Membrane Structure and Function Flashcards
outer leaflet
exposed to the external side
inner leaflet
exposed to the cytoplasmic side
leaflets can vary between
different parts of the membrane
phospholipid content, protein content, etc
the phospholipid bilayer undergoes
natural oscillation
glycerol backbone contains
3 OH groups
the 3 OH groups of glycerol are sites for
side chain attachment
the glycerol backbone is attached to
fatty acid tails
polar phosphate head
sphingosine backbone is usually O-linked to a
charged group and amide-linked to an acyl group, such as a fatty acid
when you have a FA attached to the glycerol=
nonpolar
when you have a phosphate attached to the glycerol=
polar
diffusion in saturated lipids
slow because it is tightly packed
diffusion in mixed saturated and unsaturated lipids
quick because there is spacing created because of the kinks and is therefore much more open and molecules can move quicker
membrane phospholipid bilayers serve as
semipermeable membranes
charged molecules cannot diffuse through
the lipid bilayer
O2, N2, H2O, and CO2 can
diffuse rapidly across the lipid bilayer
glycine and other amino acids cannot
diffuse across membranes
hydrophobic compounds can
diffuse across membranes
ex. estrogen
lipid contents of the plasma membrane are distributed
asymmetrically
lipid components found outside of the cell (3)
sphingomyelin
glycolipid
phosphatidylcholine
lipid components found ion the cytoplasmic leaflet (3)
phosphatidylserine
phosphotidylinositol
phosphatidylethanolamine
cholesterol distribution
symmetrically distributed amongst the outer and inner leaflet
phospholipids can be cleaved into products that function as important
intracellular second messangers
PIP2 is cleaved by phospholipase C to form
IP3
DAG
important in intracellular signaling
when phospholipids are dispersed in water, they naturally for
vesicles
multilammellar or monolayer/unilammellar
what happens when water and oil are mixed rapidly?
it is initially cloudy because vesicles are forming. eventually they will settle and separate
liposomes are
artificially prepared vesicles composed of a lipid bilayer
liposomes can be used to
administer and transport nutrients and pharmaceutical drugs in the body
homing peptides
can target molecules on the outside
liposomes have a protective layer against
immune destruction (prevents immune interaction and destruction)
liposomes contain a (6)
- protective layer against immune destruction
- DNA
- homing peptide
- drug crystalized in aqueous fluid
- lipid-soluble drug in bilayer
- lipid bilayer
pfizer and moderna mechanism of action
liposome contains RNA that codes the spike protein. spike protein will attach to the virus, produce spike protein, and the body will create an immune response to destroy the virus
bottom line of liposome mechanisms
many drugs use liposome technology to treat diseases
the alpha helix is a common structural feature of
transmembrane regions of integral membrane proteins
amino acids that make up the alpha helix are
uncharged to interact with the inner leaflet
membrane protein functions (4)
cell-cell contact/adhesion
receptor signaling systems
pores and channels (transport)
enzymes
absorption and synthesis of cholesterol is important and much is known about
hereditary problems
other components of the plasma membrane (2)
cholesterol
triglycerides
FRAP shows us that
proteins move within the plasma membrane
FRAP
protein is labeled with fluorescent dye, shine a laser beam on the plasma membrane, fluorescence is lost, but overtime, this area regains fluorescence because proteins move within this region that the laser bleached
flippase
ex. PS, PE
from the outer to the inner leaflet
floppase
ex. PC, SL
from the inner to the outer leaflet
flippase and floppase require
ATP because they move against a concentration gradient
scramblase
ex. cholesterol
transfers between the inner and outer leaflet
does not require ATP
scramblase mechanism
lipid bilayer of the ER
phospholipid synthesis adds to the cytosolic half of the bilayer
scramblase catalyzes flipping of phospholipid molecules
symmetric growth of both halves of the bilayer
flippase mechanism
asymmetric lipid bilayer of the plasma membrane
delivery of new membrane by exocytosis
flippase catalyzes flipping of specific phospholipids to cytoplasmic monolayer
lipid rafts are specialized domains predominately within plasma membranes of cells which
organize membrane proteins and glycolipids in groupings, having functional implications in terms of receptor trafficking, neurotransmission, and membrane fluidity
lipid rafts move as
unit instead of individual parts
lipid rafts differ from the plasma membrane as a whole by being enriched in
cholesterol and sphingolipids
lipid rafts tend to be resistant to
dissociation by detergents which can freely dissociate the fluid membrane sections
caveolae
invaginations of the plasma membrane
caveolae form from
lipid rafts
it has been proposed that lipid rafts play a role in cell signaling events for the (3)
b-cell antigen receptor
t-cell antigen receptor
IgE receptor
ultracentrifugation
used to separate different membrane bound compartments like mitochondria and nucleus
density gradient ultracentrifugation
used to separate biological membranes containing lipids (and having lower densities) from proteins (having higher densities)
electron microscopy
An EM has greater resolving power than a light microscope and can reveal the structure of smaller objects because electrons have wavelengths about 100,000 times shorter than visible light photons. They can achieve better than 50 pm resolution and magnifications of up to about 10,000,000x whereas ordinary, non-confocal light microscopes are limited by diffraction to about 200 nm resolution and useful magnifications below 2000x.
fluorescence microscopy
uses fluorescence and phosphorescence instead of, or in addition to, reflection and absorption to study properties of organic or inorganic substances
atomic force microscopy
very high-resolution type of scanning probe microscopy, with demonstrated resolution on the order of fractions of a nanometer, more than 1000x better than the optical diffraction limit
cell fractionation mechanism
due to centifugational force, large or verse dense particles move toward the bottom of a tube and form a pellet
cell structures can be separated into various fractions by spinning the suspension at increasing revolutions per minute. membranes and organelles from the resuspended pellets can then be further purified by density gradient centrifugation
detergents solubilize
membranes
detergent mechanism
detergent positions itself within the membrane so the membrane falls apart. it encapsulates the lipids so they cannot come back together
freeze faction is used to
split apart the membrane
cantilever deflection can trace
the topography, where proteins are located, etc
virus fusion to the plasma membrane
enveloped virus attaches to the cell membrane of recipient cell via receptors, and receptors on the surface of the virus, followed by fusion where the envelope blends with the cell membrane and releases its contents (genome) into the cell
enveloped viruses containing human pathogens
DNA viruses (ex. herpes) RNA viruses (ex. corona) retroviruses (ex. HIV)
coronavirus
spike protein binds to receptor on a mammalian cell to trigger fusion
ACE2 concentrates on the
airway epithelium cells
why does washing hands with soapy water work to reduce/ prevent infection?
using detergent to break down a membrane so viruses cannot bind to the membrane and fuse
