04_Membrane Transport

Question 1

What molecules can diffuse freely through the membrane?

Answer 1

Hydrophobic molecules (O2, CO2, N2, steroid hormones)

Question 2

Compare the diffusion of uncharged polar molecules and ions through the lipid bilayer.

Answer 2

Small uncharged polar molecules > large uncharged polar molecules > ions

**ions CANNOT diffuse freely through membrane.

Question 3

What does the ∆G during diffusion depend on for nonelectrolytes and electrolytes?

Answer 3

non-electrolytes: concentration (chemical) gradient

electrolytes concentration & voltage (electrochemical) gradient

Question 4

How are protein pores used for transport?

Answer 4

Used as ion channels (typically votage-gated)

PASSIVE transport

Question 5

What form of transport is the glucose transporter used for? How is the subsequent exit of glucose prevented?

Answer 5

Facilitated diffusion

Once inside the cell, glucose is phosphorylated.

Question 6

What are some key features that set facilitated diffusion apart from diffusion (apart from the involvement of a transporter)?

Answer 6

Facilitated diffusion is specific, it is saturable (reaches a max rate of solute movement), and is regulated.
Simple diffusion is not (on a all counts).

Question 7

How do primary pumps function? What do they typically transport?

Answer 7

hydrolyze ATP to move IONS against their concentration gradient.

Question 8

Which type of primary pump is found in all cell types? What does it typically transport?

Answer 8

P-type pymp
transports ions (Na+, K+, Ca2+, H+)

Question 9

Which types of primary pumps can create proton gradients?

Answer 9

V-type and F-type

and also P-type

Question 10

Which type of primary pump is composed of a dimer? What does it usually transport (general category)?

Answer 10

ABC transporter

transports small lipophilic molecules

Question 11

How do P-type pumps achieve necessary conformational ∆ for functioning?

Answer 11

phosphorylation

Question 12

Why is Ca+ a good signalling ion?

Answer 12

The ionic gradient is MUCH greater outside the cell compared to the cytosol; therefore, a small ∆ can be detected.

Question 13

In which organelles is Ca+ very abundant?

Answer 13

mitochondria and ER

Question 14

What type of pumps are found in membranes vesicles, vacuoles and lysosomes?

Answer 14

V-type pumps

Question 15

Apart from the ions they transport, what is a main difference between P- and V-type pumps?

Answer 15

P-type pumps are phosphorylated. In V-type pumps, the phosphate from ATP hydrolysis is not transferred to the pump.

Question 16

Which type of pumps can be made to “run backwards”? What does this mean?

Answer 16

F-type pumps

running backwards results in production of ATP from an existing ion gradient

Question 17

What are flippases? Which type of primary pumps can act as flippases?

Answer 17

Flippases move lipids in the bilayer from one leaflet to the other (flip-flop movement).
ABC transporters can function as flippases.

Question 18

How do Na+/K+ pumps function? What type of pump are they?

Answer 18

P-type primary pumps

They move Na+ and K+ against their concentation gradients.
E1 conformation: 3 Na+ bind in cytosolic side; ATP hydrolysis & phosphorylation of pump –> conformation change to E2.
3Na+ released into extracellular space. 2K+ bind
–> conformation change to E1, 2K+ released into cytosol.
SUMMARY: 3Na+ out, 2K+in

Question 19

What is ATP used for in secondary active transport?

Answer 19

ATP is used to create concentration gradient for one molecule, that will be then used to drive transport for OTHER molecules.

Question 20

Describe the movement of the molecule being transported with relation to the driving ion in symport and antiport.

Answer 20

Symport: driving ion moves down its concentration gradient in the SAME direction that the specific molecule is moving AGAINST its concentration gradient.

Antiport: specific molecule moves against its concentration gradient in the OPPOSITE direction of the driving ion moving DOWN its concentration gradient.