membranetransport-220930062006-3063be2c.pptx

membrane transport

1. Mr. Vijay Salvekar Associate Professor GRY Institute of Pharmacy,Borawan

2. Principles of membrane transport (1 ) Membranes are barriers to movement of water-soluble molecules.

3. Principles of membrane transport Two classes of transport -channels -carriers (=transporters, carriers, exchangers) Type of transport distinguished based upon how energy is used

4. Passive and facilitated diffusion movements of molecules from one site from high concentration to low concentration is diffusion Passive diffusion is unassisted Its facilitated diffusion if a protein allows diffusion across a membrane barrier Channels ( with selective permeability ) allow diffusion of ions down their

5. Active transport Cells can use various forms of energy to drive transport against concentration or charge gradients What kind of energy is used? transport of some molecules fueled by the energy of ATP membrane potential can drive the transport of charged molecules Light Transport that uses energy directly is considered primary active transport

6. Concentration Gradient The formal definition of a  concentration gradient  is the process of particles, which are sometimes called solutes, moving through a solution or gas from an area with a higher number of particles to an area with a lower number of particles. The areas are typically separated by a membrane. electrochemical gradient. it is a  gradient  of  electrochemical  potential, usually for an ion that can move across a membrane. The  gradient  consists of two parts , the chemical   gradient , or difference in solute concentration across a membrane, and the  electrical gradient , or difference in charge across a membrane.

7. Terms and distinctions Uniporter : movement of one molecule Coupled carriers : movement of one molecule in conjunction with a second - Symport : both molecules in the same direction - Antiport : molecules move in opposite directions (exchangers) Electrogenic : movement results in the transfer of a charge Electroneutral : no change in net charge as a result of transport

8. ATPases Many proteins use the energy of ATP hydrolysis to fuel transport. (1) P-type ATPase Ca 2+ - ATPase is important in muscle activation is important in acid secretion in stomach

9. ATPases ( 2) V-type ATPase Multimeric transporters often work in the reverse direction (ATP synthesis) F 1 Fo ATPase is the mitochondrial ATP synthase H + - ATPase of lysosomes acidify the organelle

10. ATPases (3) ABC Transporters Many proteins have an “ATP-Binding Cassette” and move large molecules across membranes

11. Ion channels Ion channels are pores that permit the movement of specific ions. When open, the channels allow ions to move down concentration gradients

12. Ion channels Can “transport” 100,000,000 ions/ sec A “selectivity filter” restricts movement to specific ions

13. Ion channels Movement is controlled by regulating “openness” –the proportion of time spent in the open configuration Ion channels can be regulated by specific conditions to be open or closed If opened for a prolonged period, the channels can become desensitized

14. Ion channels

15. Types of ion channels (1) Ligand -gated channels: Usually opened by intracellular or extracellular ligands e.g. IP 3 -sensitive Ca 2+ channel opens in the presence of IP 3

16. Ion channels (2) Voltage-gated channels: Altering voltage beyond a threshold will cause the channel to open.

17. Ion channels (3) Mechanically-gated channels: e.g. “stretch-activated channels” open when cell shape is altered. Since channel is attached to the cytoskeleton, stretching causes a physical change in the protein