transport across cell membrane

1. TRANSPORT
ACROSS CELL
MEMBRANE.

2. At the end of the lesson, 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 membrane
It is a double layer of
phospholipids – lipid
bilayer.
It is an elastic
It contains almost
proteins called
membrane proteins

5. 3. Structure of cell membrane
Lipid Bilayer -2 layers of
phospholipids (Gorter &
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)
d
yer
Proteins
Transport
Protein Phospholipids
Carbohydrate
chains
Structure of the Cell Membrane

10. Membrane Proteins
Integral Proteins: (70% of Cell membrane proteins part
and parcel of membrane structure
Pumps: They transfer 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 does it
means?
 Its highly selective filter,
permits nutrients and
leaves the waste products
from the cell.
 Maintain Homeostasis.
 Makes Cytosol
environment to different
 Play an important role in
cell to cell communication.
 Its detects Chemical
messengers arriving at the
cell surface.

13. TRANSPORT MECHANISMS
TRANSPORT
Passive processActive process
Primary Transport
Secondary Transport
Simple diffusion
Facilitated diffusion
Osmosis
Bulk flow
Filtration

15. Tuesday, September 3, 2019
Diffusion is net movement of anything (e.g., atom, ions,
molecules) from a region of higher concentration to a region of
lower concentration. Diffusion is driven by a gradient in
concentration.

16. FACTORS AFFECTING NET RATE OF
DIFFUSION
FICK’S LAW OF DIFFUSION:
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. Tuesday, September 3, 2019

22. 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)

23. 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)

24. 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.

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

26. 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 (“cell eating”)
 It is a process by which the large number of
particles are engulfed into the cell.
 2. Pinocytosis (“ cell drinking”)
 It is a process by which the large number of
particles which are soluble in water are taken
into the cell

27. Endocytosis

28. 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

29. Receptor Mediated Endocytosis

30. 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.

31. 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.

32. 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

33. Exocytosis
The opposite of endocytosis is exocytosis. Large molecules that are
manufactured in the cell are released through the cell membrane.

34. 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

35. 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.

36. Active transport Passive transport
Energy is utilised No Energy is utilised
Movement of ions takes place
against conc. gradient
Movement of ions takes place
favouring conc. gradient
Specific carrier is required No carrier is required
Cellular respiratory rate is No change
Enzymes are involved No Enzymes are involved

38. 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!!!

39. What is active transport?
Active transport is the
transport of substances from
a region of lower
concentration to higher
concentration using energy,
usually in the form of ATP.
Examples: Na, K and Ca active
transport.
1.sodium-potassium pump
2.Calcium pump
3.Potassium hydrogen pump

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

41. 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.

42. 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

43. Primary active transport
Primary active transport is
the transport of substances
uphill using energy (ATP
hydrolysis)
It cause a conformational
change that results in the
transport of the molecule
through the protein.
Eg. Na+-K+ pump.

44. 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)

45. Mechanisms of Secondary Active Transport

46. 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

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

48. Mechanism of Uniport
Lower concentration region

49. 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,

50. Mechanism of Co-transport
ECF
ICF
ECF
ICF
ECF
ICF
sodium
glucose

51. 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.

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

53. 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.

54. 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

55. 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