TRANSPORT ACROSS CELL MEMBRANE-II

1. بسم الله الرحمن الرحيم TRANSPORT ACROSS CELL MEMBRANE-II • Dr.MohammedSharique 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 • 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 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 • Exocytosis • 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 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, 5th edition • Text book physiology by Guyton &Hall, 12thedition • Text book of physiology by Linda .s contanzo, 3rd edition