Transport of Molecules Across Membranes

Question 1

What types of molecules are able to cross a pure lipid bilayer? By what mechanism do they cross?

Answer 1

• Gases & small polar / uncharged molecules
• Passive diffusion

Question 2

What types of molecules are NOT able to cross a pure lipid bilayer?

Answer 2

• Ions
• Charged molecules
• Large uncharged / polar molecules

Question 3

What TWO factors influence the movement of charged molecules across a membrane?

Answer 3

1. Concentration gradient (chemical)
2. Electrical Potential (voltage)

Question 4

What does the Electrochemical gradient determine?

Answer 4

The energetically favourable direction of movement of a molecule

Question 5

What equation gives the equilibrium potential for two solutions separated by a membrane that is permeable only for a given ion (X+/-)?

Answer 5

Nernst Equation

(don’t need to know the equation)

Question 6

TRUE OR FALSE:
When ΔG is negative, there is net movement of a molecule INTO the cell?

Answer 6

True

Question 7

What are the THREE broad classes of transport proteins?

Answer 7

1. ATP-powered Pumps
2. Transporters /Carriers
3. Ion Channels

Question 8

What type of transport do ATP-powered Pumps facilitate?

Answer 8

Active Transport

Question 9

What type of transport do Transporters / Carriers facilitate?

Answer 9

• Facilitated Diffusion
  OR
• Coupled Transport / Secondary Active Transport

Question 10

What type of transport do Ion Channels facilitate?

Answer 10

Facilitated Diffusion

Question 11

What are the THREE classes of ATP-powered Pumps?

Answer 11

1. P class
2. V class
3. ABC superfamily

Question 12

What are the THREE classes of Ion Channels?

Answer 12

1. Voltage gated
2. Ligand gated
3. Non-gated (resting)

Question 13

What are the THREE classes of Transporters / Carriers?

Answer 13

1. Uniporters
2. Symporters
3. Antiporters

Question 14

What reaction powers ATP-powered Pumps?

Answer 14

ATP hydrolysis
* ATP –> ADP + Pi

Question 15

TRUE OR FALSE:
ATP-powered Pumps transport molecules WITH their electrochemical gradient?

Answer 15

False.
They transport AGAINST the gradient

Question 16

What is Active Transport?

Answer 16

Coupling of ATP hydrolysis and “uphill” transport of ions or small molecules

Question 17

Does Active Transport provide high or low rates of transport?

Answer 17

Low

Question 18

What type of molecule do P-Class ATP-powered Pumps transport?

Answer 18

Ions

Question 19

What type of molecule do V-Class ATP-powered Pumps transport?

Answer 19

Protons

Question 20

Where in the cell are V-class pumps found?

Answer 20

Lysosomes and Vacuoles
* generate acidic compartments

Question 21

What type of molecules do ABC superfamily pumps transport?

Answer 21

• Ions
• Sugars
• Amino acids
• Phospholipids
• Peptides

Question 22

What are the domains of an ABC superfamily pump?

Answer 22

Two transmembrane and two ATP binding ‘core’ domains

Question 23

What does ‘ABC’ stand for in ABC superfamily pumps?

Answer 23

ATP Binding Cassette

Question 24

What is the structure of the P-class pump?

Answer 24

2x α and 2x β subunits

Question 25

What happens to the Ion during transport through a P-class pump?

Answer 25

**P**hosphorylated on a conserved Aspartate in α subunits | P for Phosphorylated and P-class

Question 26

What are TWO examples of P-class pumps?

Answer 26

1. Na+ / K+ ATPase - pumps K+ IN and Na+ OUT of cell 2. Ca++ ATPases in PM and ER - pump Ca++ OUT of cytosol

Question 27

What is the mechanism of action for Na+ / K+ ATPase?

Answer 27

Hydrolyis of **1 ATP** per cycle coupled to transport of **3 Na+** OUT of cell and **2 K+** INTO cell

Question 28

How many conformational states does Na+ / K+ ATPase have?

Answer 28

2 E1 & E2 * unidirectional transport

Question 29

What are the affinities for Na+ and K+ in the E1 state?

Answer 29

3 HIGH affinity Na+ and 2 LOW affinity K+ sites on Cytosolic side

Question 30

What are the affinities for Na+ and K+ in the E2 state?

Answer 30

3 LOW affinity Na+ and 2 HIGH affinity K+ sites on Extracellular side

Question 31

TRUE OR FALSE: V-class proton pumps run the in SAME direction as ATP Synthase?

Answer 31

False. They run in the OPPOSITE direction

Question 32

Where are the V0 and V1 components of a V-class proton pump located respectively?

Answer 32

* V0 located in MEMBRANE * V1 located in CYTOSOL

Question 33

Which subunits hydrolyse ATP to provide energy to pump protons across the membrane in V-class proton pumps?

Answer 33

β subunits of V1

Question 34

What is the pH of a Lysosome?

Answer 34

4.5 - 5

Question 35

What is the mechanism of action for V-class proton pumps to acidify intracellular compartments?

Answer 35

* Protons are charged (cations) so pumping protons in is electrogenic * Charge builds up across membrane to prevent acidification of compartment * Anions are transported in the same direction to counteract

Question 36

What are the domains of ABC superfamily pumps?

Answer 36

2x Transmembrane domains and 2x Cytosolic ATP-binding domains

Question 37

What protein is an example of an ABC superfamily pump?

Answer 37

Multi-drug resistance transport proteins (MDR1 & 2)

Question 38

Are MDR1 & 2 over or under expressed in tumours?

Answer 38

Overexpressed * higher concentration of drug required to kill tumour cells

Question 39

What mechanism does MDR1 & 2 use to transport molecules across the membrane?

Answer 39

Flippase

Question 40

What molecule does the Cystic Fibrosis Transmembrane Regulator (CFTR) transport?

Answer 40

Cl- ions

Question 41

Mutation of which ABC gene causes a rare disorder called Tangiers Disease?

Answer 41

ABC A1

Question 42

Mutation of which ABC gene causes X-linked Adrenoleukodystrophy (ALD)?

Answer 42

ABC D1