproteins Signup and view all the answers

What is the role of PS decarboxylase in phosphatidylcholine synthesis?

To decarboxylate phosphatidylserine to PE Signup and view all the answers

What is the methyl group donor in phosphatidylcholine synthesis?

S-adenosylmethionine Signup and view all the answers

What is the primary function of the base exchange reaction in mammalian tissues?

To produce phosphatidylserine required for membrane synthesis Signup and view all the answers

What is unique about the fatty acid composition of phosphatidylinositol?

It contains stearic acid on carbon 1 and arachidonic acid on carbon 2 of the glycerol Signup and view all the answers

What is the role of flippases and floppases in phospholipid asymmetry?

They maintain phospholipid asymmetry in the cell membrane through ATP-dependent enzymes Signup and view all the answers

What is the result of phospholipase C cleaving phosphatidylinositol 4,5-bisphosphate?

Signaling across the membrane Signup and view all the answers

What is the function of phosphatidylinositol in membranes?

It provides the substrate for prostaglandin synthesis Signup and view all the answers

What is the charge of phosphatidylserine and phosphatidylinositol?

Net negative Signup and view all the answers

Study Notes

Phospholipids

Phosphatidalethanolamine is abundant in nerve tissue and is similar in structure to phosphatidylethanolamine.
Phosphatidalcholine is abundant in heart muscle and is a quantitatively significant ether lipid in mammals.

Platelet-Activating Factor (PAF)

PAF is an ether glycerophospholipid with a saturated alkyl group in an ether link to carbon 1 and an acetyl residue at carbon 2 of the glycerol backbone.
PAF is synthesized and released by various cell types, binds to surface receptors, and triggers potent thrombotic and acute inflammatory events.
PAF activates inflammatory cells, mediates hypersensitivity, acute inflammatory, and anaphylactic reactions, causes platelets to aggregate and activate, and neutrophils and alveolar macrophages to generate superoxide radicals to kill bacteria.
PAF also lowers blood pressure and is one of the most potent bioactive molecules known, causing effects at concentrations as low as 10^−11 mol/L.

Sphingophospholipids

Sphingomyelin is a phospholipid with a backbone of the amino alcohol sphingosine, rather than glycerol.

Phosphatidylserine (PS)

PS is synthesized in mammalian tissues by the base exchange reaction, in which the ethanolamine of PE is exchanged for free serine.
PS has a net negative charge and is primarily found on the inner leaflet of the cell membrane.

Phosphatidylinositol (PI)

PI is synthesized from free inositol and CDP-DAG.
PI has a net negative charge and is primarily found on the inner leaflet of the cell membrane.
PI serves as a reservoir of arachidonic acid in membranes and provides the substrate for prostaglandin synthesis when required.

Signal Transduction

The phosphorylation of membrane-bound PI produces polyphosphoinositides, which play a role in signal transduction across membranes.
Cleavage of PIP2 by phospholipase C occurs in response to the binding of various neurotransmitters, hormones, and growth factors to G protein-coupled receptors on the cell membrane.

Phosphatidylcholine (PC)

PC is a major lipid component of lung surfactant, which is the extracellular fluid layer lining the alveoli.
PC serves to decrease the surface tension of this fluid layer, reducing the pressure needed to reinflate alveoli, thereby preventing alveolar collapse (atelectasis).
Fetal lung maturity can be gauged by determining the DPPC/sphingomyelin ratio in amniotic fluid.

Lung Maturity

Respiratory distress syndrome (RDS) in preterm infants is associated with insufficient surfactant production and/or secretion.
Lung maturation can be accelerated by giving the mother glucocorticoids shortly before delivery to induce expression of specific genes.
Postnatal administration of natural or synthetic surfactant is also used to treat RDS.

Phosphatidylcholine Synthesis

PC is synthesized from phosphatidylserine, which is decarboxylated to PE by PS decarboxylase.
PE then undergoes three methylation steps to produce PC.
S-adenosylmethionine is the methyl group donor.

Phospholipid Synthesis

Most phospholipids are synthesized in the smooth endoplasmic reticulum (SER).
Phospholipids are transported to the Golgi and then to membranes of organelles or the plasma membrane or are secreted from the cell by exocytosis.
Ether lipid synthesis from dihydroxyacetone phosphate begins in peroxisomes.

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Description

This quiz covers the structure and abundance of phospholipids, specifically phosphatidalethanolamine and phosphatidalcholine, in different tissues.