CH 12 Lipids and Cell Membranes P2 Flashcards
Schwann Cell
relatively low protein content
lipid-rich plasma membrane
The lipid rich plasma membrane of Schwann Cells serve as?
insulator
allow rapid transmission of nerve impulses
Myelination
when a Schwann Cell wraps around an axon
Multiple Sclerosis
demyelination disease.
impairs myelin assembly.
damages existing myelin.
Myelin
lipid-rich plasma membrane of Schwann Cell in peripheral nerves / oligodendrocyte in brain wrapped many times around axon / portion of neuron conducting electrical impulses.
Integral Membrane Proteins (IMPs)
embedded in hydrocarbon core of membrane
most traverse lipid bilayer
some composed of beta strands
Peripheral Membrane Proteins (PMPs)
bound to polar head groups of membrane lipids / exposed surfaces of IMPs
Membrane-Spanning Alpha Helices
common structural feature of IMPs
most common structural motif in membrane proteins
Bacteriorhodopsin
membrane-spanning alpha helix light-powered proton pump IMP: 7 membrane-spanning helices. predominantly hydrophobic polar charged residues found in cytoplasmic / extracellular regions
Beta Strand IMPs
form a pore in the membrane
Porin
beta strand-rich IMP.
outside interacts w/ hydrophobic interior of membrane - composed of hydrophobic AAs.
Inside - polar, filled w/ water.
hydrophobic and hydrophilic AAs in adj. positions.
The part of the protein embedded in the membrane can link?
protein to membrane surface
Prostaglandin H2 Synthase 1
only portion of enzyme embedded in membrane
catalyzes formation of prostaglandin H2 from arachidonic acid in 2 steps.
Cyclooxygenase (COX) activity of prostaglandin H2 synthase-1 is dependent on?
the channel connecting active site to membrane interior
Aspirin
inhibits cyclooxygenase activity, obstructs channel
transfers acetyl group to serine residue in prostaglandin H2 synthase-1
Hydrophilic Proteins
associate w/ membrane by attaching one of a variety of possible hydrophobic groups
Membrane Anchors
hydrophobic groups
covalently attached to proteins
tether to proteins in membrane
Transmembrane Helices: Alpha Helix
20 residues
can transverse bilayer
Hydrophobicity of AA can by quantified via:
determining free E req’d to transfer AA from hydrophobic to hydrophilic environment.
Window
examines protein seq by measuring free E by transferring 20 AA’s from hydrophobic to hydrophilic environment
Hydropathy Plot
free E plotted against 1st AA of the window
can ID potential membrane-spanning helices when seq’d
doesn’t req additional info for protein
Criterion Level of Hydropathy Plot
peaks > 84 kJ/mol-1 indicative of potential transmembrane helices
Glycophorin
5’ inside
3’ inside
Porin on the Hydropathy Plot
no strong peaks bc constructed from beta strands rather than alpha helices
Fluorescence Recovery After Photobleaching (FRAP)
allows measurement of lateral mobility of membrane components
FRAP Technique
membrane component attached to fluorescent molecule.
dye subsequently destroyed by high-intensity light on very small portion of membrane.
aka - bleached.
S = (4Dt)^1/2
mobility of fluorescently labeled component function of how rapidly bleached area recovers fluorescence. ave distance travelled (S) in time (t) depends on diffusion constant (D).
Lateral Diffusion of Proteins
depends on whether attached to other cellular extracellular components.
Fluid Mosaic Model
describes membranes as 2D soln’s of oriented lipids and globular proteins
The Fluid Mosaic Models allows ____ but not ___.
lateral movement
not rotation through membrane
Lipids serve as what things?
solvent
permeability barrier
Lipids diffuse how in membranes?
laterally (rapid)
Transverse diffusion (flip-flopping) of lipids is rare w/o
enzyme assistance
very slow w/o
Prohibiting transverse diffusion of lipids accounts for?
stability of membrane asymmetry.
Membrane fluidity is controlled by?
FA composition
cholesterol content
Membrane processes depend on
fluidity of membrane
Melting Temperature (Tm)
temp at which membrane transitions from highly ordered to very fluid
Tm is dependent on
FA length in membrane lipid
degree of cis unsaturation
Cholesterol helps maintain ____ in animals.
proper membrane fluidity
Phase-Transition
Tm - Melting for phospholipid membrane
packed ordered to random
Highly ordered packing of FA chains in a membrane is disrupted by?
cis db’s
Cholesterol disrupts ____ in FA chains.
tight packing
Lipid Rafts
highly dynamic complexes
formed btw cholesterol and specific lipids
conc. in small regions of membrane.
Cholesterol can form complexes w/?
sphingolipids
glycolipids
some GPI-anchored proteins
Lipid Rafts help
moderate membrane fluidity function in signal transduction
Outer and Inner Leaflets (faces) of all biological membranes have diff?
components
enzymatic activities from e/o.
All biological membranes are?
asymmetric
Na+ - K+ Pump
transports Na+ out and K+ in by hydrolyzing ATP on intracellular side of membrane
Eukaryotic cells contain _____ bounds by _____.
compartments
internal membranes
Bacterial Membranes
Gram Positive
Gram Negative
Gram Positive
bacteria, archaea.
single membrane surrounded by thick cell wall
Gram Negative
bacteria.
2 membranes.
cell wall (proteins / peptides / carbs) lie btw them.
Space btw 2 membranes - periplasm.
Gram-Staining of Gram-Positive Bacteria
retain violet stain in thick cell walls
Gram-Staining of Gram-Negative Bacteria
doesn’t retain stain well bc of thin cell walls
Plasma Membrane
single membrane / cell membrane of eukaryotic cells (besides plants)
_____ have membranes inside the cell that allow compartmentalization of function.
eukaryotic cells
Nuclear Envelope
double membrane connected to another membrane (ER) of eukaryotes
ETC takes place in the?
inner membrane of mitochondria
Membranes can fuse and separate so that cells and compartments can?
take up, transport, and release molecules
Receptor-Mediated Endocytosis
how cells acquire molecules from environment
Clathrin
protein
helps internalize receptors bound to cargo
Fusion of internal membranes allows the release of?
molecules like NT’s from the cell
Receptor-Mediated Endocytosis Transferrin
internalization of Fe-bound transferrin associated w/ transferrin receptor (TfR)
SNARE Proteins
facilitate membrane fusion by forming tightly coiled 4-helical bundles
Vesicle Formation by Receptor-Mediated Endocytosis
receptor binds on cell surface.
induces membrane invagination w/ assistance of specialized intracellular proteins (ex clathrin)
vesicle formed w/i cell.
NT Release
NT-containing synaptic vesicles arrayed near plasma membrane of nerve cell.
fuse w/ plasma membrane.
release NT into synaptic cleft.
Transferrin-Receptor Cycle
Fe-bound transferrin binds to TfR on cell surface.
Receptor-mediated endocytosis.
vesicle formation - endosome.
lumen of endosome acidified via H+ pumps.
Fe released from transferrin.
Fe through membrane channels, utilized by cell.
Complex repeats another cycle.
SNARE Proteins that bring the membranes close together to initiate fusion event?
syntaxin-1
SNAP25
Cardiolipin or phosphatidylglycerol
unusual structure compared to other phosphoglycerides
net charge of -2
inverted cone shape
Cardiolipin is often found in?
membranes of bacteria archaea
inner membranes of mitochondria
In mitochondria Cardiolipin is involved in?
structure / function of respirasome
Respirasome
essential in ATP synthesis
Proper synthesis and maintenance of Cardiolipin levels requires the enzyme
tafazzin
Tafazzin
catalyzes transfer of linoleate chains from phosphatidylcholine to immature cardiolipin.
Barth Syndrome
results from mutations that reduce catalytic activity in tafazzin
Barth Syndrome Symptoms
heart chamber dilation
exercise intolerance
impaired growth
malformed mitochondria w/ distorted inner membranes
poorly functioning respirasomes (improper assembly of protein complexes)
