Transport mechanisms Passive transport

1. Transport mechanisms:
By
Dr. Harinatha Reddy A
Assistant Professor
Department of Biotechnology
CHRIST UNIVERSITY

3.  The plasma membrane forms a barrier that blocks the free
exchange of molecules between the cytoplasm and the external
environment of the cell.
 Specific transport proteins (carrier proteins and channel
proteins) then mediate the selective passage of small molecules
across the membrane.

4. Transport mechanisms:
 Passive transport
 Active transport

6. Passive transport:
 The simplest mechanism by which molecules can cross the
plasma membrane is passive diffusion.
 During passive diffusion, a molecule simply dissolves in the
phospholipid bilayer, diffuses across it.

7.  Passive diffusion do not require ATP energy.
 The net flow of molecules is high concentration to lower
concentration of the molecule.

8.  Importantly, only small, relatively hydrophobic molecules are able
to diffuse across a phospholipid bilayer at significant rates.
 Thus gases 02 and C02 , benzene, H20 and ethanol are able to
passively diffuse across the plasma membrane.

9.  The small ions such as H+, Na+, K+ and Cl- and uncharged polar
molecules such as glucose are unable to cross the plasma membrane
by passive diffusion.
 The passage of these molecules across the membrane instead
requires the activity of Carrier and channel proteins.

10. They are three main kinds of passive transport are:
 Simple diffusion,
 Facilitated diffusion,
 Osmosis.

11. Simple diffusion:

12. Simple diffusion:
 Simple Diffusion is the net movement of solute from high
concentration to lower concentration.
 The difference of solute concentration between the two areas is
often termed as the concentration gradient.
 Diffusion will continue until this gradient has been eliminated.

13.  Simple diffusion and osmosis are in some ways similar.
 Simple diffusion and osmosis are both forms of passive transport
and do not require ATP energy.

14. FACILITATED DIFFUSION :
 Facilitated diffusion differs from passive diffusion in that the
transported molecules do not dissolve in the phospholipid bilayer.
 Their passage is mediated by proteins in the membrane.

15. Two classes of proteins that mediate facilitated diffusion.
1. Carrier proteins
2. Channel proteins (Ion pumps)

16. 1.Carrier proteins:

17.  Carrier proteins bind specific molecules and undergo
conformational changes that allow the molecule to pass through the
membrane and be released on the other side.
 Carrier proteins are responsible for the facilitated diffusion of
sugars, amino acids, and nucleosides across the plasma
membranes of most cells.
1.Carrier proteins:

18. Channel proteins:

19.  Channel proteins form open pores through the membrane,
allowing the free diffusion of any molecule of the appropriate size
and charge.
Channel proteins:

20. OSMOSIS:
 The net movement of water molecules through a partially
permeable membrane from a solution of high water potential to
an area of low water potential.

21.  There are three types of Osmosis solutions: the isotonic solution,
hypotonic solution, and hypertonic solution.

22.  Isotonic solution: is when the extracellular solute concentration is
balanced with the concentration inside the cell.

23.  Hypotonic solution is when the solute concentration outside the
cell is lower than the concentration inside the cell.
 In hypotonic solutions, the water moves into the cell, down its
concentration gradient, That can cause the cell to swell.

24.  Hypertonic solution is when the solute concentration is higher
than the concentration inside the cell.
 In hypertonic solution, the water will move out, causing the
cell to shrink.