Session 2.2: Membranes as permeability barriers

Question 1

what is a semi-permeable membrane

Answer 1

a layer through which only allowed substance can pass

Question 2

what is diffusion

Answer 2

movement from a high to low concentration until equilibrium reached (maximum disorder)

Question 3

if there is more the one solute, how will each substance diffuse

Answer 3

independent of other substances, down their own concentration gradients

Question 4

what is passive transport dependent on

Answer 4

permeability and concentration gradient

Question 5

what increases the rate of passive transport

Answer 5

increasing concentration gradient

Question 6

A system is in equilibrium when,

Answer 6

the concentration gradient of a substance is zero so no net flux

Question 7

how does the lipid bilayer form

Answer 7

phospholipids across hole - lipid bilayer forms which is known as black film

Question 8

which molecules are most permeable-least

Answer 8

hydrophobic, small uncharged polar, large uncharged polar, ion (the last 2 cant travel across)

Question 9

examples of hydrophobic molecules

Answer 9

O2, CO2, N2, benzene

Question 10

examples of small uncharged polar molecules

Answer 10

H2O, urea, glycerol

Question 11

examples of large uncharged polar molecules

Answer 11

glucose

sucrose

Question 12

examples of ions

Answer 12

Na+, H+, K+, Ca2+, Mg2+, Cl-, HCO3-

Question 13

the bigger the permeability coefficient

Answer 13

the higher the permeability

Question 14

what makes a permeability coefficent bigger

Answer 14

glucose - glucose transporter
water - lipid
Cl- - ion exchange
when an axon is excited - K+, Na+ (action potential)

Question 15

what are the important roles of transport processes

Answer 15

maintenance of ionic composition
maintenance of intracellular pH
regulation of cell volume
concentration of metabolic fuels and building blocks
extrusion of waste products of metabolism and toxic substances
generation of ion gradients for excitary response

Question 16

how to transport proteins work

Answer 16

facilitated transport through gated pore:

substance enters and binds to transport protein, causes conformational change, so substrate transported

Question 17

how else does facilitated occur via ion channels

Answer 17

the channels open to stimulus, passage of ions down gradient

Question 18

what is an example of faciliated diffusion

Answer 18

ligand-gated ion channels
i) AcH - on neurotransmitter binding, the channel opens, sodium enters the cell
ii) ATP sensitive potassium channel - at rest, K moves outside. when ATP binds, channel closes, prevents movement of K+
voltage gated ion channels:
i) sodium - change in memebrnae potential detected, driving force for voltage sensor, drives conformational change, channel opens, ion flow

Question 19

what are examples of saturated transport processes

Answer 19

facilitated diffusion (majority) - amplify amount of substance that can be transported, enhance permeability
simple diffusion

Question 20

is transport active or passive

Answer 20

i )depends on concentration ratio
passive - towards concentration gradient
active - against concentration gradient
free energy = RTlogC2/C1
ii) depends on membrane potential
pass down electrical gradient - passive
against electrical gradient - active
free energy = RTlogC2/C1 + ZFdeltaPsy

Question 21

as concentration graident or membrnae potential increases

Answer 21

so does gibbs free energy

Question 22

what is active transport

Answer 22

transport of ions or molecules against an unfavourable concentration and/or electrical gradient
requires hydrolysis of ATP
some cells spend up to 30-50% of all ATP they synthesise on active transport

Question 23

if gibbs is positive

Answer 23

transport process is active