Question 1

Gated ion channels
(I)exist because active transporters cannot maintain the gradient at a rate equal to non- gated ion flow.
(II)remain open unless acted on by an external stimulus.
(III)remain open to all ions that are smaller than the pore diameter.
(IV)can transport varying ions.

Accepted Answer

Gated ion channels exist to allow cells to rapidly change their ion permeability in response to various stimuli, not because active transporters cannot maintain the gradient. They do not remain open unless acted on by an external stimulus; rather, they open or close in response to specific stimuli. They are selective for specific ions, not just any ion smaller than the pore diameter.

Question 2

ClC Cl^- channels (I)assist in transport by forming a strong electrical dipole with the N-terminal end positively charged. (II)effectively funnel ions into the pore via electrostatic interactions with basic amino acids. (III)have a selectivity filter constructed from the N-terminal ends of α-helices,whose dipoles attract Cl^-ions. (IV)rely on the side chain hydroxyl groups from Ser and Tyr.

Accepted Answer

The answer of ClC Cl^- channels (I)assist in transport by forming...

Question 3

In the intestinal epithelium,glucose enters the cell in symport with ______,which is subsequently ejected by ________.

Accepted Answer

Glucose enters the intestinal epithelial cell in symport with sodium ions (Na+) through the Na+/glucose cotransporter (SGLT1). These Na+ ions are subsequently ejected out of the cell by the Na+/K+ ATPase pump. This maintains the Na+ and K+ gradients required for various cell processes. Therefore, option C is the correct choice.

Question 4

The concentration of cytosolic Ca²⁺ is _________ the extracellular concentration of Ca²⁺.

Accepted Answer

The concentration of cytosolic Ca2+ is much less than the extracellular concentration of Ca2+. Typically, cells maintain a low intracellular calcium concentration, which is crucial for various cellular processes and signaling pathways.

Question 5

Which does not occur when neurons are stimulated?

Accepted Answer

During neuronal stimulation, Na^+ ions actually enter the cell, not exit, during local depolarization. This influx of Na^+ ions is what causes the depolarization.

Question 6

Which of the following is true about the (Na⁺-K⁺)-ATPase transporter?

Accepted Answer

The (Na⁺-K⁺)-ATPase transporter hydrolyzes ATP, not GTP, and involves phosphorylation of an aspartyl residue, not glutamyl. In the E2 state, phosphate hydrolysis releases potassium ions to the cytosol and rearranges the transporter back to the E1 state.

Question 7

A pore that simultaneously transports two different molecules in different directions is called

Accepted Answer

A pore that simultaneously transports two different molecules in opposite directions is called an antiport.

Question 8

Ouabain inhibits the (Na⁺-K⁺)-ATPase pump,resulting in

Accepted Answer

Ouabain inhibits the (Na⁺-K⁺)-ATPase pump, which leads to an increase in intracellular sodium. This indirectly increases intracellular calcium via the sodium-calcium exchanger, enhancing cardiac muscle contraction strength.

Question 9

Which of the following correctly rank the steps in erythrocyte glucose transport by GLUT1?
(I)Glucose binding results in a conformational change,opening the binding site on the opposite side of the membrane
(II)Glucose binds to the transporter on one side of the membrane
(III)The transporter reverts to initial conformation
(IV)The glucose disassociates

Accepted Answer

The correct sequence of steps in erythrocyte glucose transport by GLUT1 is as follows:
(I) Glucose binding results in a conformational change, opening the binding site on the opposite side of the membrane
(II) Glucose binds to the transporter on one side of the membrane
(IV) The glucose dissociates
(III) The transporter reverts to initial conformation. 
Option B is the only choice that lists the steps in the correct chronological order.

Question 10

The rapid transport of K⁺ ions by the KcsA ion channel moves up to ____ ions per ______.

Accepted Answer

The passage states that the rapid transport of K⁺ ions by the KcsA ion channel moves up to 10⁸ ions per second. Therefore, the correct answer is D.

Question 11

Vanilomycin

Accepted Answer

Vanilomycin is a cyclic polypeptide that functions as a K⁺ carrier, specifically transporting amino acids with a lysine (K), serine (S), and a phenylalanine (F) at positions 1, 1, and 10 within the peptide sequence.

Question 12

Which statement about aquaporins is false?

Accepted Answer

Aquaporins are specialized membrane proteins that facilitate the transport of water across cell membranes. They are highly selective for water molecules, excluding ions including hydronium ions (H3O+), which contradicts statement A. They achieve this selectivity through a narrow pore size and specific interactions within the pore, not by transporting hydronium ions efficiently.

Question 13

The Kv channel is transiently closed by ___________.

Accepted Answer

The Kv channel is transiently closed by a spherical globular segment on the N-terminus known as the ball and chain mechanism. This segment blocks the ion-selective pore of the channel and prevents ion flow until it is removed by a specific signal.

Question 14

Lactose permease uses a ___________ gradient generated ______ to cotransport lactose across the cell membrane.

Accepted Answer

Lactose permease uses a proton gradient generated via oxidative metabolism to cotransport lactose across the cell membrane.

Question 15

When the cardiac glycoside,digitoxin,is used for heart failure,the effects include: (I)inhibition of phosphate hydrolysis from E₂ of the (Na⁺-K⁺)-ATPase pump (II)activation of the (Na⁺-K⁺)-ATPase pump (III)increase in intracellular Na⁺ concentration (IV)increase in Ca²⁺ concentration in the sarcoplasmic reticulum

Accepted Answer

Digitoxin inhibits phosphate hydrolysis from the (Na+K+)-ATPase pump, leading to an increase in intracellular sodium and calcium concentrations. This increase in calcium concentration in the sarcoplasmic reticulum ultimately leads to increased contractility of the heart muscle. Therefore, choices I and II are both incorrect. Choice III is correct, as digitoxin increases intracellular Na+ concentration. Finally, choice IV is also correct, as digitoxin increases Ca2+ concentration in the sarcoplasmic reticulum. Therefore, the best option is B, which includes choices I, III, and IV.

Question 16

A graph of the rate of glucose transport via the GLUT1 transporter vs.glucose concentration would have a ________ shape indicating that higher glucose concentrations increase the rate of transport until all the sites are saturated.

Accepted Answer

The graph would have a hyperbolic shape because the rate of glucose transport increases with glucose concentration up to a point where all transporter sites are saturated, beyond which the rate no longer increases, reflecting the characteristics of Michaelis-Menten kinetics typical of many enzyme-catalyzed reactions, including transporter-mediated transport.

Question 17

Gap junctions

Accepted Answer

Gap junctions allow exchange of small molecules between cells within an organ. They generate a direct connection between the cytoplasm of adjacent cells, forming a channel that allows the passage of small molecules such as ions, second messengers, and metabolites. Gap junctions are critical for cell-to-cell communication, coordination of cellular activities, and maintenance of tissue homeostasis. However, gap junctions do not allow the passage of macromolecules.

Question 18

Which features allow the KcsA channel to selectively transport K⁺? (I)The entrance of the channel contains hydrophobic residues which forces the removal of waters of hydration. (II)It is attracted to the entrance of the channel via electrostatic interactions. (III)The "selectivity filter" involves a narrowing of the channel,allowing only dehydrated K⁺ access. (IV)As K⁺is transported through the channel it interacts with −C=O groups from the protein.

Accepted Answer

The KcsA channel selectively transports K+ ions due to electrostatic interactions at the entrance (II), the narrowing of the channel in the selectivity filter that allows only dehydrated K+ ions (III), and interactions with carbonyl groups (IV).

Question 19

In the body hydrogen ions produced from the reaction of carbonic anhydrase are transported into the lumen of the stomach via an ATP utilizing proton pump.The removal of hydrogen ions drives formation of bicarbonate ions and a concentration gradient is formed.Bicarbonate is transported out at the same time that chloride ions are transferred in.Based on this information,which of the following is FALSE?

Accepted Answer

The statement "The pump driving bicarbonate out and chloride in must require ATP directly" is false, as bicarbonate-chloride pump is an antiport system which uses the potential energy stored in the electrochemical gradient of chloride ions to drive the export of bicarbonate. Thus, it does not require ATP directly.

Question 20

Drug resistance is frequently traced to
(I)the MDR transporter.
(II)overexpression of P-glycoprotein.
(III)increased number of specific ABC transporters.
(IV)the evolution of selectivity filters.

Accepted Answer

Drug resistance is frequently traced to the MDR transporter, which is involved in exporting drugs out of cells. Overexpression of P-glycoprotein, which is an MDR transporter, can also lead to drug resistance. The increased number of specific ABC transporters is another mechanism that can contribute to drug resistance. The evolution of selectivity filters, however, is not a commonly identified mechanism behind drug resistance.

Quiz 10: Membrane Transport

Gated ion channels (I) exist because active transporters cannot maintain the gradient at a rate equal to non- gated ion flow. (II) remain open unless acted on by an external stimulus. (III) remain open to all ions that are smaller than the pore diameter. (IV) can transport varying ions.

In the intestinal epithelium,glucose enters the cell in symport with ,which is subsequently ejected by __.

The concentration of cytosolic Ca²⁺ is _________ the extracellular concentration of Ca²⁺.

Which does not occur when neurons are stimulated?

Which of the following is true about the (Na⁺-K⁺) -ATPase transporter?

A pore that simultaneously transports two different molecules in different directions is called

Ouabain inhibits the (Na⁺-K⁺) -ATPase pump,resulting in

The rapid transport of K⁺ ions by the KcsA ion channel moves up to ions per __.

Vanilomycin

Which statement about aquaporins is false?

The Kv channel is transiently closed by ___________.

Lactose permease uses a _____ gradient generated to cotransport lactose across the cell membrane.

A graph of the rate of glucose transport via the GLUT1 transporter vs.glucose concentration would have a ________ shape indicating that higher glucose concentrations increase the rate of transport until all the sites are saturated.

Gap junctions

Drug resistance is frequently traced to (I) the MDR transporter. (II) overexpression of P-glycoprotein. (III) increased number of specific ABC transporters. (IV) the evolution of selectivity filters.

Quiz 10: Membrane Transport

Gated ion channels (I) exist because active transporters cannot maintain the gradient at a rate equal to non- gated ion flow. (II) remain open unless acted on by an external stimulus. (III) remain open to all ions that are smaller than the pore diameter. (IV) can transport varying ions.

In the intestinal epithelium,glucose enters the cell in symport with ______,which is subsequently ejected by ________.

The concentration of cytosolic Ca2+ is _________ the extracellular concentration of Ca2+.

Which does not occur when neurons are stimulated?

Which of the following is true about the (Na+-K+) -ATPase transporter?

A pore that simultaneously transports two different molecules in different directions is called

Ouabain inhibits the (Na+-K+) -ATPase pump,resulting in

The rapid transport of K+ ions by the KcsA ion channel moves up to ____ ions per ______.

Vanilomycin

Which statement about aquaporins is false?

The Kv channel is transiently closed by ___________.

Lactose permease uses a ___________ gradient generated ______ to cotransport lactose across the cell membrane.

A graph of the rate of glucose transport via the GLUT1 transporter vs.glucose concentration would have a ________ shape indicating that higher glucose concentrations increase the rate of transport until all the sites are saturated.

Gap junctions

Drug resistance is frequently traced to (I) the MDR transporter. (II) overexpression of P-glycoprotein. (III) increased number of specific ABC transporters. (IV) the evolution of selectivity filters.

In the intestinal epithelium,glucose enters the cell in symport with ,which is subsequently ejected by __.

The concentration of cytosolic Ca²⁺ is _________ the extracellular concentration of Ca²⁺.

Which of the following is true about the (Na⁺-K⁺) -ATPase transporter?

Ouabain inhibits the (Na⁺-K⁺) -ATPase pump,resulting in

The rapid transport of K⁺ ions by the KcsA ion channel moves up to ions per __.

Lactose permease uses a _____ gradient generated to cotransport lactose across the cell membrane.