Chapter 8: Transport Across a Membrane

Because the procedure you are using to modify plants requires their cell membranes to be pulled away from the cell walls by plasmolysis, you place the cells in a(n)

hypertonic solution

ABC-type ATPAse that inhibit the effectiveness of anti-tumor drugs by transporting the drugs out of tumor cells are known as

multi-drug resistance (MDR) transporters.

Each of the following is an example of facilitated diffusion except - glucose transport by GLUT1. - chloride-bicarbonate exchange. - aquaporin transport. - ion channel transport. - oxygen transport.

oxygen transport

Transmembrane movement of a substance down a concentration gradient by a membrane protein is called ________.

passive transport/ facilitated diffusion

Osmosis requires a ________ membrane that is ________ to solute molecules and permeable to water molecules.

semipermeable; impermeable

Matching: transports water across membranes

simple diffusion and facilitated diffusion

In carrier protein function kinetics, Km is the

solute concentration at which the transport rate is half maximal.

When Peter Agre and colleagues compared frog oocytes expressing aquaporin with control coccyges lacking aquaporin placed in pure water, they found that

the oocytes expressing aquaporin swelled and burst as water was transported into the cells.

What specific type of P-type ATPase pumps H+ to acidify the stomach and is inhibited by proton pump inhibitor drugs used to treat excess stomach acid?

type 2

What type of P-type ATPase would you expect to find is defective in a novel cell line in which you observe that maintenance of the phospholipid asymmetry in the plasma membrane is impaired?

type 4

Water moves across the plasma membrane into or out of a cell by osmosis when

water diffuses through a semipermeable membrane toward a higher solute concentrations

Phosphorylation of glucose following its transport into a cell

increases glucose transport into the cell by increasing its concentration gradient across the plasma membrane

Matching: driven by an ion gradient

indirect active transport

When erythrocytes are in the capillaries of body tissues, CO2 diffuses ________ and is converted to ________.

inward; bicarbonate

When erythrocytes are in the capillaries of the lungs, O2 diffuses ________ and is bound to ________.

inward; hemoglobin

Different ABC transporters can transport

ions, sugars, amino acids, peptides, and polysaccharides

All of the following are true about a partition coefficient except

it is the concentration at which the rate of transport is half maximal.

The primary difference between active transport and facilitated diffusion is that active transport is the only one of the two in which

the direction of transport is [S]low → [S]high

Matching: Na+/K+ ATpase pump

active transport

Matching: requires direct ATP hydrolysis

active transport

Matching: transports ions up concentration gradients

active transport

Matching: transporters glucose across membranes

active transport and indirect active transport

Transmembrane movement of a substance up a concentration gradient requires ________ transport.

active

One way in which ions are specifically transported into the cell is via

gated channels

Each of the following molecules move across membranes by simple diffusion except - oxygen - fatty acids - water -glucose - carbon dioxide

glucose

Ion gradients established across membranes by V-tpye ATPase pumps range from

10-10,000-fold

The Na+/K+ ATPase pump actively moves

3 Na+ out, 2 K+ in

Binding and hydrolysis of ATP in a "cassette" domain is part of the transport mechanism of what types of transporters?

ABC type

Which of the following is a characteristic of facilitated diffusion (passive transport) of a molecule across a membrane? - Its rate is higher than that of simple diffusion of the molecule. - It is highly specific for the molecule being transported. - The direction of transport is determined by concentration and/or electrochemical gradients. - The rate of transport is saturable. - All of the above are true.

All above are true

Active transport makes it possible for cells to - take up nutrients from the environment against concentrations gradients. - transport out secretory products and waste material against concentration gradients. - maintain non equilibrium intracellular concentrations of ions such as Na+, K+, Ca2+, and H+. - establish an electrical potential across the membrane. - All of the above are correct.

All of the above are correct

What is true about the mechanism of the 2Na+/glucose symporter?

Binding of 2 Na+ to the symporter on the inside of the cell causes the symporter to open to the outside of the cell and release of the Na+ ions.

Cystic fibrosis is the result of a malfunction of a cellular ABC transporter that transports

Cl-

Exergonic flow of protons through the ________ type of transport generates ATP in bacteria, mitochondria, and chloroplasts.

F

What glucose transporters has properties that facilitate glucose transport out of human liver cells to maintain blood sugar level homeostasis?

GLUT 2

What is an example of indirect active transport

Na+/glucose symport

Mutations in bacterial porins typically lead to antibiotic resistance by

blocking diffusion of the antibiotic through the porin channel.

Bacterial porins transport

hydrophilic molecules smaller than 600 Da.

Uptake of food particles by trapping them within an invagination of the plasma membrane is called ________.

endocytosis

Matching: requires ligand binding and therefore Km for transport can be calculated

facilitated diffusion and active transport

Consider a nerve cell with an internal Cl- concentration of 50 mM, a membrane potential of 60 mV and an external Cl- concentration of 100 mM. Each of the following is true for Cl- import into the cell except - import is down a concentration gradient. - import is down an electrochemical concentration gradient. - import ΔG is positive. - import requires energy input. - All are true.

import is down an electrochemical concentration gradient

Matching: Na+/glucose symport

indirect active transport

Although all P-type ATPAse use the energy of ATP hydrolysis to transport solutes they differ in which of the following? - structure - mechanism - localization in cells - physiological roles - All of the above are correct

All of the above are correct

Which of the following types of transport occur across the erythrocyte membrane? - O2 and CO2 passive diffusion - aquaporin water transport - Cl- bicarbonate ion antiport - glucose uniport - All of the above are correct

All of the above are correct

Based on the same graph, transport of substances B and C - exhibits saturation kinetics. - involves transporter proteins. - is not directly dependent on the B and C permeability coefficients. - is likely faster than simple diffusion. - All of the above are correct.

All of the above is correct

Each of the following is true for the mechanism of the Na+/K+ ATPase pump except - the E2 conformation is open to the outside of the cell and has high affinity for K+. - the E1 conformation is open to the inside of the cell and has high affinity for Na+. - Na+ triggered phosphorylation of the pump stabilizes the E2 conformation. - K+ triggered dephospho rylation of the pump stabilizes the E2 conformation. - Each E1-E2 cycle pumps 3 Na+ ions out and 2 K+ ions in.

K+ triggered dephospho rylation of the pump stabilizes the E2 conformation

Urea is a small molecule that is transported out of most cells by passive diffusion, but some cells, including kidney cells, have urea-facilitated transporters. Given an assay to measure the amount of urea on one side of the cell plasma, design an experiment to distinguish which mechanism an uncharacterized cell you have isolated uses to transport urea. Include graphs, if this aids in your discussion.

Measure and graph the initial rate of urea transport over a range of urea concentrations. If the rate exhibits saturation kinetics at higher urea concentrations, transport is mediated by a urea transport protein. (To distinguish whether this is facilitated or active transport, it may be necessary to determine whether the urea is transported back out when the external concentration is lowered.) If the import rate increases linearly even at high urea concentrations and does not saturate, the urea transport is by passive diffusion.

What type of ATPase pump is sensitive to vanadate (which inhibits phosphorylation of the pump during its activity mechanism)?

P type

The type of transport ATPase that is reversibly phosphorylated as part of the transport mechanism is the ________ ATPase.

P-type

What is the mechanism by which expression of an MDR protein affects treatment of cancer cells with an antitumor drug? How might you potentially counter the effect of such transporters?

The MDR ABC-type ATPase exports the drug, thereby detoxifying the cell, before the drug can inhibit the cancer cell activity. Countering the effect of MDR would require inhibiting its activity while treating with the antitumor drug. MDR activity might be inhibited with a specific chemical inhibitor or an inactivating antibody. Other approaches might involve knocking down MDR expression with molecular approaches involving gene knockouts or inhibiting RNAs.

Explain why the steroid hormone estradiol (MW 272) readily crosses membranes by simple diffusion but the much smaller H+ requires transport proteins.

The nonpolar molecule estradiol has a higher partition coefficient, because it can much more readily dissolve in and diffuse across the hydrophobic phase of a membrane. Any charged molecule, even one as small as H+, forms a shell of hydration, which would require an input of energy to dissolve in the lipid bilayer. A H+ protein transporter circumvents this problem by screening the H+ from the hydrophobic phase of the membrane during transport.

Why would some cells, such as erythrocytes, express GLUT1, but other cells, such as liver cells, express GLUT2, which has a different kinetic relationship between v (rate of diffusion) and Δ[S] (solute concentration gradient)?

The v vs [S] kinetic relationship for GLUT1 enables it to efficiently import glucose from the bloodstream into the cell to use for cellular activities but not to export glucose. The v vs [S] kinetic relationship for GLUT2 enables it to import glucose into liver cells for storage when blood sugar concentration is high and to export glucose through the same transporter when blood sugar level drops to maintain blood sugar level homeostasis in the range of 3.6-5.0 mM.

The graph below shows the concentrations of B and C inside the cell over time when the cell that has imported B and C in Figure 8.1 above is transferred to a solution containing a much lower concentration of B and C. Based on these data and coupled with the data observed above, substance C is transported via (C is a straight line on the graph)

active transport

Whereas animal cells drive indirect transport with a Na_ gradient, most other organisms use

an H+ gradient

Most cells have a negative plasma membrane potential (Vm) because they have

an excess of negatively charged solute molecules inside the cell.

The transport of two molecules across the cell membrane in different directions by one transporter is called ________.

antiport

What protein types would you predict is defective in kidney water balance disorders?

aquaporin

Each of the following is a characteristic of active transport mechanisms except - sensitivity to inhibitors such as proton pump inhibitors. - non directionality for moving a solute in either direction across a membrane depending on the solute concentration gradient. - coupling transport of a solute down its concentration with transport of another solute up its concentration gradient via a symport or anti port mechanism.. - moving solutes away from equilibrium across a membrane. - coupling a thermodynamically unfavorable (endergonic) process with a favorable (exergonic) process.

non directionality for moving a solute in either direction across a membrane depending on the solute concentration gradient.

Gated-ion channels include each of the following expect - voltage-gates channels - ligand-gated channels - mechanosensitive channels - patch clamp-gated channels - All of the above are types of gated channels

patch clamp-gated channels

All of the following are active transporters except - symporters. - P-class pumps. - permeases. - bacteriorhodopsin. - ABC transporters.

permeases

The outer membranes of bacteria, mitochondria, and chloroplasts contain large nonselective channels made of multipass proteins known as ________ in which the transmembrane segment of the protein is composed of a ________.

porins; β-barrel

The energy necessary to drive the bacteriorhodopsin in proton pump that causes the proton gradient needed for ATP synthesis is generated by

retinal absorption of light energy

Matching: depends on high partition coefficient of the solute

simple diffusion

Matching: transports small, non polar molecules

simple diffusion

The graph above shows the initial rate of transport for each substance when the cells are placed in solutions of different concentrations of A, B, and C. Based on these data, substance A is transported via (A is a linear line)

simple diffusion

Transmembrane movement of a substance down a concentration gradient with no involvement of membrane proteins is called ________.

simple diffusion

Matching: direction of transport depends on the concentration gradient

simple diffusion and facilitated diffusion

Simultaneous transport of two molecules across the cell membrane in the same direction by one transporter is called ________.

symport

Frog oocytes are a useful experimental system for studying transporters, because a frog coccyges possess all the characteristics except - they are large, easily injected cells. - they express all transporters known. - they express injected heterologous mRNAs. - they are relatively inexpensive and easy to obtain. - they can be maintained in little more than pure water.

they express all transporters known

The erythrocyte anion exchange protein "ping-pong" transport mechanism involves

unidirectional transport of Cl- only out of the cell.

Consider an erythrocyte with an internal glucose concentration of 0.1 mM and an external glucose concentration of 5 mM. Each of the following is true about GLUT1 transport of glucose across the plasma membrane into the cell except - Keq is always equal to 1. - ΔG depends on the concentration gradient. - inward movement is exergonic. - ΔG° is always equal to 0. - the rate of GLUT1 transport is faster than that of simple diffusion.

ΔG depends on the concentration gradient

Knowing the ion concentration on both sides of the plasma membrane makes it possible to calculate the membrane potential (Vm), because at equilibrium

ΔG is 0