Membrane Transport and Permeability I

Outline for TodayI. Selective PermeabilityII. TypesIII. Passive Processes

A. Simple diffusionB. OsmosisC. FiltrationD. Facilitated diffusion

IV. Active TransportA. IntroductionB. Solute pumping

1. Na+/K+ ATPase pumpC. Bulk transport

1. Endocytosis2. Exocytosis

Introduction

• Plasma membrane – selectively permeable

• Characteristics that determine permeability– Lipid solubility– Size– Charge/polarity– Presence of channels

& carriers

Selectively Permeable

Fig. 3.6

Introduction• Lipid solubility

– Lipid soluble materials should cross due to non-polar tails of phospholipids

• Size– “size matters”– Restricts larger molecules

• Charge/Polarity– Charged materials won’t

cross– Think of ions

• Channels/Carriers– For ions, aquaporins for

water (at least 10 different types)

– Aquaporin shown on right

http://arbl.cvmbs.colostate.edu/hbooks/molecules/aquaporins.html

General Characteristics

Passive

• Non-energy requiring• Movement must be

favorable– High concentration to low

concentration

• Examples– Simple diffusion– Osmosis– Filtration– Facilitated diffusion (could

be active as well but then usually referred to as solute pumping)

Fig. 3.14

Types of transport

Active

• Active Transport– energy requiring– Movement is non-

favorable• Low concentration to

high concentration

• Examples– Solute pumping– Vesicular transport

Types of transport

Fig. 3.19

Diffusion

HIGH [solute]LOW [solute]

HIGH Osmolarity LOW Osmolarity

[solute] [solute]

Simple Diffusion

• Movement by random motion– Brownian movement

• Favored by the existence of a concentration gradient from one area to another

• [solute] = osmolarity• Diffusion goes from high

osmolarity to low osmolarity– Eventually dynamic

equilibrium is reached

Fig. 3.14

Passive Processes

Simple Diffusion

• Factors affecting diffusion– Temperature

• Higher the temp. the faster it occurs

– Size• Smaller molecules

diffuse faster– SEE GELATIN DEMO

• 294 vs. 738

– Magnitude of the concentration gradient• Greater the gradient the

faster diffusion occurs

Fig. 3.14

Passive Processes

Simple Diffusion

• If a membrane is involved then the following are factors

• Membrane surface area– More surface area =

greater diffusion– Think apical end of some

epithelial cells. WHY?• Membrane permeability

– E.g. potassium ions diffuse easier through a cell membrane than sodium ions

Campbell et al., Fig. 5.11

Passive Processes

Simple Diffusion

• What crosses the cell membrane via simple diffusion?

• H2O, O2, CO2, N2

• Steroids, fat soluble vitamins

• Urea, glycerol, small alcohols, NH3

Campbell et al., Fig. 5.11

Passive Processes

Diffusion

HIGH [solute]LOW [solute]

HIGH Osmolarity LOW Osmolarity

[solute] [solute]

Fick’s Law• Gives variables that affect diffusion• Rate of transfer α A D (C1-C2)

T– Think of general mathematical relationships of

numerator vs. denominator• You will come back to this in the

respiratory system in 1206• (A=area; T=thickness of barrier;

D=diffusion constant; (C1-C2)= concentration difference

Passive Processes

Osmosis

Osmosis

• Diffusion of water through a semi-permeable membrane (solute won’t cross)– Water diffuses down its concentration gradient

Low Osmolarity High Osmolarity high [H2O] low [H2O]

me

mbr

an

e

Direction of water flow

Passive Processes

OsmosisStart: 33% solution

Start: 67% solution

End: 50% solution End: 50% solution

Water

Solute

Passive Processes

Net Diffusion of water

Water loss Water gain

Fig. 3.15

Osmosis

Low Osmolarity High Osmolarity high [H2O] low [H2O]

me

mbr

an

eDirection of water flow

Equilibrium

Passive Processes

Osmosis

• Osmotic Pressure– Pressure of a solution

due to drawing in water• It can be measured• We will study this in

1206 when we study capillary dynamics

Fig. 3.15

Passive Processes

10% solution(hypertonic)

5% solution(hypotonic)

Osmosis• Some new terms• Is a 5% solution a lot?

– Depends upon what is being compared to

• There are terms to describe relative concentrations– Hypertonic

• Has more dissolved material (solute) than another solution

– Hypotonic• Has less dissolved material

(solute) than another solution• In this case the 5% is

hypertonic.– If comparing it to 10%, the 5%

would be hypotonic

Modified fromhttp://proto.thinkquest.nl/~llb082/nl/?thepage=hst1

5% solution(hypertonic)

.9% solution(hypotonic)

Passive Processes

Osmosis

• Isotonic is when both solutions contain the same solute concentration

3 % solution

Modified fromhttp://proto.thinkquest.nl/~llb082/nl/?thepage=hst1

3 % solution

Passive Processes

Osmosis• Hypertonic

– More solute; less water

• Hypotonic– Less solute; more water

• Therefore, water always flows from the hypotonic to the hypertonic

Hypotonic Hypertonic high [H2O] low [H2O]

me

mbr

an

e

Direction of water flow

Passive Processes

Hypotonic Hypertonic high [H2O] low [H2O]

me

mbr

an

eDirection of water flow

Equilibrium

Passive Processes

1% sucrose solution (hypotonic) 10% sucrose solution

(hypertonic)

Campbell et all, Fig. 5.12

IsotonicPassive Processes

Tonicity and Red Blood Cells

Hypotonic Isotonic Hypertonic

High Osm

Low Osm

Net H2OIN

Cells Swell

Osm

Osm

Low Osm

High Osm

Net H2OOUT

Cells Shrink

Crenation

Passive Processes

Fig. 3.16

Starving & Distended Belly

http://www.cs.stedwards.edu/chem/Chemistry/CHEM43/CHEM43/Leukotr/Kwashiorkor.GIF

Kwashiorkor

Passive Processes

OsmosisStart: 33% solution

Start: 67% solution

End: 50% solution End: 50% solution

Water

Solute

Passive Processes

Net Diffusion of water

Water loss Water gain

Filtration

• Movement of substances across a membrane due to hydrostatic pressure (or gravity as shown on the right)– Capillary fluid

movement– kidneys

Passive Processes

Filtration

• Practical applications– Congestive heart

failure

http://www.emedicinehealth.com/articles/10929-9.asp

Passive Processes

Facilitated diffusion

• Transport is facilitated by a membrane protein• Carrier mediated facilitated diffusion

– Protein acts as a carrier– Passive since the movement is still

high low and no ATP is used

Passive Processes

Fig. 3.18

Facilitated diffusion

• Gradient still drives the movement• Notice the change in conformation

Fig. 3.18

Passive Processes

Facilitated diffusion

• Rate of movement is due to the number of carriers– Saturation can occur

so a transport maximum is reached

Passive Processes

Fig. 3.17

Facilitated diffusion

• Types of carriers (can be active or passive)– Uniport

• Carries only one solute at a time

• e.g. Calcium pump (Active)– Symport

• Carries 2 or more solutes through simultaneously

• e.g. sodium and glucose in the intestine and kidney

– Antiport• Carries two or more solutes in

opposite directions• Called countertransport• e.g. sodium-potassium pump

(active)

http://www.vscht.cz/eds/knihy/uid_es-002/motor/index.obrazky.html

Passive Processes