Membrane Transport

Question 1

Definition of selective permeability

Answer 1

Only specific molecules can pass freely through the membrane

Question 2

Definition of passive diffusion

Answer 2

Down conc grad, across membrane, passive until equilibrium reached

Question 3

Definition of the partition coefficient

Answer 3

The rate at which the solute equilibrates

The more hydrophobic, greater the PC, the greater the rate of equilibration

Question 4

Definition of facilitated diffusion

Answer 4

Down conc grad, through membrane channel proteins

Passive until equilibrium reached

Question 5

Definition of gated ion channels

Answer 5

Ion channels allow facilitated diffusion selective for different ions

Question 6

Definition of active transport

Answer 6

Solutes move against conc grad w membrane protein, ATP hydrolysis

Question 7

Definition of primary active transport

Answer 7

ATP hydrolysis directly causes solute movement

Question 8

Definition of uniport

Answer 8

Transport of 1 solute

Question 9

Definition of symport

Answer 9

Transport of 2 solutes, same direction

Question 10

Definition of antiport

Answer 10

Transport of 2 solutes, different directions

Question 11

Definition of secondary active transport

Answer 11

ATP hydrolysis does not directly cause solute movement

Question 12

What is permeable through the plasma membrane

Answer 12

Hydrophobic molecules

Small uncharged polar

Question 13

Transport mechanisms

Answer 13

Simple diffusion
Facilitated diffusion
Gated ion channels
Primary active transport
Secondary active transport

Question 14

Simple diffusion

Answer 14

Down conc grad until equilibrium reached
Rate depends on partition coefficient of solute
More hydrophobic, greater PC, equilibrate more quickly

Question 15

Facilitated diffusion

Answer 15

Down conc grad until equilibrium reached

Requires channel protein

Question 16

Kinetics of transport with simple and facilitated diffusion

Answer 16

As [S] increases, J increases in simple diffusion
As [S] increases, J increases more steeply initially, plates out in facilitated diffusion
1/2Jmax = Km

Question 17

Tranporter affinity in diffusion

Answer 17

Low Km = High affinity

Question 18

Types of glucose transporter

Answer 18

GLUT 1
GLUT 2
GLUT 3
GLUT 4
SGLUT

Question 19

Location of GLUT 1

Answer 19

Everywhere, abundant in RBC

Low in skeletal muscle

Question 20

Function of GLUT 1

Answer 20

Low Km, mediates constitutive glucose uptake in tissue

Question 21

Location of GLUT 2

Answer 21

Liver, pancreas b cells

Question 22

Function of GLUT 2

Answer 22

High Km, high Jmax

Transports glucose => hepatocytes and beta cells when [blood glucose] increases

Question 23

Location of GLUT 3

Answer 23

Neurones

Question 24

Function of GLUT 3

Answer 24

Low Km

Question 25

Location of GLUT 4

Answer 25

Muscle, adipocytes

Question 26

Function of GLUT 4

Answer 26

Km=5mM, similar to fed state [blood glucose] | Insulin regulated, can change glucose uptake ability

Question 27

Insulin stimulated uptake of glucose

Answer 27

Stimulates glucose uptake in muscle, adipose, increase GLUT 4 in membrane GLUT 4 on membranous vesicles in cytoplasm Insulin binds to receptors, triggers movement of vesicles to membrane, merge, increase no on surface Increase in GLUT4 in membrane, increase uptake of glucose into cell

Question 28

Gated ion channels

Answer 28

Allow facilitated diffusion selective for different ions | Open/close in response to stimuli

Question 29

Types of gated ion channels

Answer 29

Ligand gated | Voltage gated

Question 30

Active transport

Answer 30

Up conc grad, w membrane protein | ATP hydrolysis

Question 31

Conc of Na+ in and out of cell

Answer 31

12mM | 145mM

Question 32

Conc of K+ in and out of cell

Answer 32

140mM | 4mM

Question 33

Na+/K+ pump

Answer 33

Phosphorylation at cytoplasmic side with ATP = conformational change Cytoplasmic end closes, external end opens Pump binds 2K+ and releases 3Na+ Hydrolysis of Pi closes external end, opens cytoplasmic end Release 2K+ into cell

Question 34

Structure of the Na+/K+ pump

Answer 34

a2b2

Question 35

Cotransoprt systems

Answer 35

Preestablished gradient used to drive transport of solute across membrane against gradient ATP hydrolysis used to establish primary gradient

Question 36

SGLUT cotrasnporter

Answer 36

Glucose absorption from intestine against gradient Symport Na+ gradient established by Na+/K+ pump, ATP hydrolysis drives glucose uptake Secondary AT

Question 37

Na+/Ca2+ cotransporter

Answer 37

Ca2+ export from muscle cells against gradient Na+/Ca2+ cotransporter=antiport Na+ gradient established by Na+/K+ pump and ATP hydrolysis used to drive CA2+ export from cells Secondary AT

Question 38

Secretion of insulin by B cells

Answer 38

Glucose =FD=> GLUT2 (b cells) Glucose =metabolised=> ATP Increase in ATP/ADP ration ==> closure of cell surface K ATP channels ==> cell membrane depolarisation Voltage gated Ca2+ channels open, increase IC Ca2+ Increase Ca2+ ==>< exocytosis of insulin in vesicles