Minimals: membrane transport

Question 0

What does it mean that lipids are amphipathic?

Answer 0

They consist of hydrophobic and hydrophilic parts

Question 1

What is the permeability constant?

Answer 1

The permeability constant is the amount of material transported through the membrane per unit surface in unit time due to unit concentration

Question 2

What are the possible forms of motion of a lipid molecule in a membrane?

Answer 2

Lateral diffusion
Rotational diffusion
Transmembrane flip-flop
Flexible motion of fatty acid side chains

Question 3

What are the possible phase states of biological membrane?

Answer 3

Gel phase

Liquid crystal/fluid phase

Question 4

What changes in the properties of the fatty acid side chains increase the transition temperature of a membrane?

Answer 4

Increase in the saturation of fatty acid carbon-carbon bonds
Increase in the length of the fatty acid side chains

Question 5

How does cholesterol change the fluidity of lipid membrane?

Answer 5

Below the phase transition temperature it usually increase, above the phase transition temperature it decreases

Question 6

What is the magnitude of the lateral diffusion constant of lipids and proteins in biological membranes?

Answer 6

Lipids 10^-8 ~ 10^-9 cm^2/s

Proteins 10^-9 ~ 10^-12 cm^2/s

Question 7

Which methods can be used to measure the lateral diffusion of proteins in biological membranes

Answer 7

Fluorescence recovery after photobleaching (FRAP)

Single particle tracing (SPT)

Fluorescence correlation spectroscopy (FCS)

Question 8

For what kind of molecules is the permeability of biological membranes the highest?

Answer 8

For small, uncharged, apolar molecules.

Eg. O2 N2

Question 9

How can membrane proteins be classified based in their function

Answer 9

Transport and channel protein
Receptor and signal transducing protein
Enzymes
Structural membrane proteins

Question 10

What is passive transport

Answer 10

Transport processes driven by the electrochemical potential gradient which do not need active metabolism

Question 11

What is active transport

Answer 11

Transport processes that results in material flow against their electrochemical potential gradient at the expense of energy utilization.

Question 12

What is primary active transport

Answer 12

The transporter pumps ions/molecules across the membrane against their electrochemical gradient using energy from ATP hydrolysis o

Question 13

What is secondary active transport

Answer 13

Secondary active transport moved ions/molecules across the membrane against their gradient using energy stored in the gradient of another ion created by primary active transport mechanism

Question 14

What is simple diffusion across biological membrane

Answer 14

The passive transport of small and lipid-soluble molecules across the membrane

Question 15

What is facilitated diffusion

Answer 15

The passive transport of meme brand impermeant ions/molecules across the membrane aided by transport proteins(ion channels or carriers) molecules

Question 16

What are the properties of facilitated or carrier mediated diffusion?

Answer 16

Transporter proteins specifically bind the transporter molecules

The transport can be selectively inhibited

The flux of transport can be saturated over a given concentration of the transported material

Question 17

What kind of ion channels do you know based in their mode of activation

Answer 17

Ligand gated ion channels 
Voltage gated ion channels 
Second messenger gated ion channels 
Mechanical deformation (stretch) activated ion channels

Question 18

What is the function of ionophores

Answer 18

They promote the selective transport of ions through lipid membrane

Question 19

How can ionophores be grouped according to the mechanism of ion transport

Answer 19

Carrier ionophores

Channel forming ionophores

Question 20

List the factors contributing to the maintenance of quiescent membrane Potential

Answer 20

Diffusion potential
Donnan potential
Active transport by ion pumps

Question 21

What is the equilibrium potential of an ion?

Answer 21

The membrane potential where the net flux of the given ion is zero.
The system is in thermodynamic equilibrium for the given ion.

Question 22

Are the ions on the two sides of the membrane of a living cell in thermodynamic equilibrium? Why?

Answer 22

No. There is no thermodynamic equilibrium because the net passive flux of a given ion is not zero at the resting membrane potential.

Question 23

Give the definition and the unit of flux

Answer 23

Flux (J) is the amount of transported items across unit cross section area per unit time. Unit: mol/(m^2s)

Question 24

Give the definition and unit of conductivity

Answer 24

G(conductivity)=1/R
R is resistance
Unit: 1/omega=Siemens(S)

Question 25

Define the action potential and interpret the ionic basis of its generation.

Answer 25

The action potential is a characteristic, time-dependent change in the membrane potential as a result of time and membrane potential dependent changes in the ion permeability so of the membrane. In the depolarization phase the Na+ permeability is dominant, the subsequent depolarization is the result of concurrent decrease in Na+ permeability and an increase in Ka+ permeability.