Lecture 4: Membrane Dynamics and Membrane transport

Question 1

Phospholipids can easily move —- within the same leaflet

Answer 1

laterally

Question 2

Phospholipid “flip-flopping” to the other leaflet is — (—–)

Answer 2

• restricted
• (transverse diffusion)

Question 3

Why is it thermodynamically unfavourable for phospholipids to flipflop to the other leaflet

Answer 3

Polar hydrophillic head has to pass to the non-polar region

Question 4

Passive transport (2)

Answer 4

• Does not require energy input from the cell
• Occurs by diffusion (Movement from a region of high concentration to low concentration)

Question 5

Active transport (2)

Answer 5

• Does require energy input (ATP)
• Can move substances against a concentration gradient

Question 6

Diffusion

Answer 6

The spontaneous process in which a substance moves from an area of higher concentration to one of lower concentration, eventually reaching the same concentration in all areas (equilibrium)

Question 7

Concentration gradient

Answer 7

The difference in the concentration of a substance between two areas

Question 8

Simple diffusion through the lipid bilayer. what can penetrate the bilayer? + ex (2)

Answer 8

• Small inorganic solutes, solutes with high lipid solubility
• O2, CO2, H2O

Question 9

Simple diffusion through the lipid bilayer. what cannot penetrate the bilayer? + ex (2)

Answer 9

• Ions and polar organic solutes (sugar and amino acids)
• Anything too large

Question 10

Osmosis:

Answer 10

Water moves through a membrane from a region of lower solute concentration to a region of higher solute concentration

Question 11

Hypertonic solution

Water movements?

Answer 11

Higher solute concentration outside of the cell

H2O leaves the cell

Question 12

Hypotonic

Water movements?

Answer 12

Lower solute concetration outside of the cell

Water goes in cell

Question 13

Isotonic solution

Answer 13

Equal solute concentration

Question 14

Aquaporin

Answer 14

• Channel proteins that faciliate the transport of water
• Allows cells to be more permeable to water than is possible by diffusion through the bilayer

Question 15

Ion channels (3)

Answer 15

• A transmembrane structure permeable to a specific ion or ions
• Most are highly selectibe
• Most ion channels are gated: change conformation to be open or closed

Question 16

Voltage-gated

Answer 16

Open/close depends on the differene in ionic charge on either side of membrane

Question 17

Ligand-gated +ex (3)

Answer 17

• Open/closed depends on the binding of a specific molecule (a ligand)
• The ligand is usually not the solute that is passing through the channel
• Eg: Neurotransmitter (acetylcholine) is a ligand that binds to ion channels

Question 18

Volatge

Answer 18

difference in charge between two compartments

Question 19

Mechano-gated

Answer 19

• Open and closed depends on mechanical forces
• Ex: Stretching, channels involved in hearing, sound waves etc