Lecture 8- Biological Membranes

Question 1

What is normal plasma osmolality range?

Answer 1

280- 310 mOsm or mmol/Kg water

Osmolality already takes into account that it is in 1 kg of water

Question 2

What can diffuse through the capillary wall but not the cell membrane?

Answer 2

Sodium and potassium

Question 3

Membrane permeability ranking?

Answer 3

Hydrophobic molecules eg O2 and CO2

Small uncharged polar- H2O

Large uncharged polar- glucose

Ion and charged polar molecules- RNA and DNA ATP, proteins and Sodium, potassium, chloride, calcium etc

Question 4

What is Flux?

Answer 4

A measurement of how fast a solute will move across a membrane.

Rate of diffusion of uncharged solute will be directly proportional to rate of change of concentration with distance in direction of flow

No gradient= equilibrium= no net flux

Question 5

What factors affect diffusion?

Answer 5

Directly proportional to surface area of barrier and inversely proportional to thickness of barrier

Question 6

What is facilitated diffusion?

Answer 6

When no energy it’s required but movement occurs through a protein channel

Question 7

How are large molecules moved across membranes?

Answer 7

Through exocytosis, pinocytosis and endocytosis. These processes require energy and some are receptor mediated

Question 8

What is an osmole?

Answer 8

Measure of solutions ability to create osmotic pressure and thus effect movement of water.

1 mole glucose= 1 osmolar solution in 1kg water

1 mole CaCl2= 3 osmolar solution in one kg water

Question 9

How can you estimate serum osmolality in clinical practice?

Answer 9

Double serum sodium

Question 10

What are aquaporins?

Answer 10

Channels in membranes that allow facilitated diffusion of water. They are not ion channels. Have positively charged amino acids in centre of channel to prevent hydrogen ions from passing through