CHAPTER 14 Flashcards
plasma membrane function?
defines cell boundary, is a selective barrier that determines composition of cytoplasm, mediates interactions b/w cell and environment
what is the fundamental structure of the plasma membrane?
phospholipid bilayer
what do proteins in the bilayer do?
selective transport of molecules and cell to cell recognition
useful as a model for studies of the membrane structure ?
RBCs
why is it easier to study RBCs ?
they have no nuclei or internal membranes
animal cell membranes have 5 phospholipids?
outer leaflet-phosphatidylicholine, sphingomyelin
inner leaflet- phosphatidylethanolamine, phosphatidylserine,phosphatidylinositol
what other two compounds do animal cell membranes contain ?
glycolipids and cholesterol
what is the bilayer made up of ?
hydrophobic fatty acid chains(impermeable to water soluble fatty acid chains) and they have one or more double bonds which makes kinks in the chain and keeps them form packing together
what are sphingomyelin and glycolipids called together ?
sphingolipids
cholesterol and sphingolipids tend to cluster in small semisolid patches called?
lipid rafts
most plasma membranes are about 50% lipid and 50% protein by weight. T/F
true
what was proposed by singer and Nicolson in 1972?
fluid mosaic model
proteins associated with membranes through protein protein interactions with ionic bonds is?
peripheral membrane proteins
they are inserted into the lipid bilayer and can only be dissocated by reagents that disrupt hydrophobic interactions?
integral membrane proteins
amphipathic molecules with example?
hydrophobic and hydrophilic groups that can solubilize these proteins. eg- detergent
integral proteins that can span the lipid bilayer with portions exposed on both sides?
transmembrane proteins
what is the transmembrane protein composed of?
glycophorin and band 3
what does band 3 do?
transporter of HCO3^- and cl^- ions with 14 transmembrane alpha helices
what was the first transmembrane protein to be analyzed by X ray crystallography ?
photosynthetic reaction centre of rhodopseudomonas viridis
____ are added to the C terminus of some proteins in the ER.
GPI(glycosylphosphatidylinositol) anchors
carbohydrate coat formed by the oligosaccharides of glycolipids and glycoproteins?
glycocalyx
functiona of glycocalyx?
protects cell surface from ionic and mechanical stress and forms barrier to invading microrganims
what amendments were made to the fluid mosaic model?
1-mobility of many plasma membrane proteins is restricted
2-membranes are composed of distinct domains that have different structural and functional roles
the two domains the plasma membrane is divided into are ?
apical and basolateral domains
in the small intestine the basolateral surface is covered by microvilli that increase the surface area for absorption. T/F
false (apical surface)
the basolateral surface mediates transfer of absorbed nutrients to the blood. T/F
True
transient structures in which specific proteins can be concentrated to facilitate interactions and are enriched in GPI anchored proteins and transmembrane proteins are ?
lipid rafts
___ are small lipid rafts that start as invaginations of the plasma membrane organized by cave-in.
caveolae
caveolae function?
endocytosis, cell signalling, regulation of lipid transport, protection of plasma membrane against mechanical stress
facilitated diffusion?
direction of movement determined by concentration gradients, no energy required
how is facilitated diffusion mediated ?
by proteins which allow polar and charged molecules to cross the plasma membrane
____ ____ bind molecules on one side of the membrane and then undergo conformational changes that allow the molecule to pass through and be released on the other side.
carrier proteins
____ ____ form open pores through the membrane allowing free diffusion of any molecule of the app. size and charge.
channel proteins
what compounds do the carrier proteins allow through the membrane by facilitated diffusion ?
sugars, amino acids and nucleosides
what allows water molecules to cross the membrane rapidly and are impermeable to charged ions allowing passage of water without affecting electrochemical gradients?
aquaporins
present in nerve and muscle cells and responsible for transmission of electric signals?
ion channels
what ions do ion channels allow through them?
Na+, K+, Ca2+, Cl-
these channels open in response to binding of neurotransmitters ?
ligand gated channels
these channels open in response to changes in the electric potential across the plasma membrane?
voltage gated channels
the role of ion channels in transmitting electric impulses was first shown using giant squid axons by?
Hodgkin and Huxley in 1952
ion pumps use energy from ATP to actively transport ions across the plasma membrane to maintain concentration gradients. T/F
true
__ is pumped out of the cell while ___ is pumped in.
Na+,K+
nernest equation?
the relationship b/w ion conc. and membrane potential
V=RT/zF ln C o/C i
as nerve impulses travel along axons, membranes depolarize ?
action potential
membrane potential goes from what to what in less than a millisecond ?
- 60mV to +30mV
Na+ is smaller and narrower than K+. T/F
true
active transport?
molecules are transported against their conc. gradient and energy is provided by ATP
examples of active transport?
ion pumps and Na+K+ pump`
____ Na+ are transported out of the cell and ___K+ into the cell for every ATP(25%) used.
3,2
what do ion pumps in bacteria, yeasts and plant cells transport ?
H+
____ have highly conserved ATP binding domains or ATP binding cassettes
ABC transporters
how was the first eukaryote ABC transporter discovered?
product of the mdr(multi drug resistance) gene
what happens in cystic fibrosis?
defective Cl- transport in epithelial cells results in abnormally thick sticky mucus which obstructs respiratory passages
what protein does the cystic fibrosis gene encode?
CFTR cystic fibrosis transmembrane conductance regulator
symport?
transport of two molecules in the same direction eg-uptake of glucose and Na+
uniport?
transport of a single molecule eg-facilitated diffusion of glucose
antiport?
two molecules are transported in app. directions
endocytosis?
allows cells to take up macromolecules, fluids, and large particles such as bacteria
phagocytosis?
cell eating
phagosomes+lysosome ?
phagolysosomes
what are the professional phagocytes in mammals?
MACROPHAGES and neutrophils
macropinocytosis?
uptake of extracellular fluids in large vesicles
sheet like projections of the plasma membrane that curve into open cups followed by membrane fusion to form a large intracellular vesicle /
lamelliopodia
clathrin mediated endocytosis?
mechanism for selective uptake of specific macromolecules
