02 - Lipids & Membranes

Glycerophospholipids (phosphoglycerides), sphingolipids, and cholesterol

Glycerol backbone, with two hydroxyl groups being esterified with fatty acids (typically the FA on C-1 is saturated and C-2 is unsaturated) and the third hydroxyl group is attached to a polar alcohol via a phosphodiester linkage

It prevents the formation of closely packed, well-ordered crystals during solidification

Instead of having a glycerol, there is an amino alcohol; when there is a FA attached to the amino group via an amide linkage, the compound is called ceramide

Sphingomyelin; formed by esterification of the terminal hydroxyl group of ceramide with phosphoryl choline

Do not contain a phosphate and are formed by the attachment of a sugar residue to the terminal hydroxyl group of ceramide by a β glycosidic linkage

Cerebrosides and gangliosides; cerebosides have a glucose or galactose attached to the ceramide; gangliosides contain oligosaccharides

When this lipid is hydrolyzed by phospholipase C, it produces two signaling molecules, diacylglycerol and inositol triphosphate; diacylglycerol activates protein kinase C; inositol triphosphate increases intracellular calcium levels

Sphingomyelinase acts on sphingomyelin in the membrane and releases ceramine into the cell; ceramide is an important 2° messenger

Glycoproteins and glycolipids; only found on the exoplasmic surface of the cell

Diffuse parallel to the plane of the bilayer

Maintain the asymmetry of lipids in membranes by catalyzing unidirectional movement of specific lipids from one leaflet to another

In these cells the asymmetry of phospholipid distribution has broken down, and anionic phospholipids are exposed on the exoplasmic surface; this allows recognition by  scavenger receptors on circulating mononuclear phagocytes and initiates phagocytosis

Binds annexin V; fluorescein-labeled annexin V will bind to apoptotic cells but not to normal healthy cells

Exist in an α-helical formation, with hydrophobic AAs (Leu, Ile, Val, Trp, Phe, Tyr, Met) as the predominate AA; porins exist in β-barrel composed of antiparallel β sheets with hydrophobic AAs facing outside the barrel and hydrophilic AAs are facing inward forming the aqueous pore

There are other ways, but two main ways are: electrostatic binding between the negatively charged head groups of the membrane lipids and the positively charged regions of proteins; hydrophobic region containing nonpolar AAs at one end of the protein, which acts as an anchor in the membrane lipid