3.1 Transporters (ATP-driven Pumps)

Question 1

F-type ATPase

Answer 1

catalyze uphill passage (intermembrane space to cytosol) of proteins with ATP hydrolysis (makes ATP)

Question 2

structural subunits of F-type ATPase

Answer 2

Fo - provides transmembrane pathway
- subunit a (proton half-channels)
- subunit b (arm)
F1 - uses energy of ATP to drive protons uphill 
- subunit c (proton binding site)

Question 3

steps of proton translocation (5 steps)

Answer 3

1) proton from periplasmic space move towards half-channel with - Asp
2) proton fills empty proton-binding site and displaces Arg side chain, swings over to filled proton-binding site on subunit c. Proton at next site is displaced
3) displaced proton moves through half-channel II,and exits into matrix
4) counterclockwise rotation of entire c ring moves empty c subunit over half-channel I
5) process repeated

Question 4

does F-type ATPase do uphill or downhill transport

Answer 4

uphill transport of protons

Question 5

F-class proton pumps found in (3)

Answer 5

1) bacterial PM
2) inner mitochondrial membrane
3) thylakoid membrane of chloroplast

Question 6

V-class proton pumps found in (3)

Answer 6

1) vacuolar membranes in plants/yeast/fungi
2) endosomal/lysosomal membranes in animal cells
3) PM of osteoclasts+kidney tubule cells

Question 7

V-class ATPase function

Answer 7

acidifying intracellular components (lysosome, endosomes, Golgi, secretory vesicles)
- uses ATP to pump H+

Question 8

P-type ATPase function

Answer 8

maintain ionic differences

• phosphorylated by ATP
• includes: (Na/K antiporter, H/K antiporter, Ca2+)

Question 9

concentration gradient of K+ across cell

Answer 9

10-30 times higher inside cell than outside

Question 10

concentration gradient of Na+ across cell

Answer 10

10-30 times higher outside cell than inside

Question 11

where is the NaK pump found

Answer 11

PM of all animal cells

Question 12

Na+/K+ pump

Answer 12

ATP-driven antiporter: pumps Na+ out and K+in

Question 13

SERCA

Answer 13

Ca2+ ATPase for muscle contraction

Question 14

how does SERCA work

Answer 14

1) rapid influx of Ca2+ triggers opening of Ca2+ channels on PM
2) Ca2+ ATPase on SR (ER of muscle cells) pumps Ca2+ into SR and muscles can contract

Question 15

SERCA structure

Answer 15

single polypeptide, 10 TMS

• N domain binds ATP and Mg2+
• P domain contains Asp characteristics of P-type ATPases
• A domain communicates movements between N and P domains

Question 16

ABC Transporters structure

Answer 16

• 2 nucleotide binding sites in cytosol (homodimer or heterodimer)
• 2 transmembrane domain (can vary in length)
• binding site for 2 ATP

Question 17

ABC Transporter function

Answer 17

transport of sugars, vitamins, amino acids, etc from cytosol to extracellular space (in humans)

Question 18

ABC Transporter mechanism steps (3)

Answer 18

1) substrate from cytosol binds to inward-facing site between TMS
2) 2 ATPs bind to ATP binding sites of the 2 nucleotide binding domains
3) ATP stabilizes dimerization of NBD
4) 90 degree rotation of ABC and the substrate released in the extracellular space
5) ATP hydrolysis
6) Pi and ADP released

Question 19

MalE

Answer 19

Maltose binding protein in gram negative bacteria: captures maltose in periplasm and brings to ABC transporter on IM

Question 20

Maltose transporter

Answer 20

ABC transporter in gram negative bacteria

- transports maltose from periplasm space to cytosol with use of 2 ATP

Question 21

for ABC transporters, how are more hydrophobic substrates handled?

Answer 21

more hydrophobic substrates are more embedded into the lipid bilayer

Question 22

MsbA

Answer 22

(lipid flippase) - ABC transporter that exports a lipid from inner leaflet to outer leaflet

Question 23

how was the activity of MsbA investigated with ATP

Answer 23

1) fluorescent phospholipids were added to membrane
2) some cells given ATP, some not
3) adding non-membrane-permeating quenching compound
4) the ones given ATP showed greater fluorescence because the flippase MsbA flipped some of the fluorescent phospholipids inside

Question 24

TAP transporter

Answer 24

1) foreign proteins are degraded
2) recognized by TAP1 and TAP2
3) peptides translocated to ER lumen and loaded onto MHC1
4) MHC1 displayed on PM for macrophages to kill the cell

Question 25

CFTR

Answer 25

“Cystic fibrosis transmembrane conductance regulator”. ABC transporter. But functions as Cl- channel in PM of epithelial cells. Cl- from cytosol to outside
- maintains normal salt concentrations of the mucous layer of the airway for proper hydration so cilia can remove bacteria from air we breathe

Question 26

what does the R-domain the CFTR do?

Answer 26

regulatory region that controls channel activity of the transporter by blocking the entry door of the channel (Cystic fibrosis transmembrane conductance regulator). Always found in cystic fibrosis

Question 27

cystic fibrosis

Answer 27

common hereditary disease where the normally thin layer of mucus that coats the internal surface of the lungs is unusually thick and sticky due to accumulation of bacterial infections because the cilia can’t remove the bacteria from the mucous layer