Week 5- transport across membranes- Drewes

Question 1

GLUT 1

GLUT 4

Answer 1

1- RBC

4- fat, muscle (including heart) and insulin sensitive

Question 2

Na+/K+ pump

Answer 2

requires energy to transport 3 sodiums out of cell and 2 potassium into cell

Question 3

Na+/glucose symporter

Answer 3

uses the energy of Na+ moving down its [ ] gradient to power glucose moving up its concentration gradient

Question 4

how is ATP directly involved in the Na+/K+ shuttle

Answer 4

Na+ attaches to transporter ⇒ ATP P’s the transporter ⇒ conformational change allows Na+ to be moved to outside of the cell ⇒ 2 K+ go into the P’d transporter ⇒ the P is removed and a conformational change allows 2 K+ to come into the cell

Question 5

Distinguish the unique features of the sodium-potassium ATPase.

Answer 5

• use energy to pump 3 Na+ out and 2 K+ in (pumped against gradient)
  
  • this establishes the electrochemical gradient and resting membrane potential

-ATP is directly involved

Question 6

Compare passive diffusion and facilitated diffusion.

Answer 6

• passive diffusion
• can freely move through the membrane
• doesn’t require ATP
• if you increase the [ ] you will increase the velocity (not saturable)
• facilitated diffusion
• doesn’t require ATP
• if you increase the [ ] you don’t always increase the velocity (at some point you will reach a max velocity- when all the proteins are full) (saturable)
• examples: pores, gated channels, carrier proteins

Question 7

Calculate the free energy change associated with transport

Answer 7

-ΔG= movement down a [ ] gradient
\+ΔG= movement against a [ ] gradient

Question 8

drug that inhibit Na+ K+ channel

Answer 8

digotoxin

Question 9

Compare primary versus secondary active transport.

Answer 9

• Primary → directly hydrolyzes ATP

- Secondary → uses the energy of another molecule to move against concentration gradient

Question 10

Describe the mechanism of ionophores.

Answer 10

2 proteins that come together in the membrane to form a pore for ions to transport through. This is typically used in drugs as an antibacterial or antiviral.

Question 11

Describe ligand-activated ion channels

Answer 11

Ligand-activated ion channel has a binding site for ligand (drug or other substrate), and when the ligand binds to the receptor, the channel opens and allows for flow of ions

Question 12

Distinguish the differences between channels and pumps.

Answer 12

Channels → specific for 1 molecule, can be open or closed, molecules move down concentration gradient
Pumps → specific for molecules, use energy to power, molecules move against their concentration gradient

Question 13

normal function of CFTR

Answer 13

allow Cl- transport across the cell membrane AND to regulate transport of other ions via interactions with their transport proteins

Question 14

diagnosis for cystic fibrosis

Answer 14

skin will be salty

Question 15

Postulate the mechanism for opening voltage-sensitive channels.

Answer 15

Leak channels can cause change in voltage of membrane potential, which can trigger voltage sensitive channels to open

Question 16

Describe why ion channels are considered allosteric proteins

Answer 16

When an ion binds to the channel, it can cause a conformational change that allows the channel to open.

Question 17

Suggest how channels can be selective

Answer 17

Depending on the charge of amino acids that line the channel, you can get selectivity via interactions between ion and the amino acids

Question 18

Compare in molecular terms a Na+, K+, and Ca2+ channel

Answer 18

Na+ and Ca++: very similar- 4 repeats of a 6 transmembrane domain; voltage gated
-K+: one 6 transmembrane seq.; ethyl groups cause plugging of the channel

Question 19

cystic fibrosis

Answer 19

cystic fibrosis: mutation in the CFTR gene (loss of a phenylalanine at F508)

• this mutation causes defect in Cl- channels: doesn’t allow Cl- to be reabsorbed so it all goes to the surface (why ppl will taste salty that have this)
• have this problem in the lungs as well: Cl- wont allow mucus to clear properly ⇒ becomes a breeding ground for bacteria ⇒ people with this die of bacterial infections