presentation over transport mechanism of plasma membrane

1. TRANSPORT
ACROSS CELL
MEMBRANE.
Presented By:
Abhay Pandit

2. Introduction
2
• All communication between cell and extracellular
medium is mediated through cell membrane.
• In this sense PM has dual functions:
• A. It must retain dissolved material inside the cell
• B. It must allow necessary exchange of material in and
out of the cell.
• Through cell membrane substances may diffuse
• Cell permeability determine which substances can
enter the cell, many of which may be necessary to
maintain its vital processes and the synthesis of living
substances.

3. It is a double layer of phospholipids –
lipid bilayer.
It is an elastic (7.5-10 nm)
It contains almost proteins called
membrane proteins

5. 1.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
Phospholipid
Lipid Bilayer

6. • 1. 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!
Pores

7. • Ions, hydrophilic molecules larger than water, and large
molecules such as proteins do not move through the membrane on
their own.
• Membrane is impermeable to large & polar-molecules (ions,
proteins & polysaccharides)
• Membrane is permeable to Nonpolar & hydrophobic molecules like
lipid and small molecules (O2, CO2, N2, NO etc)
• Thus, permeability depends on solubility, charge or solute size.
Semipermeable nature of Membrane

8. Protective Function
Selective permeability
Absorptive function
Excretory function
Exchange of gases
Maintenance of shape and
Size of the cell.

9. Transport – What it means?
 Its highly selective filter, permits nutrients
and
leaves the waste products from the cell.
 Maintain Homeostasis.
 Play an important role in cell to cell
communication.
 Its detects Chemical messengers arriving at
the cell surface.

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

12.  Cell doesn't uses energy-
Diffusion
Osmosis
Bulk Transport
high
low
Weeee!!!

13. 13
DIFFUSION
Diffusion is a
PASSIVE process
which means no
energy is used to
make the
molecules move,
they have a
natural KINETIC
ENERGY

14. • Distance -
– The shorter the distance, the more quickly concentration
gradients are eliminated
• Molecular Size
– Ions and small molecules diffuse more rapidly
• Temperature -
–  temp.,  motion of particles
• Steepness of concentrated gradient -
– The larger the concentration gradient, the faster diffusion
proceeds
• Membrane surface area -
– The larger the area, the faster diffusion proceed

15. 15
Simple Diffusion
• Requires NO
energy
• Molecules
move from
area of HIGH
to LOW
concentration

16. Permeable membrane: Membrane, which allows passage
of both solute and solvent molecules indiscriminately.
Semipermeable membrane: allows passage of solvent
molecules but not solute molecules.
Differentially permeable membrane: Allows passage of
some solute molecules along with solvent molecules.
Osmotic pressure (OP):is a pressure equivalent to
prevent the passage of solvent (like water) molecule
from a low concentration to high concentration zone
through SPM, thereby preventing increase in the volume
of that solution.

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

19. • 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)

20. • 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
– Hypotonic: cell swells

21. Hypotonic, isotonic and hypertonic solutions affect the fluid volume of a
red blood cell.

22.  Cell does use energy :-
 Protein Pumps
 Endocytosis
 Exocytosis
high
low
This is gonna
be hard
work!!

23. 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.

24. 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.

25. 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.

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

27.  It is a process by which the large number
of particles are taken with forming the
vesicle into the cell.
 The cell membrane invaginates the
material from ECF.
It is pinched off from the membrane and
takes the material into ICF

28. 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. Acrosome reaction during fertilization

29. 29
Facilitated Diffusion
Permeases may be passive (facilitated diffusion) or an active
transport one
Along concentration gradient.
When the permeases operate against gradient called active
transport
copyright cmassengale

30. 30
Facilitated Diffusion Mechanism
1.Some Carrier
proteins do not
extend through the
membrane.
• They bond and
drag molecules
through the lipid
bilayer and
release them on
the opposite side.
2 hypothesis: 1. Carrier mechanism and 2. Fixed pore mechanism

31. 2. Fixed pore mechanism:
In this mechanism the carrier is represented by integral proteins that
transverse the membrane and which, once bound to the molecule to be
transported, undergo conformational changes. Example is penetration of
anions into RBC.
• Other carrier
proteins
change shape
to move
materials
across the cell
membrane

32. 32
• Fixed pore mechanism seems more
acceptable because it requires less
energy.
• Conformational change in fixed pore
mechanism is thermodynamically
feasible.
• Carrier mechanism is less acceptable
because:
• It requires more energy.
• Rotation is thermodynamically difficult.

33. Primary active transport
Primary active transport is
the transport of sustances
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.

34. 1. It is responsible
for maintaining the
high K+ and low
Na+ concentration
inside the cell.
2. It maintains
intracellular
negativity.

35.  It moves multiple molecules across the
membrane, powering the uphill
movement of one of molecules with
downhill movement of other molecules.
 THE TRANSPORT MAY BE
 In the same direction (SYMPORT)
Ex. SGLT2 glucose transporter.
 In the opposite direction (ANTIPORT)
Ex. Na+/Ca2+ in cardiomyocyte. (heart
cell)

37. • Cell biology- Karp, sixth edition
• Life sciences- Pathfinder
• ^Campbell, Neil A.: Brad Williamson; Robin J.
Heyden (2006). Biology exploring life.ps:
• https://www.khanacademy.org