Biochemistry Wk 5 Flashcards
what are phospholipids
Phospholipids are polar, ionic compounds composed of an alcohol that is attached by a phosphodiester bond to either diacylglycerol (DAG) or sphingosine.
what are the two classes of phospholipids
those that have glycerol as a backbone and those that have sphingosine .
what are glycerophospholipids
Phospholipids that contain glycerol are called glycerophospholipids.
Glycerophospholipids constitute the major class of phospholipids and are the predominant lipids in membranes.
All contain phosphatidic acid (PA), which is DAG with a phosphate group on carbon 3
more on Glycerophospholipids
PA is the simplest phosphoglyceride and is the precursor of the other members of this group
The phosphate group on PA can be esterified to a compound containing an alcohol group
examples of glycerophospholipids
serine and PA= phosphatidylserine
ethanolamine ‘ = phosphatidylethanolamine
what is phosphatidylcholine
in lung surfactant
In dipalmitoylphosphatidylcholine- DPPC, positions 1 and 2 on the glycerol are occupied by palmitate, a saturated LCFA.
DPPC, made and secreted by type II pneumocytes, is a major lipid component of lung surfactant
Surfactant serves to decrease the surface tension of this fluid layer, reducing the pressure needed to reinflate alveoli, thereby preventing alveolar collapse (atelectasis).
Surfactant is a complex mixture of lipids (90%) and proteins (10%), with DPPC being the major component for reducing surface tension
how can fetal lung capacity be gauged
Fetal lung maturity can be gauged by determining the DPPC/sphingomyelin ratio, usually written as L (for lecithin)/S, in amniotic fluid.
A value ≥2 is evidence of maturity, because it reflects the shift from sphingomyelin to DPPC synthesis that occurs in pneumocytes at ~32 weeks’ gestation
what is respiratory distress syndrome
Respiratory distress syndrome (RDS) in preterm infants is associated with insufficient surfactant production and/or secretion and is a significant cause of all neonatal deaths in Western countries.
Lung maturation can be accelerated by giving the mother glucocorticoids shortly before delivery to induce expression of specific genes.
what is phosphatidylinositol
PIP PIP2 PIP3 are minor components of plasma membranes and turnover stimulated by certain hormones
a specific phospholipase C, under hormonal control, hydrolysis phosphatidyl 4,5- bisphosphate to diacylglycerol and inositol 1,4,5 triphosphate both which have secondary messenger protein functions
Role of inositol and DAG in cell signalling
LOOK AT GOOD NOTES BOOK
Degradation of glycerophospholipids by phospholipases
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what are Sphingophospholipids
A long-chain-length FA (LCFA) is attached to the amino group of sphingosine through an amide linkage, producing a ceramide, which can also serve as a precursor of glycolipids.
The alcohol group at carbon 1 of sphingosine is esterified to phosphorylcholine, producing sphingomyelin, the only significant sphingophospholipid in humans.
Sphingomyelin is an important constituent of the myelin sheath of nerve fibers
the synthesis of sphingomyelin
Palmitoyl CoA condenses with serine and form sphinganine
The sphinganine is acylated at the amino group with one of a variety of LCFA and then desaturated to produce a ceramide
Phosphorylcholine from PC is transferred to the ceramide, producing sphingomyelin and DAG
what is Sphingomyelin degradation
Sphingomyelin is degraded by sphingomyelinase, a lysosomal enzyme that removes phosphorylcholine, leaving a ceramide.
The ceramide is, in turn, cleaved by ceramidase into sphingosine and a free FA
what is Niemann pick disease
sphingomyelinase deficiency
enlarged liver and spleen filled with lipid
severe intellectual disability and neurodegeneration
death in early childhood
