Lipid Metabolism - Membrane Phospholipids Flashcards

Flashcards for reviewing key concepts related to membrane phospholipids, covering structure, biosynthesis, and related disorders.

What are the two major classes of membrane phospholipids?

Glycerophospholipids and Sphingolipids

What two molecules can phospholipid species combine with to be constructed?

Various fatty acids and polar head groups with the glycerol or sphingosine backbone.

What are the main lipid constituents of membranes?

Phospholipids

What is phosphatidic acid?

A derivative in which the phosphate is esterified with one OH group of glycerol, and the other two OH groups are esterified to two long-chain fatty acids (glycerophospholipids).

What is sphingomyelin?

A sphingolipid in which the phosphate is esterified to sphingosine (a complex amino alcohol) and an important membrane component.

What is a key difference between glycerophospholipids and sphingolipids regarding their hydrocarbon tails?

In glycerophospholipids, both tails are fatty acid chains. In sphingolipids, one is a fatty acid and the second is part of the sphingosine molecule.

Which glycerophospholipids are abundant in cell membranes?

Phosphatidylcholines (Lecithins)

What is the alternate name for Dipalmitoyl lecithin?

Dipalmitoylphosphatidylcholine (DPPC)

What is the function of Dipalmitoylphosphatidylcholine?

A major component of pulmonary surfactant, crucial for reducing surface tension in the lungs and preventing alveolar collapse.

Name two phospholipids found in cell membranes besides phosphatidylcholine.

Phosphatidylethanolamine (cephalin) and Phosphatidylserine

Where are sphingomyelins found in large quantities?

In the myelin sheath that surrounds nerve fibers.

What is the combination of sphingosine plus a fatty acid known as?

Ceramide

What is ceramide a precursor of?

All sphingolipids

What is the stereoisomer of sugar inositol present in phosphatidylinositol?

Myoinositol

What two molecules is Phosphatidylinositol 4,5-bisphosphate (PiP2) cleaved into, and what function do they serve?

Diacylglycerol and inositol trisphosphate; both act as internal signals or second messengers.

Where is cardiolipin found, and what is its function?

Only in mitochondria; essential for mitochondrial function.

What are phosphoacylglycerols containing only one acyl radical known as?

Lysophospholipids (e.g., lysophosphatidylcholine or lysolecithin)

Where do plasmalogens occur?

In the brain and muscle

What is the function of plasmalogens?

May have a protective effect against reactive oxygen species.

What are the four steps in the assembly of phospholipids from simple precursors?

Synthesis of the backbone molecule; attachment of fatty acid(s) to the backbone; addition of a hydrophilic head group; alteration or exchange of the head group.

Where does phospholipid synthesis occur in eukaryotic cells?

Primarily on the surfaces of the smooth endoplasmic reticulum and the mitochondrial inner membrane.

What two strategies do cells have for attaching phospholipid head groups?

Diacylglycerol activated with CDP and Head group activated with CDP.

What is the parent compound of common glycerophospholipids?

Phosphatidic acid

How is phosphatidylinositol synthesized?

By condensation of CDP-diacylglycerol with inositol

How does the synthesis of phosphatidylcholine and phosphatidylethanolamine occur in mammals?

By activating the head group with CDP, followed by condensation of the head group with diacylglycerol (Strategy 2).

How is phosphatidylserine synthesized in mammals?

Derived from phosphatidylethanolamine via the head-group exchange reaction.

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

Causes blood platelet aggregation

What is the precursor from which all sphingolipids are formed?

Ceramide

What is the enzyme involved in the first step of sphingomyelin synthesis?

Serine palmitoyl transferase

What is the function of sphingomyelinase?

Hydrolyses sphingomyelins to ceramide and phosphorylcholine.

What is the cause and effect of Niemann-Pick disease?

A defect in the enzyme sphingomyelinase, causing accumulation of sphingomyelins in the liver and spleen, resulting in the enlargement of these organs, severe mental retardation.