1-Membrane Transport

Question 1

membrane

function

Answer 1

1. create chemical compartments by acting as barrier
   -uneven distribution of molecules across membrane
2. conduit for molecules

Question 2

non-vesicular transmembrane transport

Answer 2

1. passive: no energy
   -diffusion thru lipid bilayer, channels, or facilitated (carriers)
2. active: energy required
   -primary (ATPase), secondary (sym/antiporters)

Question 3

vesicular transmembrane transport

Answer 3

aka endo/exocytosis forr bulk transport

mediated by lipid vesicles, energy required

Question 4

simple diffusion

Answer 4

-straight thru bilayer
-only gases + small uncharged

Question 5

simple diffusion factors

Answer 5

1. lipid solubility
2. molecular size
3. cell membrane thickness
4. concentration gradient
5. membrane surface area
6. composition of lipid bilayer

O2/CO2 inverse proportion to thickness and size, rest are direct

Question 6

diffusion thru channels
types of molecules

Answer 6

1. small, uncharged molecules
   -affected by # of water channels, water selectivity, water down concentration gradient
2. ions
   -affected by # of ion channels, ion selectivity, moves down electrochemical gradient

Question 7

aquaporin

Answer 7

channel specific to water

mediates water permeability of cell membrane, regulate by insert or remove channel

4 subunites = functional channel = fast transport rate

Question 8

osmosis

Answer 8

movement of water across water permeable membrane

water follows osmotic pressure (high > low)

Question 9

nephrogenic diabetes insipidus

NDI

Answer 9

mutation in aquaporin-2 gene so reabsorption of water in kidney compromised
-normally vasopressin or ADH signals aquaporins to move to apical surface to absorp water

-excrete large amounts diluted urine + xs thirst

Question 10

gating mechanisms

ion channels

Answer 10

1. no gate
2. voltage gating
3. ligand gating (extra/intracellular)
4. mechanically gated

Question 11

uniporters

facilitated diffusion

Answer 11

-transport is substrate specific
-changes affinity for subtrate based on configuration
-higher rate than simple diffusion
-has maximum transport rate (Vmax)
-reversible

Question 12

transport rate factors

Answer 12

1. concentration gradient (equil @ Vmax)
2. # transporters (direct prop to Vmax)
3. binding affinity (inverse to Km)

small Km = high affinity = fast transport

Question 13

diabetes mellitus type I

glucose transporters

Answer 13

insulin deficiency > inadequate transporters on cell membrane = hyperglycemia in blood/urine

normal: insulin inc glucose transporters on cell membrane for uptake from bloodstream

Question 14

primary active transport

Answer 14

via carrier proteins and energy
-uncharged moles vs concentration gradient
-ions vs electrochemical gradient

carrier proteins are similar to diffusion ones

Question 15

ATP powered pumps

primary active transport

Answer 15

ATPase driven by ATP hydrolysis

i.e. Na/K pump = 3 Na out + 2 K in against ion gradient

ouabain and digoxin poison

Question 16

ABC Superfamily

Primary active transport

Answer 16

ATP binding cassette
all have common ATP binding domain

i.e. CFTR and MDR (multidrug resistance, normally good for remove toxins but if tumor and overexpress then resist cancer therapy)

Question 17

secondary active transport

Answer 17

transport vs concentration gradient via downhill movement of another molecule (instead of metabolic ATP)
-energy lost by downhill movement captured for other gradient

usually Na+ ion gradient

Question 18

glucose reabsorption @ kidney

secondary active transport

Answer 18

1. secondary active of 2 Na/1 glucose symporter from lumen (low) to epithelial cells (high)
2. facilitated diffusion of glucose out to blood stream (low)

+ primary active transport of Na/K to maintain gradient and keep intracellular low for Na

Question 19

other types of cotransporters/symporters

Answer 19

1. Na/K/Cl
2. K/Cl
3. Na/neurotransmitter (GABA, dopamine)

Question 20

exchanges/antiporters types

Answer 20

1. Na/Ca
2. Na/H

Question 21

types of endocytosis

Answer 21

1. phagocytosis
2. pinocytosis
3. fluid phase
4. receptor mediated
5. caveolae

Question 22

fluid phase endocytosis

Answer 22

uptake of materials into cell dissolved in extracell fluid

low specificity = ineffective

Question 23

receptor mediated endocytosis

Answer 23

highly specific = effective

i.e. clathrin pathway

Question 24

clathrin pathway

Answer 24

1. ligand binds receptor
2. adaptin and clathrin recruited intracell
3. clathrin forms a net that pulls receptors on surface into coated pit
4. coated vesicle forms
5. pinched off by dynamin
6. vesicle uncoats
7. adaptin and clathrin recycled, uncoated vesicle fuses