week 2 reading Flashcards
phosphatidylserine: unique characteristic
negatively-charged
lipid bilayer: how is it held together?
noncovalent interactions
sphingomyelin composition
fatty acid-NH2
phosphocholine-OH
sphingosone composition
amino + 2 -OH groups
cholesterol orientation
-OH groups close to polar heads of adjacent phospholipids
sterol composition
steroids with polar -OH, nonpolar hydrocarbon chains
spontaneous bilayer formation
shape and amphiphilic nature allows phospholipids to spontaneously form bilayers in aqueous environments
self-sealing properties
small tear exposes free edge to water
energetically unfavorable
flip-flop process
monolayer migration, very slow bc hydrophilic heads must enter and pass through hydrophobic core
(very rare)
flip-flop process exception
cholesterol
rapid location change within monolayer
rapid lateral diffusion: takes one second to diffuse length of cell
individual lipid molecules rotate about long axis, have flexible hydrocarbons
rapid location change within monolayer: problem
synthetic bilayers’ individual phospholipids are confined to their own membranes
- asymmetric expansion b/c molecules are only made in cytosolic layer of ER, can’t migrate to non-cytosolic membrane
fluidity: hydrocarbon chain length
lower temperature needed for shorter hydrocarbon chains, unsaturated chains
fluidity: shorter chains
shorter chains have less interaction between hydrocarbon tails in both same and opposite monolayer
fluidity favored by:
cis bonds
- kinks, tight packing
sterols: modulate bilayer properties
enhance permeability-barrier properties
- cholesterol interacts so -OH is by polar heads of phospholipids by polar heads to stiffen hydrocarbon chains closest to polar heads
- decreases permeability in small water-soluble molecules
- doesn’t affect fluidity
TM proteins
cross bilayer in alpha helix
- single or multipass
- peptide bonds driven to form hydrogen bonds bc bonds are polar and H2O is absent in bilayer
beta barrels
form channels
all hydrogen bonds must be satisfied
outside = hydrophobic
sheet exposing edge is unfavorable
glycosylation
oligosaccharides on non-cytosolic side
cytosol is a reducing environment
membrane asymmetry: functional importance
- converting extracellular signals to intracellular
- cytosolic proteins binding to specific head groups in cytosolic monolayer
- phospholipases activated by extracellular signals cleave certain phospholipid molecules: generated fragments act as short-lived intracellular messengers
lipid kinase function in asymmetry
can add phosphate groups to inositol rings to create binding sites
- recruit cytosolic proteins to membrane
phospholipase c function
intracellular messenger
- cleaves inositol phospholipid into two fragments
- one stays in membrane to activate PKC, one enters cytosol to stimulate Ca2+ release from ER
glycolipids
always on non-cytosolic leaflet
- protection from harsh conditions
- electric fields affect ion concentrations
- cell-recognition processes
membrane transport: principles
protein-free lipid bilayers are impermeable to ions
rate of diffusion varies based on hydrophobicity
- more nonpolar = more rapid diffusion
- smaller = faster diffusion
passive transport
downhill via concentration gradient
active transport
uphill via ion gradient or ATP hydrolysis
coupled transporters
use energy from concentration gradient to couple uphill transport of 1 solute to downhill transport of another
p-type pump
self-phosphorylate during pumping cycle
ATP –> ADP + Pi — Pi binds to pump
includes ion pumps
ABC transporters
need ATP
ATP binds to each side and separates to make channel
small, organic molecule transport
V-type
transports H+ into organelles
ATP synthase, ATP hydrolysis
