3. Membrane Structure Flashcards
encloses the cell, defines its boundaries, and maintains the essential differences between the cytosol and the extracellular environment
Plasma membrane
maintains the characteristics differences between the contents of each organelle and the cytosol
Plasma membrane
provides the basic fluid structure of the membrane and serves as a relatively impermeable barrier to the passage of most water-soluble molecules.
lipid bilayer
Tail of phospholipid
two hydrophobic hydrocarbon tails
protein sensors which transfer information across membrane
receptors
main phospholipids, two long-chain fatty acids
Phosphoglycerides
span the lipid bilayer and mediate nearly all the other functions of the membrane
Membrane proteins
most abundant membrane lipids
Phospholipids
50% of the mass of the most animal cell membranes
lipids
Head of phospholipid
Phosphate group
most common sphingolipid
Sphingomyelin
from sphingosine (long acyl chain with an amino group (NH2) & two hydroxyl groups (OH)
Spingolipids
It creates kink in the tail
cis-double bonds (unsaturated)
3 types of phospholycerides
Phosphatidylethanolamine
Phosphatidylserine
phosphatidylcholine
a fatty acid tail is attached to the amino group, and a phosphocholine group is attached to the terminal hydroxyl group
Spingomyelin
able to diffuse freely within the plane of a lipid bilayer
Lipid bilayer
phospholipid molecules in synthetic bilayers very rarely migrate from the monolayer on one side to that on the other
Flip-flop
Hydrophobic tails sandwitched
Bilayers
Tail inward characteristics
Spherical micelles
contains a rigid ring structure, to which attached a single polar hydroxyl group and a short nonpolar hydrocarbon chain
Cholesterol
the lipids tend to rearrange spontaneously to eliminate the free edge
Self-sealing property
resemble sphingolipids; sugars
Glycolipids
The lipid bilayer contains an unpaired electron whose spin creates a paramagnetic signal that can be detected by
electron spin resonance (ESR) spectrum
amphiphilic molecules spontaneously ___ to bury their hydrophobic tails in the interior
Aggregate
specialized membrane microdomains that serve as to organizing centers for assembly of signaling molecules
Lipid rafts
specialized for lipid storage that contain a giant liquid droplet
Fat cells or adipocytes
___ and ___ of the phospholipid molecules cause them to form bilayers spontaneously in aqueous environments.
Shape and amphiphilic nature
lipid molecules rapidly exchange places with their neighbors within a monolayer
Rapid lateral diffusion
catalyzes the rapid flip flop of phospholipids from one monolayer to the other
phospholipid translocators (flippases)
decrease mobility of the first few CH2 groups – makes lipid bilayer less deformable; decreases the permeability of the bilayer to small water-molecule * prevents the hydrocarbon chains from coming together and crystallizing
cholesterol
The lipid bilayer is a ____ fluid
Two-dimensional
modulates the properties of lipid bilayers and enhances the permeability-barrier properties
Cholesterol
How many carbon-long prenyl chains does archaea have?
20-25
storage of lipid
Lipid droplets
a change from a liquid state to a two-dimensional rigid crystalline state at a characteristic temperature
Phase transition
Outer monolayer of RBC
phosphatidylcholine & sphingomyelin
binds to the cytosolic face of the plasma membrane, where phosphatidylserine is concentrated, and requires this negatively charged phospholipid
protein kinase C (PKC)
assembly of signaling molecules, influence membrane fluidity and trafficking of membrane proteins, and regulate different cellular processes such as neurotransmission and receptor trafficking
Lipid rafts
Lipid bilayers can be built from molecules with similar features but __ __ __
different molecular designs
neutral lipids: exclusively hydrophobic molecules, and therefore aggregate into 3 dimensional droplets
Triacylglycerols and cholesterol esters
Important example of lipid kinase
phosphoinositide 3-kinase (PI 3-kinase)
Lipid droplets forms rapidly when cells are exposed to?
high conc. of fatty acids
Inner monolayer of RBC
phosphatidylethanolamine & phosphatidylserine
What is the importance of lipid asymmetry?
in converting extracellular signals into intracellular one
phospholipids in the cytosolic monolayer
phosphatidylinositol (PI)
cleaves an inositol phospholipid in the cytosolic monolayer of the plasma membrane to generate two fragments, one of which remains in the membrane and helps activate protein kinase C, while the other is released into the cytosol and stimulates the release of Ca2+ from the endoplasmic reticulum
Phospholipase C
translocate from the inner monolayer to the outer monolayer when cells undergo apoptosis
Phosphatidylserine
Sugar-containing lipid molecules that have the most extreme asymmetry in their membrane distribution. are found exclusively in the monolayer facing away from the cytosol
Glycolipids
charged glycolipids; important because of their electric effects
Gangliosides
exposed apical surface; may help to protect the membrane against the harsh conditions
Epithelial cells
asymmetric distribution of glycolipids in the bilayer results from the ____________ in the lumen of the Golgi apparatus
addition of sugar groups to the lipid molecules
performs most of the membrane’s specific tasks and therefore give each type of cell membrane its characteristic functional properties
Membrane proteins
Membrane proteins that extend through the lipid bilayer
Transmembrane proteins
Archor used by the membrane proteins that are entirely exposed at the external cell surface, by a covalent linkage
glycosylphosphatidylinositol; GPI anchor
do not extend into the hydrophobic interior of the lipid bilayer at all; they are instead bound to either face of the membrane by noncovalent interactions with other membrane proteins
membrane-associated proteins
do not extend into the hydrophobic interior of the lipid bilayer; bound to either face of the membrane by noncovalent interactions
Peripheral proteins
Membrane protein attachment by a fatty acid chain or a prenyl group
Myristoyl anchor
Palmitoyl anchor
Farnesyl anchor
always has a unique orientation in the membrane, reflects both the asymmetric way it is inserted into the lipid bilayer in the ER during its biosynthesis
Transmembrane protein
strands of a polypeptide chain to be arranges as a β sheet that is rolled up into a cylinder
multiple transmembrane
The hydrogen-bonding between peptide bonds is maximized if the polypeptide chain forms a regular α helix as it crosses the bilayer
How most membrane-spanning segments traverse the bilayer
Transmembrane proteins, the polypeptide chain crosses only once
single-pass transmembrane proteins
the polypeptide chain crosses multiple times
multipass transmembrane proteins
small amphiphilic molecules; more soluble in water than lipids
Detergents
used to localize potential α– helical membrane spanning segments in a polypeptide chain
hydropathy plots
Glycosylated: always present on the noncytosolic side of the membrane
oligosaccharide chains
Nanodiscs can be analyzed _____ to determine their structure
by single particle electron microscopy techniques
____ extensively coat the surface of all eukaryotic cells
Carbohydrates
Glycosylated: form on the noncytosolic side, where they can help stabilize either the folded structure of the polypeptide chain or its association with other polypeptide
Disulfide bonds
ionic (sodium dodecyl sulfate) or nonionic (octylglucoside and Triton)
Polar side
small, uniformly sized patches of membrane that are surrounded by a belt of protein, which covers the exposed edge of the bilayer to keep the patch in solution
Nanodiscs
surfactant concentration at which micelle formation is first seen in the solution
critical micelle concentration (CMC)
function to capture light energy and use it to pump H+ across the membrane
photosynthetic reaction center
able to move laterally within the membrane
Lateral diffusion
involves marking the membrane protein of interest with a specific fluorescent group (GFP)
fluorescence recovery after photobleaching (FRAP)
measures lateral diffusion rates of membrane proteins
fluorescence recovery after photobleaching (FRAP)
labeling individual membrane molecules and track their movement by video microscopy
single-particle tracking
certain plasma membrane enzymes and transport proteins are confined to the apical surface of the cells
epithelial cells
create nanoscale raft domains that function in signaling and membrane trafficking
protein-protein interactions in membranes
vesicle budding, cell movement, and cell division
shape is controlled dynamically
long, thin, flexible rod; it maintains the structural integrity and shape of the plasma membrane
Spectrin
enables the red cell to withstand the stress on its membrane as it is forced through narrow capillaries
spectrin-based cytoskeleton
vesicle budding, cell movement, and cell division
shape is controlled dynamically
