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Lecture 3 Membrane Transport
By Dr Nazish
A 24 years old boy was severely injured in a road traffic accident and
had excessive blood loss. He was brought to the emergency
department. On examination he had a very weak pulse and his blood
pressure was 80/50mmHg.His blood group was B+ve
LECTURE OBJECTIVES
Types of membrane transportSimple diffusion.
OsmosisOsmotic pressue
Osmolarity and tonicityComposition of body fluids
Facilitated diffusion
Membrane transport
Simple diffusion Active
transport
Facilitateddiffusion
osmosis
PrimaryActive
transport
SecondaryActive
transport
SodiumPotassium pump
Co transport
Countertransport
Vesicular transport
passive active
Membrane Transport
Unassisted TransportNo need of carrier
(Simple diffusion and osmosis)Assisted Transport
- Carrier mediated transport(Facilitated diffusion and active transport)
- Vesicular transport
Diffusion Occurs along Concentration gradientConcentration gradient
• Random movement of molecules.• Down concentration gradient. • To restore steady state .
Ions can diffuse down electrical gradient Ions can diffuse down electrical gradient ((A difference in charge )
Simple diffusion
• Occurs through the lipid bilayer or through the protein channels
Channel protein
Carrier proteins
Simple diffusion
Facilitated diffusion
Activetransportdiffusion
Fick’s law of diffusion
Net rate of diffusion (Q)∆C x P x A
MW x ∆X=
By Fick’s law of diffusion: Factors affecting the rate of diffusion.• the magnitude of the concentration gradient (∆C) • the permeability of the plasma membrane to a
substance. ( P)• the surface area of the membrane across which
diffusion takes place. (A)• the molecular weight of a substance. (MW)• the distance through which diffusion takes place
(∆X)
Simple Diffusion
It is the movement of the molecules down the concentration, electrical or pressure gradient with the use of the kinetic motion of the molecules.
Osmosis: the net diffusion of water down its own concentration gradient.
Membrane (permeable to both water and solute)
Higher H2O concentration,lower solute concentration
H2O moves down concentration gradient
Solute moves down concentration gradient
• Water concentrations equal• Solute concentrations equal• No further net diffusion• Steady state exists
Side 1 Side 2
= Water molecule
= Solute molecule
Figure 3.16 Page 76
H2O
Solute
= Water molecule
= Solute molecule
Membrane (permeable to H2O but impermeable to solute)
Higher H2O concentration,lower solute concentration
H2O moves down its concentration gradient
• Water concentrations equal• Solute concentrations equal• No further net diffusion• Steady state exists
Solute unable to move
Side 1 Side 2
Side 1 Side 2
Originallevel ofsolutions
H2O
= Water molecule
= Solute molecule
Membrane (permeable to H2O but impermeable to solute)
Pure water Lower H2O conchigher solute conc
Originallevel ofsolutionsH2O
• Water concentrations not equal• Solute concentrations not equal• Tendency for water to diffuse by osmosis into side 2 is exactly balanced by opposing tendency for hydrostatic pressure difference to push water into side 1• Osmosis ceases• Opposing pressure necessary to completely stop osmosis is equal to osmotic pressure of solution
Hydrostatic(fluid)pressuredifference
Osmosis
Hydrostatic pressure
Osmotic pressure
Pressure required to stop osmosis is called as osmotic pressure.
osmolarity
• It is the number of osmoles per liter of the solution.
• Osmolarity of human body is 300 mosmoles/litre
Cell
Interstitial fluid (ISF)
Blood vessel
Plasma
Extracellular fluid (ECF) (=ICF & Plasma)
Intracellular fluid (ICF)
Are identicalExcept thatISF lacks(PP) plasma proteinsPresence of PPonly in plasma creates colloidosmotic pressure=25 mmHg
IONIC COMPOSITION OF ECF & ICF ARE
COMPLETELY DIFFERENT
BUTosmolarity is the same as number
of particles /L is the same
Pla
sma
mem
bra
ne
Extracellular fluid
Intracellular fluid
Concentrations of ions in body Concentrations of ions in body fluids (mM/liter)fluids (mM/liter)
Extracellular fluidExtracellular fluid intracellulaintracellularr
IonIon Plasma Plasma interstitiainterstitiall
NaNa++ 145145 1414
K K ++ 4.24.2 140140
Ca Ca + ++ + 2.52.5 0!0!
cl cl -- 110110 44
ProteinsProteins-- 1414 <0.1<0.1 4545
Tonicity of a solution is the effect the solution has on cell volume.
• An isotonic solution has the same concentration of nonpenetrating solutes as normal body cells.
• A hypotonic solution has a lower concentration of nonpenetrating solutes compared to normal
body cells.• A hypertonic solution has a higher concentration
of no penetrating solutes compared to normal body cells.
A 24 years old boy was severely injured in a road traffic accident and had excessive blood loss.
He was brought to the emergency department. On examination he had a very weak pulse and his blood
pressure was 80/50mmHg.His blood group was 0-ve.
Doctors were not able to find out his matching blood group in emergency.
What type of fluid imbalance do you expect in this patient.What will happen to the volume and shape of his body
cells.What would be the effects on osmolarity of the ECF and ICF
of the patient.What type of the fluid would be given to the paient to save
his life.
ASSISTED TRANSPORT MECHANISMS
Facilitated diffusion is a type of assisted transport.
• By this process a substance moves from a higher to a lower concentration.
• Unlike simple diffusion, facilitated diffusion requires a carrier molecule.
• Glucose is transported into cells by facilitated transport.
Step 1
Conformation X ofcarrier (binding sitesexposed to ECF)Molecule to betransported binds tocarrier
Molecule to betransported
Concentrationgradient
Plasmamembrane
Carrier molecule
(Low)
(High)ECF
ICF
Figure 3.19 (1), Page 79
Step 2
On binding withmolecules to betransported, carrierchanges itsconformation
Conformation X of carrier Conformation Yof carrier
Figure 3.19 (2), Page 79
Step 3
Conformation Y ofcarrier (binding sitesexposed to ICF)Transported moleculedetaches from carrier
Direction oftransport
ECF
ICF
Figure 3.19 (3)Page 79
Step 4
ECF
ICF
Conformation X ofcarrier (binding sitesexposed to ECF)After detachment,carrier reverts tooriginal shape
Figure 3.19 (4)Page 79
Click to view animation.
Carrier Mediated
Animation
CHARACTERISTICS OF CARRIER MEDIATED TRANSPORT
• Specificity
• Competition
• Saturation
Simple diffusion down concentration gradient
Rate oftransportof moleculeinto cell
Concentration of transportedmolecules in ECF
Carrier-mediated transport down Concentrationgradient(facilitated diffusion)
Low High
Tm
Figure 3.20Page 80
Thank youAnd
Love you all
Thank youAnd
Love you all
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