Chapter 11 Flashcards
(240 cards)
1
Q
The hydrophobic nature of the interior of the lipid bilayer is a barrier to what?
A
The passage of polar molecules
2
Q
The lipid bilayer functions to allow cells to accumulate solutes that are what?
A
Different from their surrounding extracellular fluid
3
Q
Cells exchange small molecules across its lipid bilayer for what processes? Give 3 processes
A
- The acquisition of nutrients
- Excretion of waste products
- The regulation of intracellular ion concentrations
4
Q
Synthetic protein-free lipid bilayers show differences in their relative permeability to what kind of molecules?
A
Small molecules
5
Q
Smaller and more hydrophobic/nonpolar a molecule is, what happens to the rate of diffusion across the membrane?
A
The faster its rate of diffusion across an artificial bilayer
6
Q
Small molecule transport will be driven by the difference in the solute concentration across the membrane with transport occuring down a molecules what?
A
Concentration gradient
7
Q
How quickly does small nonpolar molecules like oxygen and carbon dioxide cross a membrane?
A
Rapidly
8
Q
Charged molecules like sodium, potassium, magnesium or calcium are relatively impermeable to a lipid bilayer due to what?
A
Their charge and high degree of hydration
9
Q
The permeability coefficient and the calculated differences of a solute concentration across an artificial membrane can be used to calculate what?
A
A flow rate
10
Q
Name 5 hydrophobic molecules that can pass readily through a synthetic lipid bilayer
A
Oxygen, Carbon dioxide, Nitrogen, Steroids, Hormones
11
Q
Name 3 small uncharged polar molecules that can pass slowly through a synthetic lipid bilayer?
A
Water, Urea, Glycerol
12
Q
Name 2 large uncharged polar molecules that pass very slowly (unless helped by transport proteins) through a synthetic lipid bilayer?
A
Glucose, Sucrose
13
Q
Name six charged ions that are relatively impermeable to a lipid bilayer due their charge and high degree of hydration
A
Hydrogen, Nitrogen, HCO3, Potassium, Calcium, Choride, and Magnesium
14
Q
What is this structure?
A
Transporter
15
Q
What is this structure?
A
Channel protein
16
Q
Which one (channel protein or transporter) undergoes a conformational change when transporting materials into/out of a cell?
A
Transporter
17
Q
Which one (channel protein or transporter) is an aqueous pore?
A
Channel protein
18
Q
Which one (channel protein or transporter) moves material into/out of the cell at a quicker rate?
A
Channel protein
19
Q
The passage of polar molecules such as sugars, amino acids, nucleotides, cellular metabolites and ions across a membrane requires the use of what?
A
Transport proteins
20
Q
Transport proteins each transport a specific class of molecules and usually only what kind of molecular species?
A
A certain molecular species within that class
21
Q
All known transport proteins are what?
A
Multispanning transmembrane proteins
22
Q
The structural composition of transmembrane proteins allows for the transport of what kind of molecules across a hydrophobic lipid bilayer without making direct contact?
A
Small hydrophilic molecules
23
Q
What are the two kinds of membrane transport proteins?
A
- Transporters/carriers/permeases 2. Channels
24
Q
What kind of membrane transport protein binds to the solute being transported and undergo changes in conformation to transfer the molecule across the membrane?
A
Transporters
25
What kind of membrane transport protein only weakly interact with the transported molecule and essential act as an aqueous pore for transport
Channel proteins
26
Solute transport is therefore faster through a channel than through a what?
Membrane transporter
27
Identify A: What kind of transport is this? It is a small hydrophobic molecule that can pass readily through the lipid bilayer.
Simple diffusion
28
Identify B and X : What kind of transport is this? Is it channel mediated or transporter mediated? Is it passive transport or active transport?
Channel mediated; Passive transport
29
Identify C and X: What kind of transport is this? Is it channel mediated or transporter mediated? Is it passive transport or active transport?
Transporter mediated; Passive transport
30
Identify Y: What kind of transport is this? Is it active or passive transport?
Active transport
31
What kind of transport uses only transporters and requires energy input?
Active transport
32
What kind of transport uses either channels or transporters with the concentration gradient?
Passive transport
33
Which electrochemical gradient has no membrane potential?
A
34
Which electrochemical gradient has a negative membrane potential inside?
B
35
Which electrochemical gradient has a positive membrane potential inside?
C
36
Which one will transport it's materials more quickly? Which one will transport it's materials the slowest?
Fastest: B; Slowest: C
37
All channels, and many transporters, work by what?
Facilitated diffusion or passive transport
38
Passive transport is the passage of solutes across a membrane down their what?
Concentration gradient
39
For an uncharged molecule, transport is influenced by what only?
Concentration
40
For a charged molecule, what two things influences its transport across a membrane?
Concentration and the electrical potential difference
41
What is the combination of the membrane potential and concentration gradient?
'Electrochemical gradient'
42
If a solute is moving down its concentration gradient and with the electrical gradient the combined effect will be what?
Additive
43
If a solute is moving down its concentration gradient but against the electrical gradient the two properties will what?
Work against each other
44
Moving solutes against their electrochemical gradient requires the activity of what?
Membrane transporters
45
Moving solutes against their electrochemical gradient using membran transporters is an 'active' process that transports solutes by linking their passage to what?
ATP hydrolysis or an ion gradient
46
Passive transport of a molecule down its electrochemical gradient is facilited by what?
Reversible conformational changes in the membrane transporter proteins
47
Does a solute transported by membrane transporters get modified in any way?
No
48
What kind of transport in which the side the solute is delivered to is dependent on its concentration on each side of the lipid bilayer as well as the membrane potential for charged molecules
Passive transport
49
Changes in transporter conformation is not dependent on what?
Solute binding
50
Changes in transporter conformation occur at what?
Random
51
When is the rate of solute transport is maximal?
When all solute binding sites are occupied
52
Passive transport can be blocked by both what?
Competitive and noncompetitive inhibitors
53
Active transport is required to pump a solute against its what?
Electrochemical gradient
54
Active transporters depend on what for their transport activities?
A source of energy
55
Sources of energy for active transport can come from what three sources?
1. Coupling the transport of one solute to the downhill transport of another 2. The hydrolysis of ATP3. The coupling of transport to the energy derived from light (bacteria)
56
Identify A: What kind of active transporter is this?
Coupled Transporter
57
Identify B: What kind of active transporter is this?
ATP-Driven Pump
58
Identify C: What kind of active transporter is this?
Light Driven Pump
59
What is the process in which the movement of one solute is dependent on the movement of another?
Coupled transport
60
Coupled transporters function as what two things?
Symporters or antiporters
61
What transporter simultaneously transfers the 'transported' molecule along with its 'co-transported' molecule in the same direction?
Symporters (a.k.a co-transporters)
62
What transporter pumps the 'transported' molecule in the opposite direction of the 'co-transported' molecule?
Antiporters (a.k.a exchangers)
63
How do both symporters and antiporters work?
By harvesting the energy stored in the electrochemical gradient of the co-transported ion for the transport of another molecule
64
The free-energy derived from the movement of the co-transported ion down its electrochemical gradient is used to do what?
Drive another solute against its gradient
65
In the plasma membrane of mammalian cells, What is the cotransported ion?
Sodium
66
In bacteria, yeast and other membrane bound mammalian organelles the co-transported ion is a what?
Proton
67
Identify A: What kind of transporter is this?
Uniport
68
Identify B: What kind of transporter is this?
Symport
69
Identify C: What kind of transporter is this?
Antiporter
70
Which two transporters are coupled transporters?
B and C
71
The sodium-glucose symporter is found where in the body?
The plasma membrane of intestinal or kidney epithelial cells
72
The sodium-glucose pump undergoes what kind of change during the transport process?
Conformational change
73
In which state (A or B) is the transporter is open to the extracellular space allowing for sodium and glucose binding?
state A
74
During state A, when sodium binds it induces a conformational change that increases the transporters affinity for what?
Glucose
75
Only when both molecules are bound will the transporter open to the what for delivery?
The cytosol
76
The overall result of the sodium-glucose symporter is the transport of what into the cell?
Sodium and Glucose (sodium moving down its electrochemical gradient essentially dragging glucose along against its gradient)
77
For the system to continue to work, the cell must remove what in order to maintain the electrochemical gradient?
Intracellular sodium
78
What in the plasma membrane is responsible for maintaining the sodium gradient?
The ATP-driven sodium/potassium pump
79
Give an example of a proton-driven symporter in E. coli.
Lactose permease
80
The lactose permease is a what?
12 transmembrane spanning protein
81
Lactose permease pumps lactose across the plasma membrane into the cytosol along with a what?
A proton (the co-transported ion)
82
Binding and transport is what, with the passage of lactose dependent on proton transport?
Cooperative
83
Active transporters that are dependent on an electrochemical gradient must have a mechanism in place to do what?
Maintain the gradient
84
Transport of glucose into the cell also carries along what kind of ion?
Sodium
85
For the system to continue to work, the cell must maintain the what?
Sodium electrochemical gradient
86
In what kind of cells does the plasma membrane contain an ATP-driven sodium/potassium pump responsible for maintaining the sodium gradient?
Mammalian cells
87
In what kind of cells is the proton gradient maintained through the activity of a proton ATPase?
In bacteria, yeast and several intracellular organelles
88
Which cell (animal or plant) uses the sodium driven symport?
Animal cell
89
Which cell (animal or plant) uses the hydrogen driven symport?
Plant cell
90
What kind of active transporter use the energy stored in ATP to pump ions or other solutes across a membrane?
Transport ATPases
91
What are four types of ATP driven pumps?
1. P-type pumps2. F-type proton pumps3. V-type pumps4. ABC transporters
92
P-type pumps become what during the pumping cycle?
Phosphorylated
93
Many of the ion pumps involved in establishing and maintaining a what across membranes belong to the P-type pump class?
Gradient
94
What kind of pumps use a proton gradient to generate ATP?
F-type pumps
95
What is the other name for the F-type pump?
ATP synthases
96
Where are F-type pumps found?
1 Plasma membrane of bacteria2. The inner membrane of mitchondria3. The thylakoid membrane of chloroplasts
97
What kind of pumps are similar to F-type pumps but they pump protons into organelles to acidify their interior?
V-type pumps
98
Where are V-type pumps found?
1 Lysosomes2. Synaptic vesicles3. Plant vacuoles
99
V-type pumps are not involved in what?
ATP production
100
What kind of transporters pump small molecules across a cell membrane?
ABC transporters
101
All of ATP driven pumps can operate in what direction?
Reverse
102
Under conditions in which the electrochemical potential is reversed and cytosolic ATP levels are low, channels can work to synthesize ATP from what?
ADP
103
What kind of ATP driven pump is A?
P-type pump
104
What kind of ATP driven pump is B?
F-type (and V-type) proton pump
105
What kind of ATP driven pump is C?
ABC transporter
106
What kind of P-type pump is this?
Calcium (Ca2+)
107
What kind of ATP pump is a prototypical P-type pump?
The calcium ATPase pump
108
What kind of cells maintain a steep calcium gradient across their plasma membrane?
Eukaryotic
109
The calcium gradient is important for a cells response to what?
1. Extracellular signals (to initiate embryonic development)2. The stimulation of muscle contraction3. Triggering secretion in secretory cells
110
The calcium ATPase is localized to the plasma membrane and the what?
Sarcoplasmic reticulum (SR)
111
What is a specialized endoplasmic reticulum that serves as an intracellular store for calcium?
Sarcoplasmic reticulum (SR)
112
What is responsible for pumping calcium from the cytosol back into the SR after calcium stimulated muscle contraction?
The calcium ATPase
113
The function of the calcium channel is critical for what?
Muscle relaxation
114
The calcium pump has 10 transmembrane alpha helices with three of these forming the what?
central pore forming channel
115
In the unphosphorylated state, the channel is open to the cytosol allowing for how many calcium ions to bind?
2
116
Upon calcium binding, ATP is hydrolyzed and the terminal phosphate is transferred to a what?
an aspartic acid
117
The phosphorylation event in the calcium channel triggers a conformational change that disrupts calcium binding leading to calcium release to the what?
SR lumen
118
Phosphorylation is transient and its removal returns the channel to what state?
Calcium free
119
What kind of pump is this?
Sodium potassium pump
120
The sodium potassium pump is an example of what kind of pump?
P-type ATPase
121
Where is the sodium potassium pump found?
The plasma membrane of all animal cells
122
What is the sodium potassium pump function?
Maintaining the sodium gradient across the plasma membrane.
123
In what kind of cells is a sodium gradient critical as it is used by other membrane pumps for the transport of most nutrients into the cell
Mammalian cells
124
The sodium-potassium pump is an ATP-driven what? (symporter or antiporter?)
Antiporter
125
How many sodium ions does the sodium potassium pump - pump out of the cell?
3
126
How many potassium ions does the sodium potassium pump - pump into the cell?
2
127
The sodium-potassium pump moves 3 positively charged ions out of the cell for every two it pumps in, it has a minor role in establishing a what across the membrane?
An electrical potential
128
The sodium-potassium pump also maintains what by exporting sodium ions to counteract the influx of water by osmosis?
The osmotic balance
129
The sodium-potassium pump is inhibited by what which directly competes for potassium binding?
Ouabain
130
What are the steps outlining the workings of a sodium potassium pump?
1. Three sodium ions from inside the cell first bind to the transport protein.
2. A phosphate group is transferred from ATP to the transport protein causing it to change shape and release the sodium ions outside the cell.
3. Two potassium ions from outside the cell then bind to the transport protein.
4. As the phosphate is removed, the protein assumes its original shape and releases the potassium ions inside the cell.
131
What transporters typically contain six membrane-spanning domains and two ATPase domains?
ABC transporters
132
ABC transporters are characterized based on their what?
Polypeptide organization
133
What transporters are formed through the dimerization of two polypeptide chains each containing an ATPase domain?
Half transporters
134
The polypeptide organization of half transporters may be what? (2 answers)
Identical (homodimers) or they may be formed by multiple different polypeptides subunits
135
What transporters encode two ATPase domains in a single polypeptide unit
Full transporters
136
What are the largest family of membrane transport proteins?
Full transporters
137
What kind of transporter pumps inorganic ions, amino acids, mono and polysaccharides, peptides and even proteins across extra and intracellular membranes?
Full transporters
138
In bacteria, ABC transporters are involved in the import and export of what?
Molecules
139
In eukaryotes, ABC transporters are involved in exporting molecules from the cell and importing substrates into what?
Organelles (ER and mitochondria)
140
In gram negative bacteria (E. coli), ABC transporters localize where?
The inner membrane
141
In gram negative bacteria, solutes that can freely pass across the outer membrane interact with substrate specific binding proteins in what space?
The periplasmic space
142
Upon solute binding "shuttling" proteins undergo a conformational change that enables them to bind to the ABC transporters for what purpose?
Solute delivery
143
The ABC transporter actively transfers the molecule across the inner membrane in a what driven manner?
ATP dependent manner
144
Give the steps in the auxiliary transport system in bacteria
1. The solute diffuses through a channel protein in the outer membrane
2. A periplasmic substrate binding protein picks up the substance to be transported and carries it to the ABC transporter.
3. ATP binds to an ATP hydrolyzing enzyme and is broken down to ADP, phosphate and energy
4. The energy from the ATP powers the transport of the substrate across the membrane through the plasma membrane
145
What are not open all of the time rather a specific signal triggers a change in conformation which leads to its opening (i.e. gating)?
Ion channels
146
The channel pore narrows significantly in its what? It is a narrow opening that largely determines which ions can pass)
Selectivity filter
147
What has a pore lined with hydrophilic amino acids which form the channel opening and hydrophobic amino acids arranged along the outside of the channel to interact with the lipid bilayer.
The channel
148
Ion channels do not make what?
Aqueous 'holes' in the membrane;
149
Ion channels are highly selective in the whats that can pass through them?
Ions
150
Only what kind of ions (without their bound water) can pass through a specific channel?
The right size and charge
151
Ion channels fluctuate between what two states?
An open and closed state (based on the presence or absence of a specific stimulus)
152
What is the the property of the channel 'opening briefly' upon stimulation?
Gating
153
Which ion channel is open?
B
154
There are more than 100 different types of ion channels that differ from one another based what three characteristics?
1. Ion selectivity (the types of ions that can pass through a channel)2. Gating (the conditions that influence their opening and closing)3. Their abundance and subcellular localization
155
Give three kinds of stimuli that regulate channel gating
1. Voltage gating (Probability of opening is controlled by membrane potential)2. Ligand gating (Chemical ligand (molecule) binding controls channel opening)3. Stress gating (Mechanical forces placed on the channel controls opening)
156
What are two activities that contribute to the membrane potential?
Active electrogenic pumps and passive ion diffusion
157
The movement of ions across a membrane, if not exactly balanced by oppositely charged ions, can be detected as an accumulation of electric charge referred to as what?
The "membrane potential".
158
What results from a thin layer of ions sitting close to the membrane due to their attraction to their counterparts of the other side of the membrane. All that is required for the establishment of it is the movement of only a small fraction of the total charge?
Membrane potential
159
In what organelle does the membrane potential across the inner membrane is due to the activity of the electrogenic proton pumps?
In the mitochondria
160
In plants and fungi, what establishes the membrane potential across the plasma membrane
Proton pumps
161
High level of intracellular (-) charged organic molecules is balanced by the levels of what?
Intracellular K+
162
High intracellular K+ is generated by the what in the plasma membrane?
Na+-K+ pump
163
What channel in the plasma membrane randomly switch between an open and a closed state (i.e. regardless of conditions)?
K+ leak channels
164
K+ channels are the main ion channels open in a resting cell making the plasma membrane more permeable to what ion than any other ion?
K+
165
The movement of K+ out of the cell (down its concentration gradient) through the K+ leak channels transfers (+) charges outside of the cell. This leaves behind what? It generates what?
Unpaired (-) charges which generates the membrane potential (an electrical field).
166
What kind of cells where the electrical potential across the plasma membrane is due to the passive transport of potassium ions through K+ leak channels?
Animal cells
167
K+ leak channels makes the inside of the cell slightly more what than the outside?
Negative
168
What pump plays a small role in generating the membrane potential by pumping 3 sodium ions out for every 2 potassium ions it pumps in?
The Na+/K+ pump
169
Na+.K+ pump establishes a low intracellular Na+ concentration which is balanced by what?
A high K+ concentration
170
Where do the intracellular K+ ions go?
They move down their concentration gradient out of the cell
171
The loss of (+) charged ions leaves behind an unbalanced (-) charge generating what?
A charge difference across the membrane
172
K+ ions will move down their gradient through what until they are balanced by their attraction to the (-) charged interior?
Potassium leak channels
173
K+ ions will move down their gradient through potassium leak channel s until they are balanced by their attraction to the (-) charged interior. What happens next?
There is no net flow of ions across the membrane
174
The equilibrium state is also called what?
The resting membrane potential
175
What is the resting membrane potential in animal cells?
Between -20mV to -120mV
176
What type of Ion channel is A?
Voltage-gated
177
What type of Ion channel is B?
Ligand-gated (Extracellular Ligand)
178
What type of Ion channel is C?
Ligand-gated (Intracellular Ligand)
179
What type of Ion channel is D?
Mechanically gated
180
If potassium leak channel is in the closed state (A), the membrane potential is zero. Why?
The positive and negative charges balance exactly (zero net charge on each side)
181
If the potassium leak channel is in the closed state (A), the potassium leak channel has more of what inside?
Potassium
182
If the potassium leak channel is in the open state (B), what will happen to the the potassium ions?
K+ ions will move down their concentration gradient (i.e out of the cell) until the membrane potential exerts a counterbalancing force preventing further K+ movement.
183
What describes a condition in which the flow of (+) and (-) charged ion across a membrane is balanced such that no difference in charge accumulates?
The resting membrane potential
184
What is measured as a voltage difference across the membrane and in animal cells it ranges from -20mV to -200mV.
The membrane potential
185
Because the inside of the cells is more negative with respect to the outside of the cell (due to the K+ leak channels) membrane potentials are presented as what values?
Negative values
186
In animal cells the membrane potential is a reflection of the difference of K+ concentration across the membrane since at rest this is the what?
Primary ion moved
187
The bacterial K+ channel is composed of how many identical transmembrane subunits that are arranged with (-) charged amino acids positioned at both the entrance and exit to the pore.
Four
188
The bacterial K+ channel is composed of how many identical transmembrane subunits that are arranged with (-) charged amino acids positioned where?
At both the entrance and exit to the pore.
189
The bacterial K+ channel has (-) charged amino acids block the entry of what kind of ions?
(-) charged ions
190
Each subunit of the bacterial K+ channel contributes an alpha-helix and a loop domain to the pore region to form what?
The selectivity filter of the channel
191
(Bacterial K+ channel) What atoms of the polypeptide backbone within the loop interacts with the dehydrated K+ ions as they pass through in a single file?
The carbonyl oxygen atoms
192
What is this structure?
Bacterial K+ channel
193
(Bacterial K+ channel) What ion that has lost its bound water can enter the pore and interact with the carbonyl oxygens that line the pore?
K+ ion
194
The carbonyl oxygens are spaced to accommodate what?
A dehydrated K+ ion
195
The energy required to dehydrate a K+ ion is balanced by what?
The energy regained by the interaction of the ion with the carbonxyl oxygens
196
How does the carbonyl oxygens in the pore select the ion?
The spacing
197
What kind of ion is too small to interact with the oxygens and is therefore unable to compensate for the energy expense associated with the loss of water molecules required for its entry?
A sodium ion
198
Identify which ion is X? (Sodium or Potassium?)
Potassium
199
Identify which ion is Y? (Sodium or Potassium?)
Sodium
200
Which ion channel gate is open (A or B?)
B
201
Which ion channel gate is closed (A or B?)
A
202
Ion channel gating: the opening and closing of what?
The channel pore
203
Ion channel gating involves the movement of what that line the pore within the membrane?
The transmembrane helices
204
The movement of the transmembrane helices that line the pore either blocks or opens the pathway for what?
Ion movement
205
What kind of movement does the transmembrane helices move depending on the type of the channel?
Described as a tilting, rotating or bending of the transmembrane helices depending on the type of channel
206
Ion channels allow for the flux of ions across a membrane without the co-passage of what?
Water
207
Specialized channels exist in prokaryotes and eukaryotes that allow for the specific transport of water without the passage of what?
Ions
208
What are specialized channels exist in prokaryotes and eukaryotes that allow for the specific transport of water without the passage of ions?
Aquaporins
209
How is an aquaporin constructed?
It is formed from four homomeric subunits with each monomer containing a water conducting pore
210
What kind of molecules pass through aquaporins in a single file and follow the carbonyl oxygens that line the pore?
Water
211
Ions are unable to pass through the aquaporin because the pore diameter is too small for the passage of hydrated ions and the presence of hydrophobic amino acids on one face of the pore is not energetically favorable for the passage of what?
Dehydrated ions
212
Some aquaporins allow the passage of what?
Glycerol and small sugars
213
What are also known as "exchangers"
Antiporters
214
What is the number of potassium ions moved per ATP by the sodium-potassium pump?
Two
215
What is the transport process mediating solute movement against its concentration gradient?
Active transport
216
What cannot diffuse through a lipid bilayer due to charge and hydration?
Ions
217
What class of ATP-driven pump undergoes autophosphorylation?
P type
218
What is the direction of sodium movement by the sodium-potassium pump?
Out of the Cell
219
What is primarily responsible for generating the membrane potential in animal cells?
Potassium Leak Channels
220
The plasma membrane sodium-calcium exchanger is driven by the concentration of what ion?
Sodium
221
What is the most abundant intracellular cation?
Potassium
222
What is the narrowest part of an ion channel; determines which ions can pass?
Selectivity filter
223
What describes the difference in electrical charge across a membrane?
Membrane potential
224
What is the net driving force generated by solute concentration gradient and electrical gradient?
Electrochemical gradient
225
Their movement of solutes across a membrane requires a change in conformation
Carriers
226
What transport process is mediated by channel proteins; no energy input required?
Passive transport
227
What form a narrow hollow pore for the passage of watersoluble molecules across a membrane?
Channels
228
No net flow of ions across the plasma membrane
Resting membrane potential
229
What is the property controlling the opening and closing of an ion channel?
Gating
230
What inhibitor blocks potassium binding to the sodium potassium pump?
Ouabain
231
Animal cells spend one-third of their energy driving what pump?
Sodium Potassium ATPase
232
What is the bacterial 'equivalent' of the sodium-potassium pump?
Proton pump
233
What mediates the transport of a single solute across a membrane?
Uniporter
234
What is the direction of calcium movement by the sodium-calcium exchanger?
Out of the cell
235
What can rapidly diffuse across a lipid bilayer?
Oxygen
236
What are water channels?
Aquaporins
237
What is a co-transport mechanism in which the two solutes are moved in the same direction across a membrane?
Symporter
238
What is the transport process in which solutes are moved 'through' a cell; e.g. the movement of glucose across an epithelial cell?
Transcellular
239
What is the most abundant extracellular cation?
Sodium
240
The SR localized Ca2+ pump moves what number of calcium ions per ATP hydrolyzed?
Two
