Transport Across Membranes

Question 1

Passive diffusion of polar molecules involves and requires what

Answer 1

Involves desolvation and thus has a high activation barrier

Question 2

How can transport across the membrane be facilitated for polar substances?

Answer 2

By proteins that provide an alternative diffusion path

Question 3

Transporters/Permeases are what?

Answer 3

Proteins that allow transport across the membrane especially polar solutes

Question 4

what are the 2 main classes of membrane transport proteins

Answer 4

Carriers and channels

Question 5

Name another 2 names for carriers

Answer 5

Permeases or transporters

Question 6

Permeases/Carriers transfer what

Answer 6

ions, sugars, amino acids and metabolites

Question 7

How doe carriers work?

Answer 7

Bind the specific solute to be transported and undergo a series of conformational changes to transfer the bound solute across

Question 8

Describe how channels work?

Answer 8

Form aqueous pores that extend acros the bilayer. When the pores are open, allow specific solutes, usually ions of appropriate size and charge to pass through.
They have a weak interaction with the solute.

Question 9

What are aquaporins?

Answer 9

The channels that transport water through the cell membrane

Question 10

What is osmosis

Answer 10

Osmosis is the spontaneous net movement of solvent molecules through a semi-permeable membrane into a region of higher solute concentration

Question 11

A hypotonic solution is what

Answer 11

There is less solute in the outside solution

Question 12

A hypertonic solution is what

Answer 12

There is more solute in the outside solution

Question 13

If a blood cell is in a hypotonic solution

1) what happens to the blood cell
2) why

Answer 13

1) The blood cell absorbs water and swells

2) There is more water outside the cell (less solute outside cell) so the blood cell absorbs this water

Question 14

If a blood cell is in a hypertonic solution

1) what happens to the blood cell
2) why

Answer 14

1) The blood cell loses water and shrinks

2) There is less water outside the blood cell (more solutes outside the blood cell) so the blood cell releases water

Question 15

What is the name of a red blood cell that is in a very hypotonic solution and has burst

Answer 15

Lysed

Question 16

What is the name of a red blood cell that is in a very hypertonic solution

Answer 16

Crenated

Question 17

Why do erythrocytes have a high density of aquaporins on their cell surface?

Answer 17

To allow water to flow at a fast rate

Question 18

Facilitated diffusion/Passive transport is mediated by what 2 proteins

Answer 18

Channels and carrier

Question 19

Active transport which requires energy is driven by?

Answer 19

ATP hydrolysis, ion gradients and light

Question 20

Movement of solutes across a permeable membrane is what

Answer 20

Simple diffusion down an electrochemical gradient

Question 21

What is the rate limiting step in terms of movement of things across the membrane

Answer 21

Movement across the hydrophobic portion of the membrane is the rate limiting step

Question 22

What accompanies passage of hydrophilic solutes through lipid bilayer of a biological membrane

Answer 22

Energy changes because polar solutes need diff paths to cross membranes