exam 2: lecture 5

Question 1

ion channel diffusion

Answer 1

allow ions( small charged molecules) to diffuse across the membrane
-there are electrochemical gradients across membranes

-gramicidin: channel
an antibiotic that is used to break down the ion gradients in bacteria and kill them (with hydrophilic interior & hydrophobic exterior)
(Na+, K+, Cl-)
permeable to everything: no selectivity

valinomycin: carrier

Question 2

mechanism of action of a channel-forming ionophore

Answer 2

hydrophilic portion is made up of aa (spiral in shape)
needs 2 channels to transport ions across (homodimer)
-serves as a conduit for ions-> making membrane leaky + discharging ion gradients

Question 3

what does gramicidin do to electric currents?

Answer 3

the antibiotic increases electric currents (ion flow across membrane)

Question 4

what is an example of an ion channel?

Answer 4

CFTR
Cl- moves up duct to from sweat-> Na+ follows along the electrochemical gradient (making sweat less salty)

Question 5

facilitated carrier diffusion 1

Answer 5

ion carriers-facilitate diffusion
1. valinomycin ( membrane protein) faces the outside of the cell with its binding site
2. an ion from outside binds
3. protein-ion complex diffuses across the membrane
4. ion is released into the interior of the cell

Question 6

facilitated carrier diffusion type ii

Answer 6

Glut-1- glucose diffusion
1. glut-1 faces the outside with its binding site
2. glucose binds to glut-1 from outside
3. a conformational change occur (close one hole- open the other), transporting glucose to the interior
4. then, glucose is released

Question 7

what is active transport? and the types of active transport?

Answer 7

Using energy to transport molecules AGAINST an electrochemical gradient
1. active transport protein carriers
2. endocytosis (phagocytosis) & pinocyotsis

Question 8

What is cotransport? and what are the two types of cotransport?

Answer 8

*can be passive/ active depending on the molecules & pumps
involves the obligatory coupled transport of 2 different solutes with the help of a carrier protein

symport: both solutes move in the same direction
antiport: solutes in opposite directions

Question 9

Na+/ Glucose symporter

Answer 9

PASSIVE + symport
initial state: pump is open to outside
1. a sodium ion is bound

2. glucose is then bind to the pump due to Na+ stimulation->causing a conformational change

3.pump is open to inside

4. Na+ is released inside (but is continuously forced outside by Na/K pump
5. Loss of Na+ causes glucose to release to inside
6. release of glucose stimulates return to initial state

Question 10

Sodium/potassium pump

Answer 10

an example of active transport antiporter (ACTIVE + antiporter)
3 Na+ out/ 2 K+ in

initial state: pump open to inside
1. 3 Na+ are taken from inside

2. ATP phosphorylates alpha subunits (atp-> adp+pi)
3. A conformational change expels 3Na+ to outside

-pump open to outside, ready to start second half of cycle

4. 2 K+ accepted from outside
5. Dephosphorylation triggers another conformational change
6. 2 K+ expelled to insides-> pukp return to initial state

Question 11

How do direct & indirect active transport work

Answer 11

direct: active transport of protons from inside (low) to out (high) with ATP (ADP+Pi)

indirect: transport of solute molecules from outside (low) to outside (high)

Question 12

endocytosis

Answer 12

food/water

*receptor-mediated: bind to proteins on the surface to bring inside

Question 13

pinocytosis

Answer 13

water

Question 14

phagocytosis

Answer 14

immune sys.
-phagocytes (macrophages)