Active transport

Question 1

What is the banana rocking mechanism?

Answer 1

Binds 3 Na at inner face of membrane
+ve charges causes change in conformation so Na sealed into pocket
ATP binds which brings negative P
Negative charge causes conformation change - bananas rock and Na face outside of cell
Na unbinds
Act of Na unbinding induced conformation change so K is preferentially bound
2 K+ bind
+ve charge in protein causes conformation charge so 2K sealed in pocket, and released to inner face of cell
Rotates this carrier cycle driven by energy from ATP phosphorylation (on aspartate)
K allows dephosphorylation to occur (Na allows phosphorylation)

Question 2

What is a Na/K inhibitor?

Answer 2

ouabain

Question 3

What are the 2 forms of Ca-atpase?

Answer 3

SERCA - sarco/endoplasmic reticulum membrane
PMCA - plasma membrane
act to lower ca in cytoplasm

Question 4

What are the properties of the ca-atpase?

Answer 4

1 ATP extrudes 1 Ca from cytoplasm to outside cell or inside sarcoplasm in return for 2 H+
has high affinity (Km 150 nM for Ca) but slow

Question 5

How much energy is obtained from ATP?

Answer 5

50 kJ /mole

Question 6

What is the net transfer of charge with Ca-atpase movement?

Answer 6

none

Question 7

What is normal extracellular pH?

Answer 7

7.4

Question 8

What is the average intracellular pH?

Answer 8

7.1

Question 9

How frequently is the Ca-atpase cycle carried out?

Answer 9

~20 ms

Question 10

What is the mechanism of Ca movement in Ca-atpase?

Answer 10

Ca binds protein in cytoplasm
Induces conformational change allowing ATP to bind
ATP brings negative P close to cytoplasmic part of protein
Ca “spat out” other side of membrane

Question 11

Which atpase usually runs backwards?

Answer 11

mitochondrial H+ ATPase

at expense of H gradient - generating by proton pumping fuelled by metabolism

Question 12

What is the potential inside mitochondrion?

Answer 12

-200 mV (H+ high outside, low inside so big proton gradient pulling H+ inside)

Question 13

How does the Na-Ca exchanger work?

Answer 13

uses power from 3 Na moving into cell to extrude 1 Ca

fast / low affinity

Question 14

Is calcium higher or lower in rods and cones?

Answer 14

Ca needs to be lower

therefore Na/Ca transports 4 Na for every Ca leaving cell

Question 15

What drives GABA uptake?

Answer 15

Na and Cl- cotransport (2Na, 1Cl)

no enzyme

Question 16

Why must GABA be kept low?

Answer 16

it needs to be lowered below the affinity of GABA receptors so there is not constant inhibition except in specific areas where GABA channels are always opened: parts of cerebellum, hippocampus

Question 17

What is the energy needed to move GABA?

Answer 17

2 Na down conc gradient 11.8 kJ
1 Cl down conc gradient 5.9 kJ
1 +ve charge entering cell 5.8 kJ/mole
RT.ln[i]/[o] = 5.9 kJ/10 fold gradient