10.2 Structural Lipids in Membranes Flashcards
Biological membrane
double layer of lipids that acts as a barrier to polar molecules and ions
membrane lipids are
amphipathic- one end of the molecule is hydrophobic, the other hydrophilic
hydrophobic regions associate with each other
hydrophilic regions associate with water
4 General types of Membrane Lipids
phospholipids
glycolipids
archaeal tetraether lipids
sterols
phospholipids
have hydrophobic regions composed of 2 fatty acids joined to glycerol or sphingosine
glycolipids
contain a simple sugar or a complex oligosaccharide at the polar ends
archaeal tetraether lipids
have two very long alkyl chains ether-linked to glycerol at both ends
sterols
compounds characterized by a rigid system of four fused hydrocarbon rings
glycerophospholipids are derivatives of
phosphatidic acid
glycerophospholipids (phosphoglycerides)
membranes lipids in which two fatty acids are attached in ester linkage to the first and second carbons of glycerol, and a highly polar or charged group is attached through a phosphodiester linkage to the third carbon
glycerophospholipids are named as derivatives of phosphatidic acid
a phosphodiester bond joins the head group to glycerol
the phosphate group can bear a negative, neutral, or positive charge
phosphatidyl+ head group
the fatty acids in glycerophospholipids
can be any of a wide variety
in general, glycerophospholipids contain:
-a C16 or C18 saturated fatty acid at C1
-a C18 or C20 unsaturated fatty acid at C2
some glycerophospholipids have ether-linked fatty acids
ether lipids: one of the two acyl chains is attached to glycerol in ether, rather than ester, linkage
-chain may be saturated
-chain may contain a double bond between C1 and C2 as in plasmalogens
-vertebrate heart tissue is uniquely enriched with ether lipids
-functional significance is unknown (they are resistant to some phospholipases)
platelet-activating factor
an ETHER lipids that serves as a potent molecular signal
platelet-activating factor is released from
leukocytes called basophils
platelet-activating factor stimulates
platelet aggregation and serotonin release
plays a role in inflammation and the allergic response
(active lipid- not necessarily a membrane lipid)
galactolipids
member of the glycolipids group that predominate in plant cells
-one or two galactose residues are connected by a glycosidic linkage to C3 of a 1,2-diacylglycerol
sphingolipids are derivatives of
sphingosine
sphingolipids
large class of membrane phospholipids and glycolipids
-have a polar head group and two nonpolar tails
-contain NO glycerol
-contain one molecule of the long-chain amino alcohol sphingosine or one of its derivatives
ceramides are the
structural parent of all sphingolipids
C1, C2, and C3 of sphingosine are structurally analogous of the three carbons of glycerol in glyceorphospholipids
ceramide
compound resulting when a fatty acid is attached in amide linkage to the -NH2 on C2
-structurally similar to a diacylglycerol
sphingomyelins
subclass of sphingolipids that contains phosphocholine or phosophoethanolamine as their polar head group
glycosphingolipids
have had groups with 1+ sugars connected directly to the -OH at C1 of the ceramide moiety
-does NOT contain phosphate
-occur largely in the outer face of plasma membranes
cerebrosides
have a single sugar linked to ceramide
-those with galactose are found in the plasma membranes of cells in neural tissue
-those with glucose are found in the plasma membranes of cells in nonneural tissues
globosides
glycosphingolipids with 2+ sugars, usually D-glucose, D-galactose, or N-acetyl-D-galatosamine
sometimes called neutral glycolipids, as they have no net charge at pH 7
cerebrosides
globosides
gangliosides
have oligosaccharides as their polar head groups and 1+ residues of N-acetylneuraminic acid (Neu5Ac), a sialic acid, at the termini
1 sialic acid residue
GM (M for mono) series
2 sialic acid residues
GD (D for di) series
3 sialic acid residues
GT (T for tri) series and so on
sphingolipids at cell surfaces are sites of biological recognition
-prominent in the plasma membrane of neurons
-human blood groups are determined in part by the oligosaccharide head groups of these glycosphingolipids
phospholipids and sphingolipids are degraded in
lysosomes
phospholipases of the A type
remove one of the two fatty acids
lysophospholipases
remove the remaining fatty acid
lysosomal enzymes
catalyze the stepwise removal of sugar units of gangliosides yielding a ceramide
abnormal accumulations of membrane lipids
genetic defects in any of these hydrolytic enzymes leads to the accumulation of GANGLIOSIDES in the cell
sterols
structural lipids present in the membranes of most eukaryotic cells
have four fused carbon rings
steroid nucleus:
-consists of four fused rings
-almost planar
-relatively rigid
cholesterol
major sterol in animal tissues
-amphipathic
-polar head group
-nonpolar hydrocarbon body
-membrane constituents
-similar to stigmasterol in plants and ergosterol in fungi
sterols serve as precursors for products with specific biological activities
-steroid hormones regulate gene expression
bile acids
polar derivatives of cholesterol that emulsify dietary fats in the intestine to make them more readily accessible to digestive lipases
