Week 5- transport across membranes- Drewes Flashcards
GLUT 1
GLUT 4
1- RBC
4- fat, muscle (including heart) and insulin sensitive
Na+/K+ pump
requires energy to transport 3 sodiums out of cell and 2 potassium into cell
Na+/glucose symporter
uses the energy of Na+ moving down its [ ] gradient to power glucose moving up its concentration gradient
how is ATP directly involved in the Na+/K+ shuttle
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
Distinguish the unique features of the sodium-potassium ATPase.
- 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
Compare passive diffusion and facilitated diffusion.
- 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
Calculate the free energy change associated with transport
-ΔG= movement down a [ ] gradient \+ΔG= movement against a [ ] gradient
drug that inhibit Na+ K+ channel
digotoxin
Compare primary versus secondary active transport.
- Primary → directly hydrolyzes ATP
- Secondary → uses the energy of another molecule to move against concentration gradient
Describe the mechanism of ionophores.
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.
Describe ligand-activated ion channels
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
Distinguish the differences between channels and pumps.
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
normal function of CFTR
allow Cl- transport across the cell membrane AND to regulate transport of other ions via interactions with their transport proteins
diagnosis for cystic fibrosis
skin will be salty
Postulate the mechanism for opening voltage-sensitive channels.
Leak channels can cause change in voltage of membrane potential, which can trigger voltage sensitive channels to open
Describe why ion channels are considered allosteric proteins
When an ion binds to the channel, it can cause a conformational change that allows the channel to open.
Suggest how channels can be selective
Depending on the charge of amino acids that line the channel, you can get selectivity via interactions between ion and the amino acids
Compare in molecular terms a Na+, K+, and Ca2+ channel
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
cystic fibrosis
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
