Chapter 14 (plasma membrane) Flashcards
all cells are surrounded by a __________
plasma membrane
the plasma membrane defines the cell _______ and separates it from the _________
defines the cell boundary, and separates it from the environment
the plasma membrane is a ___ barrier, it determines the composition of the cytoplasm
it is a selective barrier
the fundamental structure of the membrane is the ________________
phospholipid biolayer
____________ embedded in the bilayer carry out specific functions, including ______________ of the molecules and _____________
protiens
selective transport
cell- cell regonition
mammalian red blood cells (__________) have been useful as a model for studies of membrane structure. these cells have no nuclei or internal membranes. the bilayer structure can be seen in the electron micrographs. the polar heads group appear as dark lines. the hydrophobic fatty acid chains in the center appear slightly stained
erythrocytes
animal cell plasma membranes have how many types of phospholipids?
5 types
the outer leaflet of the plasma membrane includes what phopspholipids?
phosphatidylcholine
the inner leaflet of the plasma membrane includes what phopspholipids?
phosphatidylethanolamine
phosphatidylserine
phosphatidylinositol
animal cell plasma membranes also contain :
glycolipids- only in the ___ leaflet, with carbohydrate portions exposed on the cell surface.
chloresterol- present in _____ molar amounts as phospholids
glycolipids are only in the OUTER LEAFLET
Cholesterol is present in about the same molar amounts as phospholipids
phospholipid structure is responsible for the _______________
the basic function of membranes- separting aqueous compartments
the bilayer interior consists of _________ fatty acid chains, so it is impermeable to water soluble molecules- ions and most biological molecules
hydrophobic fatty acids chains
bilayers are _____ not solids
bilayers are viscous fluids, they are not solid
the fatty acids have one or more double bonds, which makes ___ in the chain, and this keeps them from _______
kinks in the chain
these keep them from packing together
________ and ______ are free to diffuse laterally within the membrane
lipids and protiens
_________ and __________ tend to cluster in small patches of lipid rafts
cholesterol and sphingolipids (sphingomyelin and glycolipids)
most plasma membranes are about _ lipid and _______ protien by weight
50% lipids and 50 % protien
since proteins are much larger than lipids, this corresponds to about one protein per ________ molecules of lipid (within the plasma membrane)
one protien per 50-1000 molecules of lipid
they distinguished two classes of membrane protiens ________ and _________-
peripheral and integral
__________ movement of proteins and lipids in the membrane was first demonstrated in 1970. Human and mouse cells were fused in culture, then analyzed for membrane proteins using fluorescent antibodies
lateral movement
__________ associated with membranes through protein-protein interactions; often ___________. the bonds can be disrupted by ____________ (salts or extreme PH) many are part of the cortical cytoskeleton:spectrin, actin, band 4.1 ect
peripheral membrane protiens
ionic bonds
polar reagens
__________ : inserted into the lipid bilayer; they can be dissociated only by reagents that distrupt hyrophobic interactions
integral membrane protiens
_____are ___molecules with hydrophobic and hydrophillic groups that can solubilize these protiens
detergents are amphipathic molecules
________ integral protiens that span the lipid bilayer with portions exposed on both sides. They can be seen in electron micrographs of plasma membranes prepared by freeze-fracture technique
transmembrane protiens
the membrane- spanning portions are usually _______ of _________; they are inserted into the ER membrane during synthesis
alpha helices of hydrophobic amino acids
carbohydrate groups are added in the ER and Gogi; most are ____ with oligosaccharids exposed on the cell surface
glycoprotiens
_______ and ______ illustrate transmembrane protein structure
glycophorin and band 3
______ has a single transmembrane alpha helix
glycophorin
Band 3 is a transporter for HCO3- and Cl- ions, with _____ transmembrane alpha helixes
14 transmembrane alpha helices
some proteins are anchored in the plasma membrane by covalently attached lipids or glycolipids. _______________ are added to the C terminus of some proteins in the ER. These proteins are glycosylated and exposed on the cell surface. Other proteins are anchored in the inner leaflet by covalently attached lipids. they are translated on free ribosome and modified by myristic acid, prenyl groups, or palmitic acid. Many of these proteins (including Src and Ras) play roles in signal transmisison
GPI or called glycosylphosphatidylinositol
define glycocalyx
carbohydrate coat formed by the oligosaccharides of glycolipids and glycoprotiens
what is the function of the glycocalyx:
it protects the cell surface from ionic and mechanical stress and forms a barrier to invading microorganisms
Oligosaccharides of the glycocalyx particpate in a varitety of cell-cell interactions
many epithelial cells are polarized: plasma membranes are divided into ____ and _____ domains
apical and basolateral domains
in the small intestine, the ___________ is covered by microvilli that increase surface area for absorption
apical surface
the _______ is specialized to mediate transfer of absorbed nutrients to the blood
basolateral surface
to maintain its functions, the mobility of the plasma membrane protiens must be restricted to the appropriate _______
domains
___________ junctions separate the apical and basolateral domains
tight junctions
membrane proteins can move within each domain but can cross from one _____ to the other
domain
mobility of many plasma membrane proteins is restricted by association with the ____ or specialized ______
association with the cytoskeleton
or specialized lipid domains
transmembrane proteins anchored to the cytoskeleton have restricted mobility and may also act as barriers that _____ mobility of other membrane protiens
limit the mobility
______ are transient structure in which specific proteins can be concentrated to facilitate interactions.
they are enriched in GPI anchored protiens and transmembrane proteins involved in a variety of functions, including cell signaling, cell movement, and endocytosis
lipid rafts
_______ are small lipid rafts that start as invaginations of the plasma membrane, organized by caveolin.
The have been implicated in endocytosis, cell signaling, regulation of lipid trasport, and protection of the plasma membrane against mechanical stress
caveolae
plasma membranes are _ permeable to small molecules
selectively
what is the function of specific transport proteins (carrier and channel protiens)
they mediate passage of small molecules, allowing the cell to control the composition of its cytoplasm
passive diffusion of the membrane is defined as ???/
molecules dissolve in he phospholipid bilayer and diffuse across it
Passive diffusion: things to know
directions of transport is determined by the concentrations of the molecule inside and outside of the cell
net flow is always down the concentration gradient
only small, relatively hydrophobic molecules are able to passively diffuse across a phospholipid bilayer at significant rates
some examples of molecules that can do passive diffusion include:
Gases (O2 and CO2) hydrophobic molecules (steroid hormones) small polar but uncharged molcules (H20 and ethanol)
define facilitated diffusion.
direction of movement is determined by CONCENTRATION OF GRADIENTS
transport is mediated by protiens, which allow ____ and _____ to cross the plasma membrane (carbohydrates, amino acids, ions, and nucleosides)
polar and charged
carrier proteins do what?
bind molecules on one side of the membrane then undergo CONFORMATIONAL CHANGES that allow the molecule to pass through and be released on the other side
channel protiens from ___________ through the membrane, allowing free diffusion of any molecule of the appropriate size and charge
open pores
carrier proteins allow facilitated diffusion of ___, ______, and ________
sugars, amino acids, and nucleosides
the _____________ transporter has 12 alpha helical transmembrane segments (typical of many carrier protiens)
the glucose transporter
the transporter functions by alternating between two _____________-
by alternating between two conformation states
a glucose binding site is alternately exposed on the _ and the __ of the cell
inside and outside
glucose is rapidly metabolized in the cell so ________________ concentrations remain low and glucose is transported into the cell
intracellular glucose
glucose transport can also be reversed (true or false?)
true. because in liver cells when glucose is synthesized and released into the circulation
channel proteins such as __________ form open pores in the membrane that allow molecules to pass freely
porins
___ allow water molecules to cross the membrane rapidly. they are impermeable to charged ions, allowing passage of water without affecting electrochemical gradients
aquaporins
______________ are well studied in nerve and muscle cells, where their opening closing is responsible for transmission of electrical signals
ion channels
transport through ion channels is extremely ______; more than a million ions per second
rapid
ion channels are _______; specfic channel protiens allow passage of Na+, K+, Ca+2, and Cl-
they are highly selective
most ion channels “gates” that open only in response to a specific____
stimuli
define ligand- gated channels
they open in response to binding of NEUROTRANSMITTERS or other signalling molecules
define voltage gated channels
open in response to changes in ELECTRIC POTENTIAL across the plasma membrane
the role of ion channels in transmitting electric impulses was elucidated using giant _____ axons by Hodgkin and Huxley in 1952. electrodes inserted in the axon measured changes in membrane potential resultign form opening and closing of Na+ and K channels
squid
________ use energy from ATP hydrolysis to actively transport ions across the plasma membrane to maintain concentration of gradients.
thus the ionic composition of the cytoplasm is substantially different from that of extracellualr fluids.
ion pumps
because ions are electrically charged, pumping results in _______ gradients across the plasma membrane
electric
in resting squid axons there is an electric potential of 60 mV; the inside of the cell is _______with respect to the outside
inside of cell is negative with respect to the outside
Na+ is pumped _ out of the cell while K+ is pumed __
Na+ is pumped out of the cell while K+ is pumped In
the plasma membrane also contains open K+ channels, so the flow of K+ makes the largest contribution to the ______
resting membrane potential
as nerve impulses (___________) travel along axons, the membrane depolarizes
action potentials
memrane potential changes from ________ mV to _________ mV in less than a millisecond
-60mV to +30 mV
rapid potential changes results from rapid sequential opening an closing of _______ gated Na+ and K+ channels
voltage
depolarization of adjacent regions of the plasma membrane allows action _____ to travel the length of a nerve cell
action potentials
at the nerve end, neurotransmitters are released into the ________, where they bind to receptors on another nerve cell to open ____ channels
released into the SYNAPSE
to open LIGAN-GATED ION CHANNELS
nicotinic acetylcholine receptors in muscle cells are ________ gated channels
ligand gated channels
binding of acetylcholine opens a channel that allows rapid influx of Na+ which depolarizes the cell membrane and triggers an ___________–
action potential
biding of acetylcholine induces a conformation change in the __________–
receptor
voltage gated Na+ and K+ channels are more ________
selective
Na+ (.95A) is smaller than K+ (1.33A), and it is thought that the _______________
Na+ channel pore is to narrow for K+ or larger ions
How is K+ able to pass throuugh the voltage gated channel by itself but Na+ cant :(
well K+ ion can pass through because the channel is lined with carbonyl oxygen (C=O) atoms from the polypeptide backbone. This composition of the channel allows the displacement of the water to which K+ is bound, and thus K+ can pass through alone. Na+ is to small to interact and so it is bound to the water. Sine Na+ is bound to its water still it is to big and cant fit through the channel. Its a very sad ordeal.
voltage gated Na+ , K+, and Ca+2 channels belong to a family of related proteins play critical roles in signalling in all cell types. regulated opening and closing of ion channels is a sensitive and versatile mechanism for responding to a environmental _____
stimuli
in active transport, molecules are transported against their ________________.
Note energy is provide by a coupled reaction (such as ATP hydrolysis)
concentration gradients
ion pumps are examples of __________ transport
active
the NA+-K+ pump (or Na+-K+ ATPase) uses energy from ATP hydroloysis to transport Na+ and K+ _____ their electrochemical gradients
against
Na+-K+ pump operates by __ driven conformational changes
ATP
How many NA+ are transported out of the cell and how many K+ are transported into the cell for every ATP used
3 Na+ are transported out of the cell and 2 K+ are transported into the cell for every ATP
the Na+-K- pump uses nearly 25% of the ATP in many animal cells. The gradients are necessary for _____________ in nerve and muscle cells, to drive active transport of other molecules, and to maintain_______-
propagation of electric signals
osmotic balance and cell volume
the differences in ion concentrations balance the high concentrations of _________________ inside cells, equalizing osmotic pressure and ______________-
organic molecules
preventing the net influx of water
the Ca+2 pump is powered by ATP hydrolysis. Ca+2 is transported out of the cell or into the ER lumen so __________________________
intracellular Ca+2 concentrations are extremely low
transient, localized increases in intracellular Ca+2 are important in ______ (as in muscle contraction)
cell signaling
_________ in bacteria, yeast and plant cells actively transport H+ out of the cell
ions pumps
H+ is actively pumped out of the _____ lining cells, resulting in acidity of gastric juices
stomach
structurally distinct pumps actively transport H+ into _________________________
lysosomes and endosomes…
(just think how acidic these are. Make sense)
ATP synthases of mitochondria and chloroplast are another type of ____ pump.
These pumps operate in reverse, with the movement of ions down the electrochemical gradient used to drive ATP synthase
H+ pump
ABC transporters
have highly conserved ATP -binding domains or ATP binding cassets. more than 100 members of this family have been identified in both prokaryotic and eukaryotic cells. All ABC transporters used energy from ATP HYDROLYSIS to transport molecules in one direction. In prokaryotes they transport ____________ into the cell.
In both prokaryotic and eukaryotic cells they transport __________ out of the cell.
ABC transporter have two ATP binding domains and two________ domains.
the substrate binding site alternate between outward facing and inward facing , depending on ATP biding and hydrolysis
nutrient molecules
toxic substances
two transmembrane domains
some molecules can be transported _____________________ from coupled transport of another molecule in the energetically favorable direction
against their concentration gradients using energy
gradients established by Na+-K+ and H+ pumps provide a source for energy for _________________
active transport
____________ in the ________ of intestine epithelial cells transport two Na+ and one glucose into the cell
glucose transporter in the apical domain
flow of Na+ down its electrochemical gradient provides the energy that drives uptake of glucose against its ____________
concentration gradient
in the _____________, glucoses is transferred to the underlying connective tissue by facilitated diffusion
basolateral domain
the system is driven by the Na+-K+ pump, also found in the __________-
basolateral domain
uptake of ________ is an example of SYMPORT (also define symport)
glucose and Na+
symport is the transport of two molecules in the same direction
facilitated diffusion of glucose is an examples of UNIPORT (define uniport)
transport of a single molecule
define ANTIPORT
two molecules are transported in opposite directions
Ca+2 is exported from cells by the Ca+2 pump and by a Na+-Ca+2 antiporter that transports Na+ _____ and Ca+2 ______
Na+ in
and Ca+2 out
Na+-H+ antiporter transports Na+ _________________________________________________________
into the cell and H+ out , preventing acidification by H+ produced in metabolism
what does endocytosis do?
it allows cells to take up macromolecule, fluids, and large particles such as bacterial.
The material is surrounded by an area of plasma membrane, which buds off inside the cell to form a vesicle containing the ingested material
what does phagocytosis do?
(cell eating) it occurs in specialized cells types. Binding of a particle to receptors on the cell surface triggers extension of pseudopodia which surround the particle and fuse to for a large vessicle called a PHAGOSOME
what doe phagosomes do?
they fuse with lysosomes to form phagolysosomes, in which the material is digested by acid hydrolases
in mammals _______ and ______ (white blood cells) are the “professional phagocytes”
macrophages and neutrophils
these removed microorganisms from infected tissues, and macrophages eliminate aged or dead cells from tissue throughout the body
what is micropinocytosis
uptake of extracellular fluids in large vesicles
lamellipodia (sheet - like projections of the plasma membrane) curve into open cups, followed by membrane fusion to form a large intracellular vesicle
CLATHRIN-MEDIATED ENDOCYTOSIS is a mechanisms for ________ of specific macromolecules
selective uptake.
mechanisms of cargo selection, vesicle budding, and vesicle fusion are similar to those involved in vesicle transport in the secretory pathway
macromolecules bind to cell surface receptors in specialized regions called ___________.
the pits bud from the membrane with the help of ___________, to form small ___________, these then fuse with early endosomes
clathrin-coated pits
help of DYNAMIN, to form small CLATHRIN-COATED VESICLES
macromolecules bind to cell surface receptors in specialized regions called ___________.
the pits bud from the membrane with the help of ___________, to form small ___________, these then fuse with early endosomes
clathrin-coated pits
help of DYNAMIN, to form small CLATHRIN-COATED VESICLES
___________ endocytosis was first studied in patients with familial hypercholesterolemia (FH)
cathrin-mediated
choleserol is transported through the bloodstream mostly in the form of ______ , or____ particles
lipoprotien, or LDL particles
uptake of LDL requires binding to specific receptors in _____________–
clathrin-coated pits
LDL binding sites on normal cells were determined by adding ______ LDL to cell cultures.
Cells of FH patients did not bind LDL ________________ prevented them from binding LDL, or prevent the receptors form concentrating in the coated pits
radiolabeled
mutations in the LDL receptors prevented this
After internalization, clathrin coated vesicles shed their coats and fuse with early ________________-
These molecules are sorted, recycled to the plasma membrane, or remain in the __________ as they mature to ________ and _____ or degration
endosomes
early endosomes
late endosomes
lysosomes
Early endosomes have membrane H+ pumps which maintain acidic internal PH around _____????
This causes dissociation of many ligands from their receptors. Receptors can be returned to the plasma membrane via transport vesicles. Ligands such as LDL reamin and are degraded to release cholesterol. About 50% of the plasma membrane is internalized by receptor-medicated endocytosis every hour and must be replaced at an equivalent rate by recycling. MOST OF THE INTERNAL MEMBRANE IS REPLACED BY RECYCLING
6.0 to 6.2
clathrin- independent endocytosis (does or doens’t?) involve specific membrane receptors or coated vesicles
IT DOES NOT INVOLVE THIS
for example: macropinocytosis and internalization of caveolae are examples.
one pathway mediate uptake of GPI anchored plasma membrane proteins clustered in lipid rafts
