Chapter 15: The Plasma Membrane Flashcards
1
Q
what are the 5 functions of membrane?
A
- boundary & selective permeability
- organization & localization
- proteins for transport processes
- receptors for signal detection
- cell-to-cell communication
2
Q
what are the main components of membranes?
A
phospholipids
3
Q
what are phospholipids made of?
A
- hydrocarbon tails
- glycerol
- phosphate
- PC, PS, PE, PI, sphingomyelin
4
Q
the phospholipid tails are
A
nonpolar & hydrophobic
5
Q
the phospholipid heads are
A
polar & hydrophilic
6
Q
membranes are impermeable to all
A
hydrophilic molecules
7
Q
membranes are permeable to small…
such as
A
hydrophobic molecules
steroid hormones
8
Q
membrane bilayers are
A
viscous fluids NOT solids
9
Q
the outer portion of the membrane is made of
A
PC, sphingomyelin, glycoproteins
10
Q
the inner portion of the membrane is composed of
A
PS, PE, PI
11
Q
the membrane is composed of about
A
50% proteins
12
Q
where is sphingomyelin synthesized?
A
in the Golgi
13
Q
what aids in creating the cell membrane potential?
A
- the negative charges of head groups
- ion concentration in the cytosol
14
Q
define phase transition
A
changing from one state to the other
15
Q
the plasma membrane state can change very quickly over a very
A
narrow temperature range
16
Q
what stabilizes both stages of a membrane’s phase transition?
A
cholesterol
17
Q
phase transition is aka
A
a cell’s fluidity
18
Q
___________ determines the proper function of the membrane
A
fluidity
19
Q
what are the 4 determinants of fluidity?
A
- fatty acid length
- type of fatty acid
- cholesterol
- lipid rafts
20
Q
how is fatty acid length a determinate of fluidity?
A
gel state is stabilized by van der Waals interactions
- short chains have less surface area for interaction
- short chain lipids melt at lower temperatures
21
Q
short-chain lipids are
A
more fluid
22
Q
long-chain lipids are
A
less fluid
23
Q
what are the 2 types of fatty acids?
A
- saturated fatty acids
- unsaturated fatty acids
24
Q
do saturated fatty acids increase or decrease membrane fluidity?
A
decrease
25
do unsaturated fatty acids increase or decrease membrane fluidity?
increase
26
why do unsaturated fatty acids increase membrane fluidity?
b/c they contain = bonds which increase the amount of proteins in the membrane and the passage of molecules
27
cholesterol at high temperatures
decreases fluidity
28
cholesterol at low temperatures
increases fluidity
29
lipid rafts are semisolid patches of
sphingomyelin, glycolipids, & cholesterol
30
lipid rafts are
discrete membrane domains
31
lipid rafts are thought to move
laterally within the plasma membrane
32
lipid rafts are thought to associate w/
specific proteins
33
what is the fluid mosaic model?
the plasma membrane w/ all the proteins, phospholipids, cholesterol. lipid rafts, and carbohydrate components
34
membrane proteins move _____ along the surface of the membrane
laterally
35
who observed the migration of labeled proteins and demonstrated the fluid mosaic model?
Frye and Edidin
36
what are 2 addition features of the plasma membrane?
1. glycocalyx
2. caveolae
37
describe glycocalyx
the carbohydrate coat around carbohydrate portions of glycolipids found on the OPM
38
glycocalyx protects cells from
ionic/mechanical stress
39
the glycocalyx is a barrier to
invading microorganisms
40
oligosaccharides participate in
cell-cell interactions
41
caveolae are
small invagination of the plasma membrane
42
caveolae are organized by
caveolin
43
caveolae carry out
receptor-mediated & receptor-independent endocytosis
44
what are the 3 main categories of membrane proteins?
1. integral
2. peripheral
3. lipid anchored
45
integral proteins either
completely or partially transect the membrane
46
what type of integral proteins DO NOT transect the mem. all the way?
monotopic
47
integral proteins are typically found on the
cytosolic side of the plasma membrane
48
peripheral proteins DO NOT interact w/
membrane lipids directly
49
peripheral proteins interact w/
integral proteins
| protein that is already in the mem.
50
lipid anchored proteins are
covalently linked to membrane phospholipid
51
lipid anchored proteins are inserted to the
cytosolic side of the membrane after being translated & folded
52
what is the exception of lipid anchored proteins? why?
- GPI anchors
- they are inserted to the outside of the membrane
53
what are 4 ways in which membrane proteins can be connected to the membrane?
1. amphipathic α-helix
2. hydrophobic loop
3. lipidation
4. electrostatic/ionic interactions
54
amphipathic α-helix protein connection to the membrane sits __________ to the membrane
parallel
55
lipidation is when a protein is
covalently bound to membrane lipids
56
explain the electrostatic/ionic interactions which some proteins can use to be connected w/ the plasma membrane
+ charged R groups of aa interact with - charged phospholipids
57
transmembrane proteins that form channels typically use
α-helices to cross the membrane
58
other transmembrane proteins that form channels can use
β-barrels
59
β-barrels are common in
aquaporins
| seen in kidney nephron
60
proteins are anchored to the plasma membrane by
lipids and glycolipids
61
what are the proteins involved in anchoring other proteins to the cytosolic side of the plasma membrane?
- Src
- Ras
62
Ras proteins makes connections through
disulfide bonds
63
Src proteins make connections through
ionic interactions
64
detergents solubilize
integral mem. proteins
65
detergents separate what from membranes?
proteins
66
detergents are synthesized to be
amphipathic
67
detergent that is considered to be 'mild' stringency
SDS
68
detergent that is considered to be 'high' stringency
Triton X-100
69
what are the 3 types of transport of molecules across the plasma membrane?
1. passive/simple diffusion
2. facilitated diffusion (passive transport)
3. active transport
70
what are the 2 types of active transport
1. indirect
2. direct
71
passive/simple diffusion require NO
energy input
72
what are the 3 main factors that affect the passive diffusion of molecules?
1. size
2. polarity
3. ion permeability
73
how can size affect the passive diffusion of molecules?
b/c the mem. is more permeable to small rather than large molecules
74
how can polarity affect the passive diffusion of molecules?
the mem. is permeable to nonpolar & less permeable to polar molecules
75
in general lipid bilayers are VERY
impermeable to ions
76
phospholipid bilayers are ONLY permeable to
- gases
- small hydrophobic molecules
77
facilitated diffusion is aka
passive transport
78
does facilitated diffusion require energy?
NO
79
facilitated diffusion can be described as movement in the direction of
relative concentrations
80
in facilitated diffusion molecules do NOT dissolve
in the membrane
81
facilitated diffusion is mediated by
proteins
82
facilitated diffusion typically transports
charged or polar molecules
83
give some examples of the charged or polar molecules that are transported through facilitated diffusion
- aa
- nucleosides
- sugars
- ions
84
what are the 2 classes of proteins that mediated facilitated diffusion?
1. carrier proteins
2. channel proteins
85
what are the 2 types of transporters?
1. uniport
2. cotransport
86
what are the 2 types of cotransport?
1. symport
2. antiport
87
describe the symport cotransport
the transport of two molecules in the SAME direction
88
describe the antiport cotransport
the transport of two molecules in OPPOSITE directions
89
what is an example of facilitated diffusion by carrier proteins?
the glucose transporter
90
the glucose transporter transports molecules in both directions and is dependent on where
[] of glucose is the highest
91
list the steps of the glucose transporter
1. glucose binds to the binding site on the outside of the cell
2. transporter changes conformations
3. glucose is released to the inside of the cell
4. transporter changed to original conformation
92
most ion channels are NOT permanently ___________, but are regulated by ________ that open in response to __________.
- open
- gates
- stimuli
93
regulated opening of ion channels mediates transmission of
electrical signals
94
what are the 2 types of ion channels?
1. voltage gated
2. ligand gated
95
voltage gated ion channels open via
membrane depolarization
96
ligand gated ion channels open via
the binding of a key
97
which type of transport is extremely rapid?
facilitated diffusion through ion channels
98
ligand-gated channels open in response to
binding of neurotransmitters/ signaling molecules
99
voltage-gated ion channels open in response to
changes in electrical potential across the plasma mem.
100
Na+ channels select Na+ atoms that are
bound to H2O
101
K+ channels select
dehydrated K+ atoms
102
isotonicity relies on
total solute concentration
103
________ is pumped out of the cell while _______ is pumped in
Na+
K+
104
which ion has the greatest effect on resting membrane potentials? why?
- K+
-b/c some K+ channels remain open
105
Na+ channels are open during which period of the action potential?
depolarization
106
what causes hyperpolarization?
the increase amount of open K+ channels
107
Ca2+ is stored where?
in the ER
108
list the 5 steps in the
1. arrival of action potential
2. voltage-gated Ca2+ channels open
3. Ca2+ enters axon terminal causing vesicles to bind to synaptic membrane
4. neurotransmitter is released into synaptic cleft
5. neurotransmitter binds to ligand-gated ion channels
6. post-synaptic membrane gets depolarized
109
what is an example of a unique pore?
porins
110
porins cross the membrane as
beta-barrel structures
111
porins enclose an
aqueous pore
112
porins do NOT allow
charged ions to cross
113
which types of porins are only found in some unique tissues?
aquaporins
114
aquaporins allow
rapid passage of large volumes of H2O
115
aquaporins are found in
- proximal tubules of kidneys
- erythrocytes
116
what is known as the transport of molecules against their concentration gradient?
active transport
117
facilitated diffusion is energetically
favorable
118
active transport is energetically
unfavorable
119
what are the 3 major functions made possible by active transport?
1. nutrient uptake
2. substance removal
3. maintain non-equilibrium intracellular []
120
active transport is based on an
energy source
121
active transport is regarded as either
direct or indirect
122
direct active transport is aka
primary active transport
123
indirect active transport is aka
secondary active transport
124
direct active transport is coupled directly to an
exergonic chemical reaction
125
indirect active transport depends on the
co-transport of 2 solutes
126
describe indirect active transport
the movement of a solute down its concentration gradient drives the movement of another solute against its concentrations gradient
127
with indirect active transport one of the solutes is most likely an
ion
128
which type of active transport is directly coupled to an exergonic chemical reaction?
direct/ primary active transport
129
what is the exergonic chemical reaction that direct active transport is coupled with?
hydrolysis of ATP
130
what is the name for the transport proteins that are driven by ATP hydrolysis?
ATPases ATPase Pumps
131
the largest family of membrane transporters consists of the
ABC transporters (ABC-type ATPases)
132
ABC transporters are characterized by a highly conserved ATP-binding domain known as
ATP-binding cassette
133
the Na+/K+ ATPase pump is used to regulate and maintain ________ in the cell
isotonicity
134
the Na+/K+ ATPase pump pumps _______ Na+ ____ and _________ K+ ________.
3
out
2
in
135
list the 9 steps in the sodium/potassium pump
1. pump open to inside
2. 3 Na+ bind
3. ATP phosphorylates causing a conformational change
4. 3 Na+ expel outside
5. pump is open to the outside
6. 2 K+ bind
7. dephosphorylation causes a conformational change
8. 2 K+ expel inside
9. pump returns to original shape
136
the ion gradients that are maintained by Na+/K+ pumps are essential for
transmission of action potentials
137
there is a higher concentration of what ion inside the cell?
K+
138
there is a higher concentration of which ion outside the cell?
Na+ & Cl-
139
what other pump is also powered by ATP hydrolysis?
Ca2+ pump
140
Ca2+ is pumped into the
ER lumen
141
since Ca2+ is pumped into the ER lumen Ca2+ _______________ concentrations are extremely low
intracellular
142
transient increases in cellular Ca2+ are important in
cell signaling
143
tonicity is a comparison of
2 aqueous systems
144
tonicity is the measure of the
osmotic pressure of 2 solutes separated by a semipermeable membrane
145
tonicity commonly describes a
response of cells immersed in solution
146
like osmotic pressure, tonicity is influenced by only
solutes that CANNOT cross the membrane
| - b/c these exert an osmotic pressure
147
why do solutes that can freely cross the membrane NOT affect tonicity?
b/c there will always be an equal concentration on both sides of the membrane
148
osmotic pressure is the pressure that must be applied to a solution to prevent the
inward flow of H2O across a semipermeable membrane
149
osmolarity (tonicity) is a term used to describe the concentration of a solute in terms of the
osmotic pressure it can exert
150
the Na+/K+ pump plays a crucial role in regulating
cell volume & maintaining osmolarity
151
what are the 3 sources of intracellular osmolarity?
1. macromolecules
2. small inorganic molecules
3. small inorganic ions
152
macromolecules contribute little to osmolarity b/c
they count as a single molecule
153
macromolecules are highly charged and attract many
inorganic ions of the opposite charge
154
b/c most small inorganic molecules are charged they attract
counterions
155
examples of small organic molecules include
sugars, amino acids, nucleotides
156
small inorganic ions leak
slowly across membrane into the cell
157
small inorganic ions are attracted to
- macromolecules
- small organic molecules
158
why does water tend to move in the direction of the cell cytoplasm?
- b/c of the intracellular sources of osmolarity
159
the Na+/K+ pump increases external osmolarity by
pumping out excess Na+
160
ABC transporters transport in
1 direction
161
in bacteria ABC transporters are used to drive the ______________ of _____________.
import
nutrients
162
in eukaryotes ABC transporters are used to transport toxic substances _____________ of the cell
out
163
ABC transporters can be problematic in the
delivery of chemotherapeutics
164
ATP phosphorylation causes the ABC transporters to be open to the
outside of the cell
165
mutations affecting ABC transporters are the molecular cause of
cystic fibrosis
166
CFTR stands for
cystic fibrosis transmembrane-conductance regulator
167
lack of function of Cl- channel results in the
accumulation of mucus in the respiratory & digestive tracks
168
indirect active transport is aka
secondary active transport
169
describe indirect active transport
the transport of 2 solutes
- one w/ its concentration gradient
- one against its concentration gradient
170
what is an example of a transporter that transports molecules in an indirect active transport manner?
the Na+/glucose transporter
171
describe the indirect active transport mechanism of the Na+/glucose transporter
the downward flow of Na+ provides enough energy to take up glucose and create high intracellular glucose concentrations
172
list the 6 steps in the active transport of glucose
1. pump open outside
2. Na+ ion binds (stimulating glucose binding)
3. conformational change
4. pump opens to inside
5. Na+ is released inside
6. glucose is released inside
7. pump returns to original position
173
with the Na+/ glucose pump how does the Na+ that's transported into the cell return to the outside of the cell?
by the Na+/K+ pump
174
explain the transport of glucose in the intestines
- active transport takes glucose to the apical surface of the intestinal epithelial
- glucose is then transferred to connective tissue and blood via facilitated diffusion
175
the transport of glucose in the intestines is driven by the
N+/K+ pump
176
what 4 types of transport are seen in erythrocytes?
- simple diffusion
- facilitated diffusion by carrier proteins
- facilitated diffusion by channel proteins
- active transport
177
describe the simple diffusion that is seen in erythrocytes?
cellular respiration: diffusion of O2 & CO2
178
describe the facilitated diffusion by carrier proteins that is seen in erythrocytes?
-glucose
- Cl- and HCO3- by anion exchange protein
179
describe the facilitated diffusion by channel proteins that is seen in erythrocytes?
- aquaporins
180
describe the active transport that is seen in erythrocytes?
Na+/K+ pump driven by ATP hydrolysis
