Lipids and membranes Flashcards
why are lipids insoluble?
because they are very heterogenous and hydrophobic
because lipids are insoluble what is a challenge?
transport and storage
what do lipids associate into?
bilayer, micelles, vesicles, droplets, and complex with proteins; they are rarely free in solution
what are the different classifications of lipids based on structure (5)
fatty acids, tricylglycerols, phospholipids, isoprenoids/steroids, glycolipids
what are fatty acids?
aliphatic carboxylic acids
what are tricylglycerols
3 fatty acids esterified to a glycerol
what are phospholipids?
phospho head groups attached to a diacylglycerol
what are steroids?
cholesterol
what are glycolipids?
a phospholipid that has a mono or disaccharide attached as a head group
what are the different classifications based on function?
cellular structures (membrane bilayers, vesicles), energy storage (trcylglycerols=fat), bioactivity (vitamins, hormones, 2ndary messengers)
what makes fatty acids amphipathic?
the carboxyl groups is hydrophilic and the the hydrocarbon tail is hydrophobic
What are the two types of fatty acids?
saturated (no double bonds) or unsaturated (double bonds)
what do most natural unsaturated FAs have?
unconjugated cis double bonds
how are most FAs found in the body?
esterified to cholesterol or glycerol or bound to an albumin
what are some FA derivatives?
soaps– are the Na+ salts of FAs
waxes are FAs esterified to long chain alcohols
prostoglandins, thromboxanes, leukotrienes
where are tricylglycerols found?
circulating lipoproteins or in insoluble cytosolic lipid droplets
how are TAGs in lipoproteins delivered in the blood to peripheral tissues?
as a fuel source or for storage in adipose tissue
in adipose tissue what can TAG in droplets be hydrolyzed to release?
glycerol and FFA for delivery into tissues or the liver
what is the major energy reservoir in the body?
TAGs
Glycerophospholipids variability of head groups?
cary by charge, cellular location and effects on membrane curvature and protein function. Gives them different characteristics
what do phospholipids primarily compose?
cellular membranes and vesicles
what are phospholipids pre-cursors of?
lipid 2ndary messengers
position specific cleavage of PIP2 by phospholipases generates bioactive molecules such as diacylglycerol
what are sphingomyelin and glycosphingolipids?
contain a sphingo backbone and have signalling and recognition roles and are abundant in the brain
what is specific about glycosphingolipids?
they are synthesized and degraded strictly in ordered pathways: genetic defects in lysosomal GSL degradation causes severe neurodegenerative diseases
what does cholesterol play an important role in?
maintaining lipid bilayer fluidity, and is a precursor of bile acids, steroid hormones and vitamin D, it is highly insoluble and must be transported in lipoproteins imbalances in which cause atheroclerosis and vascular diseases
what coordinates intercellular transport and regulation of cholesterol?
the liver!
is cholesterol excreted or degraded in humans?
excreted
what are isoprenoids derived from?
cholesterol intermediates–dolichol and ubq
what happens when lipids meet water?
they spontaneously associate due to their amphilic or hydrophobic nature, adopt many different structures dependent on size, shape and charge
what are the different structures lipids can form?
Droplets (TAGs) micelles (FFAs, lyso-PLs) vesicles (PLs) bilayers (PLs) monolayers (air-water interface)
what can micelle-forming lipids act as?
detergents (SDS)
what type of movement is allowed in lipid bilayers?
lateral diffusion and rotation but not flip floping in order to maintain asymmetry
what are integral membrane proteins?
embedded in the layer, interact with hydrophobic tails, you can’t get them out unless u solubilize the membrane
what are peripheral proteins?
attached using electrostatic force to outside of membrane
how do cis double bonds affect lipid bilayers?
decrease the melting point of crystalline PLs in lipid bilayers because membranes must be fluid at room T
what increases membrane fluidity?
the degree of FA unsaturation, length decreases it
how does cholesterol influence membrane fluidity?
smooths the transition between solid and liquid PL phases
modulates fluidity
what can integral membrane proteins span the bilayer as?
alpha helices (mammals) and beta barrels (bacteria)
what do cytoskeletal proteins do?
restrict lateral motion of proteins in vivo
what do GPI linkages do?
can very easily make a soluble nonmembrane protein into a membrane protein
what are lipid membrane domains?
relatively transient lateral regions within membrane bilayers that have distinct lipid/protein compositions and functions
what do lipid rafts tend to be like?
thicker, less fluid, lots of cholesterol, sphingolipids, and fatty acylated proteins
