Membrane Transport

Question 1

Give 5 reasons why transport across the plasma membrane is needed,

Answer 1

1) To regulate the cell volume.
2) To maintain the cell pH.
3) To generate and maintain ionic concentrations
4) To remove toxins

Question 2

What is the model for diffusion in the plasma membrane called?

Answer 2

It is called the “Fluid-Mosaic Model”

Question 3

What is the 1st Law of Thermodynamics?

Answer 3

The Law of Conservation of Energy.

The law states that energy can be created or destroyed; it can only be redistributed or changed from one form to another.

Question 4

What is the 2nd Law of Thermodynamics?

Answer 4

The second law states that the entropy (disorder) of any isolated system, not in thermal equilibrium, will always increase.

Question 5

What is the difference between primary active transport and secondary active transport?

Answer 5

Primary active transport is ATP dependent and secondary active transport is dependent on energy from proton gradients.

Question 6

What is the basic difference between simple diffusion of facilitated diffusion?

Answer 6

In simple diffusion, molecules move down their concentration gradients but in facilitated diffusion molecules move against the concentration gradient.

Question 7

What are transporter proteins?

Answer 7

They are integral transmembrane proteins that lower the energy required for molecules to traverse the membrane.

Question 8

Which segments (S1-S6) of an ion channel together form the voltage gate and the transmembrane pore?

Answer 8

The hydrophobic segments S1-S4 form a voltage gate.

The segments S5 and S6 form the transmembrane pore.

Question 9

What gives ion channels their specificity to a particular ion?

Answer 9

The size of the ion and the coordination of their water shell

Question 10

Name two transporters that use ATP to directly move substances across a membrane and name what substance they transport.

Answer 10

ABC transporters and P-type transporters.

Question 11

How many domains does a typical ABC transporter have, and which domain allows for substrate specificity?

Answer 11

A typical SCB transporter is made from 4 domains.

The α-helical domain allows for substrate specificity.

Question 12

What is the difference between eukaryotic and prokaryotic ABC transporters?

Answer 12

Eukaryotic ABC transporters only export from a cell.

Prokaryotic ABC transports both import and export from a cell.

Question 13

What is one use of ABC transporters in bacteria?

Answer 13

Bacteria can use ABC transports to resist antibiotics.

Question 14

What is the P-glycoprotein and where is it predominantly found?

Answer 14

It is a protein that functions to pump foreign substances (e.g. phosphatidylcholine) out of cells.

It is found in high concentrations in the blood vessels of the brain, and in the cells that are involved in digestion.

Question 15

What is a Flippase and give an example of a flippase.

Answer 15

A flippase is a transporter that moves amphipathic molecules from the exoplasmic face to the cytosolic face.

P-glycoprotein (also known as MDR1) is an example of a flippase.

Question 16

What is the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR)?

Answer 16

It is a transporter found in the epithelial cells of the liver and lungs that mediates the passive diffusion of Cl- and HCO3-

Question 17

What does the CFTR channel require to open?

Answer 17

The CFTR channels requires both phosphorylation and ATP binding to open.

Question 18

Which domain in P-type transporters is the phosphorylation domain and ATP nucleotide binding domain?

Answer 18

P domain = phosphorylation domain.

N domain = ATP nucleotide binding domain.

Question 19

Give three examples of P-type transporters.

Answer 19

Ca2+ transporters, Na+/K+ transporters and H+/K+ transporters.

Question 20

What is the function of Na+/K+ transporters?

Answer 20

Na+/K+ transporters function to maintain the Na+ and K+ concentration differences in nerve cells by using one molecule of ATP to pump 2 K+ into the cell for every 3 Na+ pumped out

Question 21

What is the typical charge across a membrane?

Answer 21

The exterior of a membrane is more positive than the interior.

Question 22

Name an example of a Secondary Active transporter and what it transports.

Answer 22

Lactose permease is an example.

It uses a proton gradient to pump lactose and other sugars across membrane.

Question 23

What is the mechanism of transport of Lactose Permease?

Answer 23

1. A proton will bind to Glu-269 (Helix VIII) and Arg302.
2. Lactose will also bind to Arg-144 (Helix V and Glutamate-126 (Helix IV).
3. The binding of both the proton an lactose will result in a conformational change that will allow for the release of lactose in to the cell, and the release of the proton.

Question 24

What can the energy associated with molecule transport be defined as?

Answer 24

ΔG = RT x In ([X]b/[X]a) + Zx FΔΨ