membrane transport

Question 1

What are intrinsic membrane proteins ?

Answer 1

transport
channels
carriers
pumps

Question 2

Define channel ?

Answer 2

mediate passive transport
-transient binding
-opens all the time

Question 3

Define carriers ?

Answer 3

carry out either passive or secondary active transport
binds transported species for longer
not open all the time

Question 4

Define pumps ?

Answer 4

use molecular energy source to move species across menranes
ie:primary active transport

Question 5

What is the energy of concentration gradients ?

Answer 5

For an uncharged solute
ΔG =RTln(c2/c1)
if c1>c2 than ΔG<0
downhill transport

Question 6

How does the energy of a charged concentration gradient ?

Answer 6

cations experience downhill driving force towards side of lower concentration and or lower potential

Question 7

What is the potassium channel ?

Answer 7

[K+] is held high inside cells
The K+ channel allows K+ ions to flow out of a neuron
-passive transport down conc gradient
happens during repolarisation of action potential

Question 8

What is the potassium selectivity filter ?

Answer 8

responsible for selective and rapid conduction of K+
k+ ions lose bound water in the selectivity filter

Question 9

What are the energetics of K+/Na+ selectivity ?

Answer 9

Peptide carbonyls bind more strongly than water to K+ Smaller Na+ binds more weakly to filter sites so Na+ remians solvated –cant enter the selectivity filter

Question 10

What is E.coli lactose permease and how it works ?

Answer 10

lactose permease is a carrier which mediates secondary active transport -secondary transporter
uses thermodynamically downhill flow of protons to drive the uphill flow of lactose
both species move into cell so LP -symprter
protons drive lactose import through a cycle of binding and unbinding events

Question 11

How E.coli lactose permease works?

Answer 11

1. Proton binds to outer face of proteins
2. Protonated outer face binds lactose
3. Lactose binding drives eversion
4. Lactose lost to cyptoplasm
5. Proton lost to cyptoplasm
6. proton lost drives eversion

Question 12

What is SERCA :a P type ATPase ?

Answer 12

sarcoplasmic reticulam Ca2+ATPase
hydrolyses ATP to transport Ca2+ from cyptoplasm back into sarcoplasmic reticulam (SR) of muscle cells
Critical in terminating muscle contraction
SERCA inhibitors are highly toxic
Atp hydrolysis drives structural change in SERCA through a cycle of binding events

Question 13

Structure of SERCA ?

Answer 13

1 polypetide chain ,4 domains

Question 14

How SSERCA works ?

Answer 14

1. Calcium bind to transmemebrane domain from cyptoplasm
2. ATP binds at N domain
3. ATP hydrolysis
4. ADP ,Ca2+ loss into SR -E1–>E2 eversion
5. Phophate loss
6. E2–>E1 “eversion”

Question 15

Are other P-type ATPases similar ?

Answer 15

Yes they work in a similar way
sodium-potassium pump
ATP-hydrolysis druves eversion-protein opens on 1 side closes on the other
1 Mole of ATP hydrolysis can pump 3 mol Na+ out of cell &2 mol K+ into cell