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
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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
what is glycosphingolipid structure
The glycosphingolipids differ from sphingomyelin in that they do not contain phosphate, and the polar head function is provided by a monosaccharide or oligosaccharide attached directly to the ceramide by an O-glycosidic bond .
The number and type of carbohydrate moieties present determine the type of glycosphingolipid.
what are neutral glycosphingolipids
The simplest neutral glycosphingolipids are the cerebrosides.
These are ceramide monosaccharides that contain either a molecule of galactose or glucose.
Cerebrosides are found predominantly in the brain and peripheral nerves,with high concentrations in the myelin sheath.
what are acidic glycosphingolipids
Acidic glycosphingolipids are negatively charged at physiologic pH.
The negative charge is provided by N-acetylneuraminic acid ([NANA], a sialic acid, in gangliosides or by sulfate groups in sulfatides
Gangliosides: are the most complex glycosphingolipids and are found primarily in the ganglion cells of the CNS, They are derivatives of ceramide oligosaccharides and contain one or more molecules of NANA
Sulfatides: These sulfoglycosphingolipids are sulfated galactocerebrosides that are negatively charged at physiologic pH. Sulfatides are found predominantly in the brain and kidneys.
what is glycosphingolipid synthesis
Synthesis of glycosphingolipids occurs primarily in the Golgi by sequential addition of glycosyl monomers transferred from UDP-sugar donors to the acceptor molecule
The enzymes involved in the synthesis of glycosphingolipids are glycosyltransferases that are specific for the type and location of the glycosidic bond formed
A sulfate group from the sulfate carrier 3ʹ-phosphoadenosine-5ʹ- phosphosulfate ([PAPS] is transfered by a sulfotransferase
what is glycosphingolipid degradation
in lysosomes, a number of specific enzymes catalyse hydrolysis of ester and glycosidic linkages of sphingolipids
sphingomyelins loose phosphocholine to give ceramide
glycolipids due to the action of various specific glycosidases get rid of the saccharidic component to give ceramide
ceramide is hydrolysed to fatty acid and sphingosine
sphingosine is broken down to phosphoethanolamine and palmitaldehyde that is oxidised to palmitate
what are sphingolipidoses
inherited defects in production of the enzymes that catabolise sphingolipids result in the accumulation of their substances in lysosomes-
leading to lysosomal damage and disruption of the cell
in the sphingolipidosis mainly the cells of the CNS are affected
diseases of sphingolipidoses
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what are EICOSANOIDS
EICOSANOIDS-are a family of polyunsaturated C20 fatty acid derivatives,
which act as local hormones and have a wide range of biological functions.
The major precursors are essential polyunsaturated fatty acids
– arachidonic acid
The eicosanoids include the prostaglandins, thromboxanes, prostacyclins and leukotrienes
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