1. Lecture 3 Membrane Transport
By Dr Nazish

3. 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

4. LECTURE OBJECTIVES Types of membrane transport Simple diffusion.
Osmosis
Osmotic pressue
Osmolarity and tonicity
Composition of body fluids
Facilitated diffusion

5. Membrane transport
active
passive
Simple
diffusion
Vesicular
transport
Active
transport
Facilitated
diffusion
Primary
Active
transport
Secondary
Active
transport
osmosis
Sodium
Potassium pump Co
transport
Counter
transport

6. Membrane Transport Unassisted Transport No need of carrier
(Simple diffusion and osmosis)
Assisted Transport
- Carrier mediated transport
(Facilitated diffusion and active transport)
- Vesicular transport

7. Diffusion Occurs along Concentration gradient
Random movement of molecules.
Down concentration gradient.
To restore steady state .

8. Ions can diffuse down electrical gradient (A difference in charge )

9. Simple diffusion
Occurs through the lipid bilayer or through the protein channels

10. Carrier proteins
Channel
protein
Facilitated
diffusion
Simple
diffusion
Active
transport
diffusion

11. Fick’s law of diffusion
∆C x P x A =
Net rate of diffusion (Q)
MW x ∆X

12. 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)

13. 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.

14. Osmosis: the net diffusion of water down its own concentration gradient.

15. Figure 3.16 Page 76 Membrane (permeable to both water and solute)
H2O moves down
concentration gradient
H2O
Solute
Solute moves down
concentration gradient
Higher H2O concentration,
lower solute concentration
Side 1
Side 2
• Water concentrations equal
• Solute concentrations equal
• No further net diffusion
• Steady state exists
= Water molecule
= Solute molecule

16. Membrane (permeable to H2O but impermeable to solute)
Side 1
Side 2
H2O moves down its
concentration gradient
H2O
Solute unable to move
Higher H2O concentration,
lower solute concentration
Side 1
Side 2
Original
level of
solutions
• Water concentrations equal
• Solute concentrations equal
• No further net diffusion
• Steady state exists
= Water molecule
= Solute molecule

17. • Water concentrations not equal • Solute concentrations not equal
Membrane (permeable to H2O but impermeable to solute)
Hydrostatic
(fluid)
pressure
difference
Original
level of
solutions
H2O
Osmosis
Hydrostatic
pressure
Pure water
Lower H2O conc
higher solute conc
• 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
= Water molecule
= Solute molecule

18. Pressure required to stop osmosis is called as osmotic pressure.

19. osmolarity It is the number of osmoles per liter of the solution.
Osmolarity of human body is 300 mosmoles/litre

20. Interstitial fluid (ISF)
Are identical
Except that
ISF lacks
(PP) plasma
proteins
Presence of PP
only in plasma
creates colloid
osmotic pressure
=25 mmHg
Interstitial fluid (ISF)
Plasma
Cell
Blood
vessel
Extracellular fluid (ECF)
(=ICF & Plasma)
Intracellular fluid (ICF)

21. Extracellular Intracellular fluid fluid
IONIC COMPOSITION OF ECF & ICF ARE COMPLETELY DIFFERENT BUT osmolarity is the same as number of particles /L is the same
Plasma membrane

22. Concentrations of ions in body fluids (mM/liter)
Extracellular fluid
intracellular
Ion
Plasma
interstitial
Na+
145 14
K +
4.2
140
Ca + +
2.5 0!
cl -
110 4
Proteins-
<0.1 45

23. 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.

24. 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.

25. ASSISTED TRANSPORT MECHANISMS

26. 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.

27. Figure 3.19 (1), Page 79 Step 1 Molecule to be transported
Concentration
gradient
ECF
(High)
Conformation X of
carrier (binding sites
exposed to ECF)
Molecule to be
transported binds to
carrier
Plasma
membrane
ICF
(Low)
Carrier molecule
Figure 3.19 (1), Page 79

28. Figure 3.19 (2), Page 79 Step 2 Conformation Y
of carrier
Conformation X of carrier
On binding with
molecules to be
transported, carrier
changes its
conformation
Figure 3.19 (2), Page 79

29. Figure 3.19 (3) Page 79 Step 3 Direction of transport ECF
Conformation Y of
carrier (binding sites
exposed to ICF)
Transported molecule
detaches from carrier
ICF
Figure 3.19 (3) Page 79

30. Figure 3.19 (4) Page 79 Step 4 ECF Conformation X of
carrier (binding sites
exposed to ECF)
After detachment,
carrier reverts to
original shape
ICF
Figure 3.19 (4) Page 79

31. Click to view animation.
Carrier Mediated
Click to view animation.

32. CHARACTERISTICS OF CARRIER MEDIATED TRANSPORT
Specificity
Competition
Saturation

33. Figure 3.20 Page 80 Simple diffusion down concentration gradient
Carrier-mediated
transport down
Concentration
gradient
(facilitated diffusion) Tm
Rate of
transport
of molecule
into cell
Low
High
Concentration of transported
molecules in ECF

34. Thank you
And
Love you all