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
