1. TRANSPORT ACROSS CELL MEMBRANE-II
بسم الله الرحمن الرحيم
TRANSPORT ACROSS CELL MEMBRANE-II
Prepared by
Dr.Mohammed Sharique Ahmed Quadri
Assistant prof. Physiology
Al Maarefa College

2. Objectives
Describe how energy from ATP hydrolysis is used to transport ions against their electrochemical concentration differences
Explain how energy from the Na+ and K+ electrochemical gradients across the plasma membrane can be used to drive the net “uphill” (against a gradient) movement of other solutes.
Describe the characteristics of carrier-mediated transport, and distinguish between simple diffusion, facilitated diffusion, and active transport
Describe the process of vesicular transport

3. Active Transport Active transport
Moves a substance against its concentration gradient
Requires a carrier molecule
Requires energy

4. Types of Active Transport
Protein Pumps
Primary active transport
Requires direct use of ATP
Secondary active transport
Driven by an ion concentration gradient established by a primary active transport system
Vesicular transport
Endocytosis
Exocytosis

5. Primary Active Transport
Movement against concentration gradient
Hydrolysis of ATP directly required for the function of the carriers.
Molecule or ion binds to “recognition site” on one side of carrier protein.
Carrier protein undergoes conformational change.
Hinge-like motion releases transported molecules to opposite side of membrane.

6. Primary Active Transport

7. Na+/K+ Pump Carrier protein has enzymes activity ( ATPase)
Extrudes 3 Na+ and transports 2 K+ inward against concentration gradient.

8. Na+/K+ Pump
Steep gradient created by this pump serves following functions:
Provides energy for “coupled transport” of other molecules.
Involvement in electrochemical impulses.
Promotes osmotic flow.

9. Importance of Na+- K+ pump in intestinal epithelium
High osmotic pressure created by movement of sodium causes water to move from intestinal lumen to interstitial space
Protein and glucose r transported actively by cotransport with sodium
Chloride passively follow the electrical gradient created by sodium

10. Secondary Active Transport
Transport of two or more solutes are Coupled .
Energy needed for “uphill” movement obtained from “downhill” transport of Na+.
Hydrolysis of ATP by Na+/K+ pump required indirectly to maintain [Na+] gradient.

11. Secondary Active Transport
Cotransport (symport):
Molecule or ion moving in the same direction as Na+.
Countertransport (antiport):
Molecule or ion moving in the opposite direction of Na+.

13. cotransport

14. Counter transport Molecule or ion moving in the opposite direction
E.g. Na+-Ca2+ exchange
As with cotransport it also uses Na gradient established by the Na+- K+ ATPase as an energy source
Na+ moves downhill & Ca2+ moves uphill

15. Vesicular transport across membrane
Exocytose
Endocytosis

16. Types of Active Transport
Endocytosis: taking bulky material into a cell
Uses energy
Cell membrane in-folds around food particle
“cell eating”
forms food vacuole & digests food
This is how white blood cells eat bacteria!

17. Types of Active Transport
3. Exocytosis: Forces material out of cell in bulk
membrane surrounding the material fuses with cell membrane
Cell changes shape – requires energy
EX: Hormones or wastes released from cell

18. Vesicle-mediated transport Vesicles and vacuoles that fuse with the cell membrane may be utilized to release or transport chemicals out of the cell or to allow them to enter a cell. Exocytosis is the term applied when transport is out of the cell.

20. References Human physiology by Lauralee Sherwood, fifth edition
Text book physiology by Guyton &Hall,11th edition
Text book of physiology by Linda .s contanzo,third edition