002 Processes at Membranes

Question 1

What 4 factors affect membrane permeability of a substance?

Answer 1

Lipid solubility of diffusing substance
Size and shape of diffusing surface
Temperature
Membrane thickness

Question 2

What 2 types of protein can carry out facilitated diffusion?

Answer 2

Carrier proteins and Ion channels, both selective (even stereoselective) for the transported molecule.

Question 3

What are the two main driving forces?

Answer 3

Chemical driving force created by ion concentration difference. Electrical force caused by excess charge on one side. These two form the electrochemical equilibrium.

Question 4

What are the 3 main types of carrier proteins?

Answer 4

Uniporters, Antiporters, Symporters

Question 5

What are uniporters?

Answer 5

Carrier proteins that only transport one molecule

Question 6

What problem does sodium cause for potassium channels? How is this solved?

Answer 6

Na+ is a smaller ion with the same charge as K+. To prevent flow of Na+ in K+ ion channels, carbynol only binds to K+ as Na+ is too small. Na+ also requires more energy to be pulled.

Question 7

Explain how the Na+/K+ pump works.

Answer 7

This undergoes primary active transport by using direct use of ATP. Binding of Na+ to the pump stimulates phosphorylates ATP, causing protein to change shape. Shape expels Na+ to the outside and extracellular K+ binds, which triggers the release of phosphate group. This restores the original conformation of the pump protein. K+ is released and Na+ sites are ready to bind again.

Question 8

Explain the importance of the Na/glucose transporter.

Answer 8

Na gradient is used as energy to pump glucose against its concentration gradient. This protein also allows sodium to be transported out of the lumen of the gut.

Question 9

What is the normal resting potential for a body cell?

Answer 9

-40 and -90mV (-75mV) occuring near a membrane

Question 10

Outline the difference between ionotropic and metabotropic receptors.

Answer 10

Ionotropic receptors are ligand gated ion channels that open when an agonist binds to extracelular aspect of the protein.
Metabotropic receptors are coupled to intracellualr signalling. When agonist binds, it activates enzymes whos catalytic site faces the cytosol e.g. insulin and beta receptors like G-protein.

Question 11

What is the main function of the Na+/K+ pump?

Answer 11

This is a primary active transport that creates a gradient to power secondary active transport (Na+/glucose symporter)

Question 12

Where are the CFTR binding sites found on?

Answer 12

Intracellular ligand gated ion channels

Question 13

Give an example of an uniporter and where they are found

Answer 13

GLUT 1, GLUT4 ligand bind glucose flips transporters to release glucose on other side in muscles.

Question 14

Give an example of a symporter and where they are found

Answer 14

Na+ is used as an energy to pump glucose against the concentration gradient allowing glucose to be transported out of the lumen.

Question 15

Give an example of an antiporter and where they are found

Answer 15

Band 3 protein transporting HCO3-/Cl-. This protein binds to spectrin, instigating electroneutral transfer of CO2 and HCO3 found in RBC.

Question 16

In a Na+/K+ pump, for how many Na+ ions are moved out for K+ moved in?

Answer 16

3 Na+ ions moved out for every 2 K+ ions pumped in

Question 17

How many cycles per second do the Na+/K+ channel go through per second?

Answer 17

100 cycles per second

Question 18

What is ouabain?

Answer 18

Na/K+ pump blocker

Question 19

How does the Na+/glucose symporter work?

Answer 19

The gradient generated by the primary Na+/K+ pump creates a gradient that powers the inward flux of glucose against its gradient. 2 Na+ ions are used for one glucose in the gut where there is low concentrations in the gut lumen compared to enterocyte. The Na+ movement into the enterocyte drives glucose by passive movement.