FORM & FUNCTION (Membrane Permeability)

Question 1

effective olsmolarity

Answer 1

-depends on impermeable solutes only

Question 2

relative effective osmolarity

Answer 2

-between two compartments determines whether water movement will be initiated

Question 3

permeability of lipid bilayer depends on

Answer 3

1. Size and polarity effects diffusion rate
2. Impermeable to charged ions unlesss they’re membrane transporters
3. pH can affect the permeability of weak acids and bases
   *most molecules important for cell function are polar and large, they require membrane transporters to get into cells at a reasonable rate

Question 4

size and polarity

Answer 4

-smaller and more hydrophobic =diffuse faster
-gases diffuse across membrane rapidly

Question 5

types of membrane transport proteins

Answer 5

1. Channels
2. Passive transporters
3. Active pumps

Question 6

channels basic

Answer 6

-discriminate mainly based on size and charge
-move solute down it’s electrochemical gradient

Question 7

passive transporters basic

Answer 7

-more selective based on how well a molecule fits to the binding site (similar to enzymes)

Question 8

acitve pumps basic

Answer 8

-requires energy (ATP) to pump molecules AGAINST it’s electrochemical gradient

Question 9

features of ion channels

Answer 9

-specific type of passive transporter
-selective by size and charge
-mediate passive flux of ions across membrane
-high permeation rate when open
-some channels are gated

Question 10

leaky channels

Answer 10

-always open
-no gating mechanism
-all cells contain them

Question 11

4 major gating signals

Answer 11

1. ligand (Ach)
2. 2nd messenger (Ca2+)
3. Mechanosensitive (stereocilia in hair cells)
4. Voltage (Na+, K+, Ca2+)

Question 12

active transport

Answer 12

-moves molecules against concentration and electrical gradients
-energy required
-Na+/K+ ATPase is the most important type (*accounts for 30% or more of the total ATP consumption of animals

Question 13

Na/K ATPase

Answer 13

1. Transporter binds 3Na+ from cytosol
2. phosphorylation of ATP causes a conformational change
3. Na+ is released and 2 K+ bind
4. deposphorylation favours original conformation
5. K+ released to cytosol
   *electrogenic activity: produces negative charge inside cell relative to outside

Question 14

active ion transport prevents osmotic diaster in cells

Answer 14

1. Anionic sites on impermeable intracellular macromolecules must be balanced by intracellular cations (Na+, K+, Mg2+, Ca2+)
2. Osmotic pressures inside the cell is higher than extracellular component
3. Avoid osmotic diaster because Na+ and Ca2+ continuously pumped out of the cell

Question 15

higher osmotic pressure inside the cell

Answer 15

=osmotic movement of water (lysis)

Question 16

Na+ and Ca2+ continuously pumped out of the cell

Answer 16

-gives same effect as Na+ and Ca2+ impermeability
*steady state: true osmotic equilibrium is NEVER reached
*requires energy to regulate the volume

Question 17

secondary active transport

Answer 17

-electrochemical Na+ gradient generated by Na+ pump can drive the active transport of a second solute
1. Antiport
2. Symport

Question 18

number of transporters

Answer 18

-determines permeability of solute
-more transporters=more permeable a solute will be

Question 19

paracellular transport

Answer 19

-movement between cells
-passive
-driven by gradients
-regulated by later junctions between endothelial cells

Question 20

variable permeability

Answer 20

-multicellular membrane can have various permeability points
-junctions can change between diseases
*changes in response to physiological changes (DYNAMIC)

Question 21

multicellular membrane permeability

Answer 21

1. In some structures regulating passage is complex (blood vessels, GI tract, respiratory tract, kidneys, blood-brian barrier)
2. Number of junctions on lateral surface of epithelial cells is one of many mechanisms influencing this regulation