phospholipids -Brar Flashcards
What is the structure of a phospholipid?
2 classes:
- glycerophospholipids: glycerol backbone with FA chains on C1 and C2 and a phosphate group on C3
- -> when nothing is attached to the phosphate=”phosphatidic acid”=precursor for others
- other phospholipids can be formed from phosphatidic acid and an alcohol –> serene, etanolamine, choline, inositol - sphingosine backbone–> “spingolipids”
What is the structure of cardiolipin and what is its role in the cell?
2 molecules of phosphatidic acid esterfies through their phosphate group to an additional glycerol
–> it is antigenic
found in the inner mitochondrial membrane–> crucial in mitochondrial activity
abnormal cardiolipins associated with alzheimers and parkinsons
also barth syndrome–> infantile cardiomyopathy linked to an X chromosome defect in cardiolipin processing gene
What is the structure and function of platelet activating factor?
ether glycerophospholipid with a saturated alkyl group with a link to carbon 1 (usually 16-18 carbons long)
Carbon 2 has an acetyl group instead of a fatty acid group
PAF is produced by many different type of cells by the action of phospholipase A2 on phosphatidylcholine
Some functions include
Activating inflammatory cells
Mediates hypersensitivity, acute inflammatory and anaphylactic reactions
Also causes platelets to aggregate and degranulate
Promotes the generation of superoxide radicals from neutrophils and alveolar macrophages
PAF is considered to be one of the most potent bioactive compounds
Can elicit a biological response at concentrations as low as 10-12 mol/l
Describe the process of phospholipid synthesis
synthesized in the smooth ER and transported to the Golgi and then to membranes of organelles or to the plasma membrane
requires either:
- donation of phosphatidic acid from CDP-diacylglycerol or (CTP + phosphatidic acid–> CDP-diacylglycerol)
- donation of phosphomonoester of the alcohol from CDP-alcohol to 1,2, diacylglycerol
phosphatidic acid=precursor for other phospholipids –> precursor for TAGs
-made in all cells except mature RBCs
Describe the process of phospholipid synthesis
synthesized in the smooth ER and transported to the Golgi and then to membranes of organelles or to the plasma membrane
requires either:
- donation of phosphatidic acid from CDP-diacylglycerol or (CTP + phosphatidic acid–> CDP-diacylglycerol)
- donation of phosphomonoester of the alcohol from CDP-alcohol to 1,2, diacylglycerol
phosphatidic acid=precursor for other phospholipids –> precursor for TAGs
-made in all cells except mature RBCs
What is the major component of lung surfactant?
DPPC ==> dipalmitoylphosphatidylcholine
palmitate at C1 andC2 of glycerol backbone
What is the major component of lung surfactant?
DPPC ==> dipalmitoylphosphatidylcholine
palmitate at C1 andC2 of glycerol backbone
What is the structure and function of phosphatidylinositol (PI)?
stearic acid at C1 and arachidonic acid at C2
–> reservoir of arachidonic acid –> used for prostaglandin synthesis
* important in signal transduciton
hormone binds to Gq –> GTP binds to alpha subunit and activates it–> PLC activated —> cleaves PIP2 into IP3 and diacylglycerol –> IP3 travels to the ER and binds to a receptor opening a Ca2+ channel–> Ca2+ and diacylglycerol activate PKC to phosphorylate proteins
What is the structure and function of phosphatidylinositol (PI)?
stearic acid at C1 and arachidonic acid at C2
–> reservoir of arachidonic acid –> used for prostaglandin synthesis
* important in signal transduciton
hormone binds to Gq –> GTP binds to alpha subunit and activates it–> PLC activated —> cleaves PIP2 into IP3 and diacylglycerol –> IP3 travels to the ER and binds to a receptor opening a Ca2+ channel–> Ca2+ and diacylglycerol activate PKC to phosphorylate proteins
Phospholipase activity and their site of action
phospholipases are found in all tissues==> hydrolyze the phosphodiester bonds of phosphoglycerides sat specific sites.
–> can degrade and remodel phospholipids
Phospholipase A1: cleaves the ester bond of C1 of a phospholipid. present in many tissues
A2: cleave the ester bond of C2–> in many tissues and in pancreatic juice
acts on phosphatidylinositol releasing arachidonic acid
-trypsin activates the pancreatic release of A2 and glucocorticoids inhibit its release
C: cleave just before the P on the C3. found in liver and lysosomes and in the alpha-toxin of clostridia
D: cleaved just beyond the P of C3 group (before the O-R===> found mostly in plants
What is the structure of a sphingolipid ?
a sphingosine backbone formed from a serine and a fatty acid
don’t have a phosphate group but have an amino group
Ceramide
a sphingosine with a single acyl group attached via an amide linkage is a ceramide
can be further altered by the addition of groups to the terminal OH
ex: sphingomyelin=important in neurons
cerebrosides:
have a glucose or galactose connected to the terminal OH group by a glycosidic bond
important in cerebral/nervous tissue
What are eicosanoids?
prostaglandins, thromboxanes and leukotrienes
originate from 20 C long PUFAs
Potent compounds
Produced in very small amounts in almost all tissues (rather than specialized glands)
Act locally (instead of being transported by blood to distant sites)
Are not stored
Extremely short half life (rapidly metabolized to inactive products)
Plasma and nuclear membranes mediate the action of eicosanoids
Which FA is the precursor for PGs?
linoleic acid
it is elongated and desaturated to arachidonic acid
- occurs in the ER
- requires 2 NADH and 2 O2