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

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

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

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

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.

Primary Active Transport

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

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.

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

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.

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+.

cotransport

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

Vesicular transport across membrane Exocytose Endocytosis

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!

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

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.

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