ABOUT DIFFERENT MECHANISMS USED TO TRANSPORT ACROSS CELL MEMBRANE

1. DR NILESH KATE
MBBS,MD
ASSOCIATE PROF
DEPT. OF PHYSIOLOGY
TRANSPORT
ACROSS CELL
MEMBRANE.

2. At the end of the class, you must know
1. Importance of cell membrane
2. Types of Transport mechanisms
3. Active transport in detail
4. Primary active transport
5. Secondary active transport
- Co-transport and Counter transport

3. About Cell Membranes
1. All cells have a cell
membrane
2. Functions:
a. Controls what enters
and exits the cell to
maintain an internal
balance called
homeostasis
b. Provides protection
and support for the
cell

4. Structure of Cell membraneStructure of Cell membrane
It is a double layer ofIt is a double layer of
phospholipids – lipidphospholipids – lipid
bilayer.bilayer.
It is an elastic (7.5-10It is an elastic (7.5-10
nm)nm)
It contains almostIt contains almost
proteins calledproteins called
membrane proteinsmembrane proteins

5. 3. Structure of cell membrane
Lipid Bilayer -2 layers of
phospholipids (Gorter &Gorter &
Grendel (1925)Grendel (1925)
a. Phosphate head is polar
(water loving)
b. Fatty acid tails non-polar
(water fearing)
c. Proteins embedded in
membrane
About Cell Membranes (continued)
Phospholipid
Lipid Bilayer

6. Lipid bi-layer

7. Proteins
Polar heads
love water &
dissolve.
Non-polar tails
hide from
water.
Carbohydrate cell
markers
Fluid
Mosaic
Model of
the cell
membrane

8.  4. Cell membranes have pores (holes) in it
a. Selectively permeable: Allows some
molecules in and keeps other molecules out
b. The structure helps it be selective!
About Cell Membranes (continued)
Pores

9. Outside of cell
Inside of cell
(cytoplasm)
Lipid
Bilayer
Proteins
Transport
Protein Phospholipids
Carbohydrate
chains
Structure of the Cell MembraneStructure of the Cell Membrane

10. Membrane Proteins
Integral Proteins: (70% of Cell membrane proteins part
and parcel of membrane structure
Pumps: They transper substances against Concentration
/ Electrical gradients
Channel Proteins: Opened and closed by gates
Carrier Proteins: Involved in transport of substances
Enzyme Proteins: Takes place in membrane reaction
Receptor Proteins: They bear appropriate sites for
recognition of Specific Ligands.

11. Functions of Cell Membrane:
Protective Function
Selective permeability
Absorptive function
Excretory function
Exchange of gases
Maintenance of shape and
 size of the cell.

12. Transport – What it means?  Its highly selective filter,Its highly selective filter,
permits nutrients andpermits nutrients and
leaves the waste productsleaves the waste products
from the cell.from the cell.
 Maintain Homeostasis.Maintain Homeostasis.
 Makes CytosolMakes Cytosol
environment to differentenvironment to different
 Play an important role inPlay an important role in
cell to cell communication.cell to cell communication.
 Its detects ChemicalIts detects Chemical
messengers arriving at themessengers arriving at the
cell surface.cell surface.

13. TRANSPORT MECHANISMSTRANSPORT MECHANISMS
TRANSPORTTRANSPORT
Passive processPassive processActive processActive process
Primary TransportPrimary Transport
Secondary TransportSecondary Transport
Simple diffusionSimple diffusion
Facilitated diffusionFacilitated diffusion
OsmosisOsmosis
Bulk flowBulk flow
FiltrationFiltration

16. FACTORS AFFECTING NET RATE OF
DIFFUSION
FICK’S LAW OF DIFFUSION:
J = - DA X ( C1-C2 ) at particular temperature.
T
D = Diffusion coefficient.
A = Surface area.
C1&C2 = Concentrations on either sides.
(Lipid solubility – It is the major determinant in the
pharmacokinetics of a drug)

17. Factors that Influence Diffusion Rates
 Distance -
 The shorter the distance, the more quickly [ ] gradients are
eliminated
 Few cells are father than 125 microns from a blood vessel
 Molecular Size
 Ions and small molecules diffuse more rapidly
 Temperature -
 ↑ temp., ↑ motion of particles
 Steepness of concentrated gradient -
 The larger the [ ] gradient, the faster diffusion proceeds
 Membrane surface area -
 The larger the area, the faster diffusion proceed

18. Diffusion Across Membranes
 Simple Diffusion
 Lipophilic substances can enter cells easily because
they diffuse through the lipid portion of the
membrane
 Examples are fatty acids, steroids, alcohol, oxygen, carbon
dioxide, and urea,
 Channel-Mediated Diffusion
 Membrane channels are transmembrane proteins
 Only 0.8 nm in diameter
 Used by ions, very small water-soluble compounds
 Much more complex than simple diffusion
 Are there enough channels available?
 Size and charge of the ion affects which channels it can
pass through

19. Diffusion Through the Plasma
Membrane
Figure 3.7

20. OSMOSIS
Osmosis is the process of moving water across a
semi permeable membrane towards ion or solute
rich region in a solution

21. OSMOTIC PRESSURE
The amount of pressure
that can prevent the
movement of water from
another region which is
partitioned by the
permeable membrane
colloidal osmotic
pressure of plasma is 25
mmHg

22. Osmolarity and Tonicity
 Mole - the gram molecular weight of a substance
 1 mole of Glucose =180; 1 mole of NaCl = 58.5
 Molarity - the number of moles of solute per liter of solution
 1.0 M glucose contains 180 g/L; 1.0 M NaCl contains 58.5 g/L
 Most body fluids are less concentrated than 1 M; use mM
(millimolar) or µM (micromolar) concentrations --10-3
and 10-6
,
respectively.
 Osmolarity = the total solute concentration in an aqueous solution
 Osmolarity = molarity (mol/L) x # of particles in solutions
 A 1 M Glucose solution = 1 Osmolar (Osm)
 But a 1 M NaCl soln = 2 Osmolar because NaCl dissociates
into 2 particles (Na and Cl) whereas Glucose does not
 A 1 M MgCl2 solution = what osmolarity???? __________
 Physiological solutions are expressed in milliosmoles per liter
(mOsm/L)
 blood plasma = 300 mOsm/L or 0.3 Osm/L

23. Tonicity
 Tonicity - ability of a solution to affect fluid volume and
pressure within a cell
 depends on concentration and permeability of solute
 Isotonic solution
 solution with the same solute concentration as that of the cytosol;
normal saline
 Hypotonic solution
 lower concentration of nonpermeating solutes than that of the cytosol
(high water concentration)
 cells absorb water, swell and may burst (lyse)
 Hypertonic solution
 has higher concentration of nonpermeating solutes than that of the
cytosol (low water concentration)
 cells lose water + shrivel (crenate)

24. Osmosis and Cells
 Important because large volume changes caused by
water movement disrupt normal cell function
 Cell shrinkage or swelling
 Isotonic: cell neither shrinks nor swells
 Hypertonic: cell shrinks (crenation)
 Hypotonic: cell swells (lysis)

25. Effects of Tonicity on RBCs
Hypotonic, isotonic and hypertonic solutions affect the fluid volume of a red blood
cell. Notice the crenated and swollen cells.

26. VESICULAR TRANSPORT
It is the transport of membrane bounded
substances moving across plasma membrane
It is classified into:
1. Endocytosis 2. Exocytosis.

27. Endocytosis
 It is a process by which the large number of particles
are taken with forming the vesicle into the cell
 It is classified into:
 1. Phagocytosis
 It is a process by which the large number of
particles are engulfed into the cell.
 2. Pinocytosis
 It is a process by which the large number of
particles which are soluble in water are taken into
the cell

28. Endocytosis

29. Receptor Mediated Endocytosis
 A selective process
 Involves formation of vesicles at
surface of membrane
 Vesicles contain receptors on their membrane
 Vesicles contain specific target molecule in high
concentration
 Clathrin-coated vesicle in cytoplasm
 uptake of LDL from bloodstream
 If receptors are lacking, LDL’s accumulate and
hypercholesterolemia develops

30. Receptor Mediated Endocytosis

31. Mechanism of Phagocytosis
The cell membrane invaginates
the material from ECF.
It is pinched off from the
membrane and takes the material
into ICF
The phagocytic cell such as a
macrophage may be attracted to a
particle like a bacteria or virus by
chemical attractant.

32. Pinocytosis
 In the process of pinocytosis the cell membrane forms an
invagination.
 Whatever substance (Proteins) is found within the area of
invagination is brought into the cell.
 In general this material will be dissolved in water and thus
this process is also refered to as "cellular drinking"
 This is opposed to the ingestion
of large particle like bacteria or
other cells or cell debris.

33. Exocytosis
Exocytosis is a process in which an intracellular
vesicle (membrane bounded sphere) moves to
the plasma membrane and fused the
substance into the Extra cellular fluids
For example a few of the processes that use Exocytosis are:
1. Secretion of proteins like enzymes
and antibodies from cells.
2. Release of neurotransmitter from
presynaptic neurons
3. Arosome reaction during fertilization
4. Recycling of plasma membrane

34. ExocytosisExocytosis
The opposite of endocytosis is exocytosis. Large molecules that areThe opposite of endocytosis is exocytosis. Large molecules that are
manufactured in the cell are released through the cell membrane.manufactured in the cell are released through the cell membrane.

35. CMT: Facilitated Diffusion
 Glucose and amino acids are insoluble in lipids and too large
to fit through membrane channels
 Passive process, i.e. no ATP used
 Solute binds to receptor on carrier protein
 Latter changes shape then releases solute on other side of membrane
 Substance moved down its concentration gradient

36. Saturation of a
Carrier Protein
1. When the concentration of x
molecules outside the cell is low, the
transport rate is low because it is
limited by the number of molecules
available to be transported.
2. When more molecules are present
outside the cell, as long as enough
carrier proteins are available, more
molecules can be transported; thus,
the transport rate increases.
3. The transport rate is limited by the
number of carrier proteins and the
rate at which each carrier protein
can transport solutes. When the
number of molecules outside the cell
is so large that the carrier proteins
are all occupied, the system is
saturated and the transport rate
cannot increase.

37. BULK Transport
 The movement of large number of ions,
molecules or particles that are dissolved or
carried in a medium such as a fluid or air is called
bulk flow.
 Rate of Bulk transport is determined by the
differences in hydrostatic pressure or air
pressure.
Eg: 1. Flow of blood within the vessels.
2.Movement of air into and out of the lungs.

38. Active transport Passive transport
Energy is utilisedEnergy is utilised No Energy is utilisedNo Energy is utilised
Movement of ions takes placeMovement of ions takes place
against conc. gradientagainst conc. gradient
Movement of ions takes placeMovement of ions takes place
favouring conc. gradientfavouring conc. gradient
Specific carrier is requiredSpecific carrier is required No carrier is requiredNo carrier is required
Cellular respiratory rate isCellular respiratory rate is No changeNo change
Enzymes are involvedEnzymes are involved No Enzymes are involvedNo Enzymes are involved

40. Types of Cellular Transport
 Passive Transport
cell doesn’t use energy
1. Diffusion
2. Facilitated Diffusion
3. Osmosis
 Active Transport
cell does use energy
1. Protein Pumps
2. Endocytosis
3. Exocytosis
high
low
This is
gonna be
hard
work!!
high
low
Weeee!!!

41. What is active transport?What is active transport?
Active transport is theActive transport is the
transport of substances fromtransport of substances from
a region of lowera region of lower
concentration to higherconcentration to higher
concentration using energy,concentration using energy,
usually in the form ofusually in the form of ATPATP..
Examples: Na, K and CaExamples: Na, K and Ca
active transport.active transport.
1.1.sodium-potassium pumpsodium-potassium pump
2.Calcium pump2.Calcium pump
3.Potassium hydrogen pump3.Potassium hydrogen pump

42. Active Transport
needed for,
1. Maintaining the1. Maintaining the
Chemical and ElectricalChemical and Electrical
Charge at rest.Charge at rest.
2. Intake of Substances
through gated Channels.
3. Collecting of ions with
more concentration.

43. ACTIVE TRANSPORT - WHY ?
 Cells cannot rely solely on
passive movement of
substances across their
membranes.
 In many instances, it is
necessary to move
substances against their
electrical or chemical
gradient to maintain the
appropriate concentrations
inside of the cell or
organelle.

44. Pumps involved in ACTIVE TRANSPORT
1.Sodium-potassium pump
Found in many cells
2.Calcium pump
Found in membrane of
Sarcoplasmic reticulum
3.Potassium hydrogen
pump
Found in Gastrointestine
cell membrane

45. Working of Na-K pumpWorking of Na-K pump

46. Primary active transport
Primary active transport isPrimary active transport is
the transport of sustancesthe transport of sustances
uphill using energy (uphill using energy (ATPATP
hydrolysis)hydrolysis)
It cause a conformationalIt cause a conformational
change that results in thechange that results in the
transport of the moleculetransport of the molecule
through the protein.through the protein.
Eg. Na+-K+ pump.Eg. Na+-K+ pump.

47. Functions of Na+K pumpFunctions of Na+K pump
1.1. It is responsible for
maintaining the high K+
and low Na+
concentration inside the
cell.
2. It maintains intracellular
negativity.
3. Maintains red blood cell
volume.
4. Activate the Carrier
protein.

48. Inhibition of the pump
1. The pump requires binding of Na and K and ATP
for its operation.
therefore ,if the concentration of any of these
substances is low,the pump does function.
2. Decrease in temperature
3. Oxygen lack.
4. Metabolic poisons
Eg.2,4 dinitrophenol prevents the formation of
ATP.

49. Calcium pump Ca+ ATPase pump
 1.Present in the sarcoplasmic
reticulum of muscle cells , which
maintains intracellular ionic
Ca2+ concentration below
0.1mmol/l.
 The direction is from cytoplasm
to ECF.That is why cytoplasm of
most cells have low Ca2+
concentration.

50. Secondary active transport
 The transport of substances against a
concentration gradient involving energy to
establish a gradient across the cell
membrane, utilizes the gradient to transport
a molecule of interest up its concentration
gradient .
 THE TRANSPORT MAY BE
 In the same direction (SYMPORT)
 In the opposite direction (ANTIPORT)

51. Mechanisms of Secondary Active Transport

52. Carriers type processes
 Carriers are transport proteins that binds ions
and other molecules and then change their
configuration moving the bound molecules
from one side of cell membrane to the other.
 Types of carriers :
1.Uniporters
2.Symporters
3.Antiporters

53. UNIPORT
 The movement of
a single
Substance.
 It requires no
energy from the
cell.
 Examples.
 Simple diffusion.
 Facilitated
diffusion.

54. Mechanism of Uniport
Lower concentration regionLower concentration region

55. Symport (Co-transport)
 Transport of two
substances using the
energy produced by
concentration
difference developed by
primary active
transport
 Substances are moving
in the same direction.
 Example: transport of
amino acids, Glucose,

56. Mechanism of Co-transport
ECFECF
ICFICF
ECFECF
ICFICF
ECFECF
ICFICF
sodiumsodium
glucoseglucose

57. Antiport (Counter-transport)
 In this process, the two
substances move across the
membrane in opposite
directions.
 Example:
Exchange of H+ and Na+ in Renal
tubule.

58. MECHANISM OF COUNTER-TRANSPORT
Higher conc. of H+Higher conc. of H+
Lower conc. of H+Lower conc. of H+

59. The Na+, glucose Secondary
Transport
 Sodium co-
transport of
glucose occurs
during absorption
of glucose from the
intestine and
reabsorption of
glucose from renal
tubule.

60. Transport of substances in GIT

61. Transport of substances in Nephron
GG
H+H+
CaCa
CaCa
ClCl

62. Passive Membrane Transport
– Review -
Process Energy Source Example
Simple diffusion Kinetic energy
Movement of O2 through
membrane
Facilitated diffusion Kinetic energy Movement of glucose into cells
Osmosis Kinetic energy Movement of H2O in & out of cells
Filtration Hydrostatic pressure Formation of kidney filtrate

63. Active Membrane Transport –
Review
Process Energy Source Example
Active transport of solutes ATP
Movement of ions across
membranes
Exocytosis ATP Neurotransmitter secretion
Endocytosis ATP White blood cell phagocytosis
Fluid-phase endocytosis ATP Absorption by intestinal cells
Receptor-mediated
endocytosis
ATP
Hormone and cholesterol
uptake
Endocytosis via caveoli ATP Cholesterol regulation
Endocytosis via coatomer
vesicles
ATP
Intracellular trafficking of
molecules

64. OTHER TRANSPORT
PROCESSES
 Across epithelia.
 Through cell proper
 Through tight
junctions
Saturday, October 17, 2015

65. OTHER TRANSPORT
PROCESSES
 Ultra filtration.
STARLING’S FORCES- at
the capillary level
 Plasma osmotic
pressure 25 mm Hg.
 Hydrostatic pressure
Saturday, October 17, 2015

66. Objectives:Objectives:
1. Importance of cell membrane1. Importance of cell membrane
2. Types of Transport mechanisms2. Types of Transport mechanisms
3. Active transport in detail3. Active transport in detail
4. Primary active transport4. Primary active transport
5. Secondary active transport5. Secondary active transport
- Co-transport and Counter transport- Co-transport and Counter transport

67. Thank
You