Session 2 - Transporters, Ion Channels And Pores

Question 1

Define a semi permeable membrane

Answer 1

A layer through which only allowed substances can pass

Question 2

What types of molecules can permeate a lipid bilayer?

Answer 2

Hydrophobic molecules: O2, CO2, N2, Benzene

Small uncharged poplar molecules: H2O, Urea, Glycerol

Question 3

How do proteins contribute to membrane permeabililty?

Answer 3

Proteins increase the the permeability of the membrane to allow specific large and polar molecules through. They also allow for controlled permeability. I.e the permeability can be regulated

Question 4

What factors determine whether something needs to be passively or actively transported?

Answer 4

This is dependant on the concentration ratio and the membrane potential (the electrochemical gradient)

Question 5

How is energy supplied for active transport?

Answer 5

Via ATP. This can be direct or indirect. Indirect is where ATP is use to create a concentration gradient; which is then used in co-transport to carry another molecule against its concentration gradient.

Question 6

Who does water permeate across a lipid bilayer?

Answer 6

Water is a small and uncharged (but slightly polar) molecule so it is able to pass through the membrane. It moves via osmosis (diffusion of water) driven by the osmotic gradient of solutes

Question 7

Which direction do most free ions move if they were able to move to their equilibrium? And what exceptions are there?

Answer 7

Most ions move into the cell (Na+, Ca2+, Cl-) but K+ moves out of the cell it has a higher concentration in the cell compared to out of the cell

Question 8

What are the Intracellular and interstitial free on concentrations of cells?

Answer 8

Interstitial/ Intracellular

Na+ = 145mM>12mM
K+ = 4.5mM<140mM
Cl- = 123mM > 4mM
Ca2+ = 1.5mM > 10^-7M

Question 9

What terms are used to describe the differences in concentrations of solutions?

Answer 9

Isotonic - same solute
Hypotonic - less solute
Hypertonic - more solute

Question 10

Define osmole, osmolality and osmotic pressure

Answer 10

Osmole = measure of a solutes ability to create an osmotic pressure and thus affect the movement of water. 1 mole of non-ionisable substance = 1 osmole. I.E. 1 mole of CaCl2 = 3 osmolar solution in 1L solution of water

Osmolality = the osmolar concentration of a solution when expressed in osmoles per kilogram

Osmotic pressure - the pressure required to stop the flow of water

Question 11

What membrane protein facilitates water diffusion?

Answer 11

Aquaporins