L8: Cell Membranes & Membrane Transport

Question 1

What barriers do biological membranes have?

Answer 1

Selective permeable

Question 2

What do the selective permeable biological membranes block?

Answer 2

Passage of almost all water soluble molecules

Question 3

What do charged polar molecules require to move across the membrane?

Answer 3

Specialist proteins (pumps, transporters etc.)

Question 4

What molecules can permeate across the lipid bilayer?

Answer 4

Hydrophobic molecules, small uncharged polar molecules

Question 5

Is the concentration of Na+ ions higher on the outside or inside of cells?

Answer 5

Outside

Question 6

Is the concentration of K+ ions higher on the inside or outside of the cell?

Answer 6

Inside

Question 7

Is the concentration of Cl- higher on the inside or outside of cells?

Answer 7

Outside

Question 8

Define Simple/Passive diffusion

Answer 8

A molecule dissolves in the phospholipid bilayer, diffuses across and moves along the concentration gradient

Question 9

What does the rate of diffusion depend on?

Answer 9

Octonal/water PARTITION COEFFICIENT (Kow) of the solute

Question 10

What is Kow? What does it tell us?

Answer 10

Equilibrium constant for partitioning of a molecule between oil (octanol) and water
- Tells us how lipid loving something is

Question 11

If the value of Kow is higher what does it mean in terms of lipid?

Answer 11

More lipid soluble it is

Question 12

What are transmembrane movement of ions & hydrophilic molecules mediated by?

Answer 12

Proteins

Question 13

2 ways solutes can cross biomembranes

Answer 13

1) Passive diffusion
2) Active transport

Question 14

Why are ion channels gated?

Answer 14

Enables the generation of action potential

Question 15

Why do facilitated diffusion involve a conformational change in selective carrier protein?

Answer 15

Allow molecule to pass through the membrane & be released on the other side

Question 16

Define uniport transport

Answer 16

1 molecule transported at a time

Question 17

Define symport transport

Answer 17

2 kinds of molecules move in the same direction

Question 18

Define antiport transport

Answer 18

2 kind of molecules moving in the opposite direction

Question 19

What is a coupled transport?

Answer 19

Type of secondary AT where the movement of 1 molecule/ion moving down its conc grad drives the movement of another molecule across membrane

Question 20

Which 2 transports are part of coupled transport?

Answer 20

Symport & antiport

Question 21

What is the transporter affinity for substrate given by?

Answer 21

Km

Question 22

What does primary active transport use?

Answer 22

ATP

Question 23

What does secondary active transport use?

Answer 23

An electrochemical gradient

Question 24

Define active transport

Answer 24

Movement of molecules against the concentration gradient, requiring energy

Question 25

Where does Na+/K+ ATPase function in?

Answer 25

Plasma membrane

Question 26

Where does Ca2+ - ATPase function in?

Answer 26

Plasma membrane/ ER/SR

Question 27

Steps of the functioning of Na+/K+ ATPase

Answer 27

1) Na+ binds to intracellular site 2) This triggers an AUTOPHOSPHORYLATION of the pump 3) Phosphorylation cause change, releasing Na+ to expose K+ binding site 4) Binding of K+ triggers dephosphorylation 5) Pump returns to normal & K+ is discharged to the inside

Question 28

What does phosphorylation cause?

Answer 28

A conformational change to release Na+ to the outside & exposes a K+ binding site

Question 29

What does binding of K+ trigger?

Answer 29

A dephosphorylation of the pump

Question 30

What happens after the K+ binding site is exposed?

Answer 30

Pump returns to original conformation & K+ is discharged into the interior of the cell

Question 31

What is Na+/K+ ATPase a drug target for?

Answer 31

Treatment of congestive heart failure

Question 32

What does the Na+/Ca2+ antiporter (NCX) do to allow cardiac relaxation to occur?

Answer 32

Removal of Ca2 from the cytosol

Question 33

Role of Oubain

Answer 33

Inhibits the Na+/K+ ATPase by preventing K+ from binding

Question 34

Action of Na+/K+ ATPase in the treatment of congestive heart failure Mention 1) Oubain 2) Intracellular Na+

Answer 34

1) Oubain inhibits Na+/K+ ATPase by preventing K+, decreasing rate of Na+ 2) This increases intracellular Na+, reducing NCX activity, resulting in slower Ca2+ efflux

Question 35

What is SGLUT 1 important for?

Answer 35

Intestinal epithelial cells for absorption of dietary glucose

Question 36

Why is SGLUT 2 important?

Answer 36

Epithelial cells in proximal tubules of kidney for reabsorption of glucose from primary urine

Question 37

Explain the glucose uptake by intestinal epithelial cells Mention: 1) SGLT1 as a symporter 2) Glucose leaving GLUT2 3) Na+/K+ pump

Answer 37

1) SGLT1 brings glucose & Na+ into the cell using energy from Na+ to drag glucose against gradient into cell 2) Glucose exits cell at basal membrane through GLUT2, allowing glucose to flow down its conc grad into bloodstream 3) Na+ level is low inside, Na+/K+ ATPase pump (using ATP) kicks Na+ out & bring K+ in

Question 38

What is the mechanism by which cholera toxin causes diarrhoea?

Answer 38

Activating CFTR to cause Cl- secretion

Question 39

Which transporter is most important for rehydration in oral rehydration therapy for cholera?

Answer 39

SGLUT1

Question 40

Is Na+ or K+ lower inside cells?

Answer 40

Na+