for medical student s

1. Transport of Substances through Cell
Membranes
DR MUHAMMAD MUQEEM MANGI
MBBS. MPhil PHYSIOLOGY
ASSOCIATE PROFESSOR
SULEMAN ROSHAN MEDICAL COLLEGE
TANDO ADAM @ HYDERABAD,SINDH PAKISTAN

2. @theendofslidesstudenthavebasicconceptof:
1. Importanceofcell membrane
2. TypesofTransport mechanisms
3. Activetransportin detail
4. Primaryactive transport
5. Secondaryactive transport
Co-transportandCounter transport
Transport of Substances through Cell
Membranes

3. • The cell perform many functions:
• support, transport, communication, recognition
and acts as selective barriers.
• All these functions are achieved through
movement across cell membranes.
• There are several mechanisms of transport
across cellular membranes. Pathways include
passive and active transport.
Transport of Substances through Cell
Membranes

4. • The Functions of Cell Membrane:
• Protective Function
• Selective permeability
• Absorptive function
• Excretory function
• Exchange of gases
• Maintenance of shape and size of the cell
Transport of Substances through Cell
Membranes

5. Differences between composition of intracellular
and extracellular fluids are caused by transport
mechanisms of cell membrane.
Transport of Substances through Cell Membranes

6. Passive transport
(diffusion)
Active transport Transport of large
particles by
a) Endocytosis
b) Exoocytosis
Transport mechanisms
Simple
diffusion
Facilitated
diffusion
Primary Secondary
Sodium co-transport
mechanism
Sodium counter
Transport mechanism
Transport across cell membrane

7. Transport across cell membrane
• Includes passive and active transport.
• Passive transport includes simple and
facilitated diffusion.
• Active transport includes primary and
secondary active transport.
• Vesicular transport includes Endocytosis and
Exocytosis.

8. Membrane transport proteins
2 major classes of transport proteins:
Carrier Proteins Channel Proteins
lipid
bilayer
solute
olute binding site
ion
aqueous pore
Transport across cell membrane

9. Transport across cell membrane

10. • Diffusion
• Means random
movement of molecules
either thru intermolecular
spaces in the cell
membrane or in
combination with a
carrier protein.
• Energy that causes
diffusion is energy of
normal kinetic motion of
matter. High to Low
Concentration
Transport across cell membrane

11. Transport across cell membrane

12. • Simple diffusion
• Molecules move thru a
membrane without
binding with carrier
proteins.
• Does not require energy
b/c molecules move
across the plasma
membrane down a
concentration gradient or
electrochemical gradient.
Transport across cell membrane

13. • Simple diffusion
• Can occur thru cell membrane by two pathways:
thru the interstices of lipid bilayer and thru watery
channels in some of the transport proteins.
• Transports small non polar molecules (e.g O2 and
N2) and small uncharged, polar molecules
(e.g.H2O,CO2,glycerol).
Transport across cell membrane

14. • Simple diffusion thru
protein channels
• Protein channels are
selectively permeable
to certain substances.
• The channels can be
opened or closed by
gates.
Transport across cell membrane

15. • Gating of protein channels
• Provides a means for controlling the
permeability of the channels.
• Gates are actual gate like extensions of the
transport protein molecule.
Transport across cell membrane

16. Opening and closing of gates
Are controlled in two principal ways:
1. Voltage gating: in this, the molecular
conformation of the gate responds to the
electrical potential across the cell membrane.
2. Ligand gating: some protein channel gates are
opened by binding of another molecule with
the protein; this causes a conformational
change in the protein molecule that opens or
closes the gate.
Transport across cell membrane

17. Transport across cell membrane

18. • Facilitated diffusion
• Is diffusion of a substance
mediated by a carrier.
• FD occurs thru ion
channels or carrier
proteins.
• Is down the
electrochemical gradient.
Transport across cell membrane

19. • Facilitated diffusion
• Does not require
energy.
• Differs from simple
diffusion in that the
rate of diffusion
approaches a
maximum, called Vmax
as the conc. of
substance increases.
Transport across cell membrane

20. Transport across cell membrane

21. • Characteristics of Facilitated diffusion
• Specificity
• Vmax
Transport across cell membrane

22. Transport across cell membrane

23. • Examples of substances transported by
facilitated diffusion
• Glucose
• Amino acids.
• Mannose
• Galactose
• Xylose
• Arbinose
Examples of substances transported by
facilitated diffusion
Transport across cell membrane

24. • Osmosis
• Is the flow of water across a semi permeable
membrane from a solution with low solute
concentration to a solution with high solute
concentration.
• Osmotic pressure is determined by number of
particles per volume of fluid.
Transport across cell membrane

25. • Osmosis is the diffusion of water through a selectively
permeable membrane like the cell membrane
Water diffuses across a membrane from an area of high
concentration to an area of low concentration.
Semi-permeable membrane is permeable to water, but not to sugar
Transport across cell membrane

26. Transport across cell membrane

27. • Osmole, osmolality and osmolarity:
• To express the concentration of solution in
terms of number of particles unit osmole is
used.
• Osmolar concentration expressed as osmoles
per kilogram of solution is osmolality.
• Osmolar concentration expressed as osmoles
per liter of solution is osmolarity.
Transport across cell membrane

28. Transport across cell membrane

29. • Active transport:
• Occurs in combination of a carrier protein.
• Occurs against the concentration gradient.
• Requires energy.
• Is of two types,
– primary active transport
– secondary active transport.
Transport across cell membrane

30. • Primary Active
transport:
• In primary active
transport, energy is
derived from
breakdown of ATP.
• Example is sodium
potassium pump.
Transport across cell membrane

31. Transport across cell membrane

32. Transport across cell membrane

33. • Examples of primary active transport
• Sodium ions
• Potassium ions
• Hydrogen ions
• Calcium ions
• Chloride ions
Transport across cell membrane

34. • Importance of Na-K pump
• It controls the cell volume by controlling the
concentration of solutes inside the cell and
thus minimizing osmotic effects.
• It establishes Na+&K+ concentration gradients
across the plasma membrane of all cells, these
gradients are critically important in the ability
of nerve and muscle cells to generate
electrical signals.
Transport across cell membrane

35. • Importance of sodium potassium
pump
• The energy used to run the Na+ K+ pump also
indirectly serves as the energy source
• for secondary active transport.
Transport across cell membrane

36. • Secondary active
transport
• In secondary active
transport energy is
derived by ionic
concentration gradient
created by primary
active transport.
Transport across cell membrane

37. • Secondary active transport
• Has two types:
1. Sodium Co-transport mechanism
2. Sodium Counter transport mechanism
Transport across cell membrane

38. • Sodium Co-
transport
• In this mechanism, a
substance is
transported along with
sodium in the same
direction, and is
therefore called,
sodium co transport
mechanism.
Transport across cell membrane

39. Symport
Transport across cell membrane

40. • Examples of Co-transport
• sodium glucose co-transport.
• sodium amino acids co-transport
• sodium potassium-two chloride co-transport
Transport across cell membrane

41. • Sodium counter transport:
• In this mechanism, sodium and the other
substance move in opposite direction.
• Example: sodium-calcium counter transport
Sodium-hydrogen counter transport
Transport across cell membrane

42. Two Substrate Bind to the opposite sides of the
transport.
One substrate( Na+) is travelling downhill & will
energize transport of another substrate ( Ca+)
Transporter changes orientation with respect to
inner and outer membrane surface
After being transported across the membrane,
both substrate are released and the protein is
ready for an other cycle
Antiport
Transport across cell membrane

43. Transport across cell membrane

44. • Endocytosis
• Is the entry of large particles into the cell.
• Occurs in two forms:
• Pinocytosis (cell drinking)
• Receptor mediated endocytosis
• Phagocytosis (cell eating)
Transport across cell membrane

45. • Pinocytosis
• Occurs in all cells of the body.
• is the only means by which very large
macromolecules such as protein molecules
can enter the cell.
Transport across cell membrane

46. • Pinocytosis
• Occurs in all cells of the
body.
• is the only means by
which very large
macromolecules such as
protein molecules can
enter the cell.
Transport across cell membrane

47. Receptor mediated Endocytosis
Transport across cell membrane

48. Transport across cell membrane

49. • Phagocytosis
Involves large particles
rather than molecules.
• Occurs only in certain
cells such as
macrophages and some
of the white blood cells.
Transport across cell membrane

50. • Phagocytosis
• In phagocytosis of bacteria, bacteria attach to
antibodies and then to the receptor. This
intermediation of antibodies is called opsonization.
• Phagocytic vesicle is larger than the pinocytic vesicle.
Transport across cell membrane

51. • Exocytosis
• Is release of substances
originating within the
cell to the exterior.
• Is the primary
mechanism for
accomplishing
secretion.
Transport across cell membrane

52. • Exocytosis
• the cell to add specific components to the
membrane, such as selected carriers, channels
or receptors.
Transport across cell membrane