L2 Movement of Substances Across Membranes

Question 1

define osmolality

Answer 1

total concentration of all free particles in solution
– mOsmoles/kg (mOsm) of water

*1 mM sol. of Na+ = 1 mOsm
1 mM sol. of NaCl = 2 mOsm

Question 2

define osmolarity

Answer 2

total concentration of all free particles in solution

– mOsmoles/L of water

Question 3

define diffusion

Answer 3

random thermal motion, due to molecular kinetic energy
results in equal distribution of solute throughout a solution

NO concentration gradient!

Question 4

define heat

Answer 4

the amount of energy a particle has - vibrational, kinetic, internal etc.

Question 5

what is simple diffusion?

Answer 5

flux is ALWAYS occurring - there is no net flux!

example C1 vs. C2
the rate at which particles are leaving C1 is = to how fast they are entering C2

Question 6

what is the equation for simple diffusion?

Answer 6

J=P x A ([X0]-[Xi])

the larger the X the larger the J - linear relationship

Question 7

what is permeability related to?

Answer 7

partition, diffusion, thickness

Question 8

what do you need for simple diffusion in lipid bilayer?

Answer 8

pores
channels (selective)
transporters

Question 9

what is a pore?

Answer 9

transmembrane protein that is open

Question 10

what is a channel?

Answer 10

transmembrane protein with a pore that can open and close

Question 11

what is a transporter?

Answer 11

transmembrane protein that undergoes a conformational change and facilitate the transport of a ‘packet’ of substrate across the membrane

Question 12

Characteristics of ligand gated ion channel

Answer 12

the channel is a channel/receptor complex

upon ligand binding - there is a conf. change = opens channel

selectivity - charge and size
selects for cations (+K) and then size - K+ is much larger than Na ion

Question 13

what is an ionotrophic receptor?

Answer 13

ligand gated receptor/channel complex

ligand binds and channel opens

ex. nicotinic receptor

Question 14

what is a metabotrophic receptor?

Answer 14

G protein coupled reaction

activates second messenger system which in turn may activate a remote set of channels

ex. P2Y receptor

Question 15

what are characteristics of voltage gated ion channel?

Answer 15

charged aa inside the channel pore detect the electric field across the membrane

conf. change in response to electric field

Question 16

describe facilitated diffusion?

Answer 16

electrochemical gradient provides driving force

transporters are specific for substrate

unlike channels only a limited amount of molecules can pass at a time

transport shows saturation kinetics - the rate at which the transport open/close will set the max transport rate

more transporters = more flux = walmart example

Question 17

what is primary active transport

Answer 17

require energy ATP in order to move ions AGAINST an EC gradient - this generates voltage across the membrane

ex. Na+-K+-ATPase (3:2 electrogenic)

Question 18

what is secondary active transport?

Answer 18

no hydrolysis of ATP directly

co-transport - both substrates transported in same direction i.e. glucose and Na+

Question 19

what are exchangers?

Answer 19

utilize the EC gradient of 1 substrate to drive another in the opposite direction and up its EC gradient