Cell membrane transport

Question 1

What are 2 types of passive transport?

Answer 1

Simple + facilitated diffusion

Question 2

What are 2 types of active transport?

Answer 2

Primary (direct) + secondary (indirect)

Question 3

What is the purpose of an electrochemical gradient?

Answer 3

Drives passive transport

Question 4

What is an electrochemical gradient dependent on?

Answer 4

Always dependent on conc. grad. of the solute. For charged molecules, also dependent on any difference in voltage between ICF and ECF

Question 5

What is simple diffusion?

Answer 5

Movement of an uncharged solute through lipid bilayer

Question 6

What does the speed of simple diffusion depend on?

Answer 6

• permeability of membrane to solute
• difference in con. between ECF and ICF

Question 7

What type of solute does simple diffusion allow to move?

Answer 7

Hydrophobic solutes

Question 8

What type of solutes do transmembrane proteins allow to move?

Answer 8

Hydrophilic solutes

Question 9

What are transmembrane proteins composed of?

Answer 9

Membrane-spanning alpha-helical domains

Question 10

What is a proteins membrane topology?

Answer 10

How the protein moves in + out of the membrane

Question 11

What are the types of transmembrane protein?

Answer 11

Pore, channel, carrier, pump

Question 12

How does a pore act as a transmembrane protein?

Answer 12

Form a channel but has not gate on it

Question 13

How does a channel act as a transmembrane protein?

Answer 13

Is a gated pore - can open and close for substances to move through

Question 14

How does a carrier act as a transmembrane protein?

Answer 14

It doesn’t have a clear opening, so substances bind to it

Question 15

How does a pump act as a transmembrane protein?

Answer 15

Requires ATP to change shape for transport

Question 16

How do transmembrane proteins allow substances to move across?

Answer 16

Create hydrophilic permeation pathways through the membrane

Question 17

What is special about the amino acid sequence of transmembrane proteins?

Answer 17

Amphipathic helices - alternating hydrophobic and hydrophilic amino acids as determined by their variable regions

Question 18

Which way do the hydrophobic + hydrophilic surfaces of the transmembrane protein face?

Answer 18

Hydrophobic-lipid membrane (outside)
Hydrophilic-creates central pore (inside)

Question 19

Describe pores

Answer 19

-allow for facilitated diffusion
-driving force for movement=electrochemical gradient
-always open
-made up of multiple subunits

Question 20

Describe channels

Answer 20

-allow for facilitated diffusion
-driving force for movement=electrochemical gradient
-gated ion channels
-made up of multiple subunits

Question 21

What does each channel have?

Answer 21

-a moveable gate
-a sensor
-a selectivity filter
-an open channel pore

Question 21

What are the types of sensors found in a channel?

Answer 21

-voltage
-ligand
-mechanical (membrane stretches so channel opens)

Question 21

Describe carriers

Answer 21

-allow facilitated diffusion
-driving force for movement=electrochemical gradient
-never has a continuous transmembrane path

Question 22

How do carriers work?

Answer 22

-the molecule enters the carrier through the outer gate + binds at the binding site
-outer gate closes + inner gate opens
-molecule exits + enters cell
-inner gate closes

Question 22

Is carrier mediated facilitated diffusion faster or slower?

Answer 22

Slower

Question 23

What limits carrier mediated facilitated diffusion?

Answer 23

-can become saturated -limited by number of carriers in membrane -limited by the speed by which carrier cycles through steps

Question 24

Describe active transport

Answer 24

-moves solutes against its electrochemical gradient -requires metabolic energy -uses ATP

Question 25

What are the 2 types of active transport?

Answer 25

Primary and secondary

Question 26

Describe primary active transport

Answer 26

-uses a pump -driving force is a chemical reaction e.g ATP hydrolysis into ADP

Question 26

Describe secondary active transport

Answer 26

-uses cotransporters + exchangers -uses electrochemical gradient from primary step -driving force=coupling the uphill movement of 1 solute with the downhill movement of another

Question 27

What else can carriers mediate?

Answer 27

-pumps -cotransporters -exchangers

Question 28

Describe the sodium potassium ATPase pump

Answer 28

-pump moves sodium out of cell + potassium into it -breakdown of ATP drives their movement in opposite directions -pumps can become saturated

Question 29

Describe cotransporters (symporters)

Answer 29

-move solutes in the same direction -secondary active transport -requires a driving solute whose electrochemical gradient provides energy (usually inward Na+)

Question 30

Describe exchangers (antiporters)

Answer 30

-move solutes in opposite directions -requires a driving solute whose electrochemical gradient provides energy (usually inward Na+)

Question 31

Which transmembrane protein has the slowest rate of transport?

Answer 31

Carrier